Virginia Tech® home

Electrical Safety in Research Operations

Researcher in lab conducting electrical experiment
Photo: Jim Stroup for Virginia Tech.

Electrical Safety in Research Online Program

Applies to:

This program applies to personnel who face a risk of electrical shock or related injuries from work on energized electrical systems at designated thresholds identified in this program. Personnel working on or near energized electrical systems must be "qualified." This program sets forth the policy for working on energized systems and the process by which personnel become "qualified." This program relies heavily on the Department of Energy's Handbook 1092-2013, and the 2021 edition of the National Fire Protection Association's 70E, "Handbook for Electrical Safety in the Workplace."

Note: Electrical research operations must be supervised by a "qualified person," and where personnel may be exposed to shock or arc-flash events, additional training is required. The design and use of electrical research systems must comply with the requirements of this program.


  • New electrical wiring, the modification, extension, or replacement of existing wiring must conform to the requirements of the National Electric Code (NEC), the Virginia Uniform Statewide Building Code, and Occupational Safety and Health (OSHA). Requirements and oversight are provided by the Virginia Tech Office of the University Building Official.
  • All personnel who face a risk of electrical shock, burns, or related injuries must be trained in electrical safe work practices and be "qualified."
  • Awareness level training is available for "unqualified" persons who use extension cords, GFCIs, or where more information regarding basic electrical hazards and controls is desired.
  • Qualified Persons must attend Environmental Health & Safety Electrical Qualified Person (for tradional electrical hazards) and/or Electrical Safety for Research (for non-tradional electrical hazards) training. Additional training includes:
    • Lockout/Tagout Authorized Person.
    • First Aid/CPR/AED.


Environmental Health & Safety developed this program to reduce exposures related to energized electrical work and to assure the safety of personnel who face a risk of electrical shock, arc flash events, or related injuries as part of their electrical research project. The Electrical Safety Program also assures that all departments that perform electrical research activities follow uniform work practices.


Each department that performs research activities covered by this program must designate one or more employee(s) to coordinate the requirements of this program at departmental sites. 

All construction, renovation, and maintenance of university facilities must be in accordance with University Policy 5405 to ensure full compliance with the design and execution of the work with applicable codes, standards, permitting requirements, and other university concerns.


This program provides a system for ensuring that personnel performing energized electrical work, including voltage testing and diagnostics, are trained in the safety aspects of such work and have been qualified by their principal investigator to perform the task assigned. The training offered by Environmental Health & Safety associated with this program covers personal safety issues regarding work on electrical systems and includes relative information to be gathered while analyzing electrical-related hazards, which safe work practices may apply, and selection, use, and care of appropriate electrical-related personal protective equipment.  

Qualified persons are those who have received specific training and have demonstrated the skills necessary to work safely on or near exposed energized parts. A person may be qualified to work, for example, on circuits at 240 volts, but may be unqualified to work on capacitors.

Only qualified persons may place or remove locks and tags on energized electrical systems.

Unqualified persons are those with little or no such training.

The principal investigator or other designated departmental representative should use the following general guidelines to determine whether an individual is qualified for a specific electrical task. Different subsets of these criteria should be selected according to the exact nature of the task. The departmental representative should only authorize the task if he/she is satisfied that all relevant criteria are met. If it cannot be independently verified that an employee is qualified, assistance from the principal investigator or Environmental Health & Safety should be obtained.

  1. Describe in detail the scope of the task.
  2. Can the individual identify all possible electrical exposures?
  3. Does the individual have experience in the selection of test equipment for this job? What test equipment will be used?
  4. Does the individual know how to check the equipment calibration, condition, and operation?
  5. Does the individual know how to shut down, isolate, and verify all sources of energy that may cause harm?
  6. Is the individual aware of lockout/tagout (LO/TO) requirements and trained in LO/TO if required?
  7. Can the individual identify, interpret, and implement all applicable codes and standards pertaining to the task?
  8. Does the individual have the experience and training to independently distinguish correct construction techniques from incorrect techniques?
  9. Does the individual have the experience and training to select the correct materials and components and to use them in a manner consistent with their manufacture and/or listing?
  10. Can the individual distinguish between appropriate and inappropriate equipment grounding techniques? Is the individual thoroughly familiar with specific equipment grounding requirements for this apparatus?
  11. Does the individual have the experience and training to predict all likely failure modes of a particular construction, and to properly mitigate the effects of such failures?

This program applies to work performed by persons working on or near research applications involving electrical systems, equipment, or components used in non-traditional applications such as research and development. Safe work practices also apply to work performed by unqualified persons near energized electrical conductors, equipment, or systems.

It is university policy to de-energize live parts, whenever possible, before working on or near them. Systems or equipment must be de-energized using approved lockout/tagout procedures in accordance with Virginia Tech's Lockout/Tagout Program. This is the preferred method for protecting personnel from electrical hazards. Personnel are permitted to work on, or near, exposed live parts only if an overriding reason necessitates the practice. Justification would include diagnostics, troubleshooting, and testing.

It is not feasible to develop a single set of safety requirements for energized work that covers every electrical task. It is the collective responsibility of the principal investigator or program supervisor and the department to assure that the safeguards for a specific operation effectively protect workers, students, and visitors against electrical hazards.

Personnel must be qualified to perform the electrical tasks assigned. The principlal investigator or program supervisor should refer to guidelines in "Qualifying criteria" section of this program the to make that determination.

In general, electrical work can be organized into seven classifications according to the degree of energy present, and three modes, according to the operational status of the equipment/system.

Mode 0 (electrically-safe work condition):

All operations are conducted in a de-energized state in which locks/tags have been applied to all hazardous energy sources. Refer to requirements for establishing an electrically-safe work condition (i.e. lockout/tagout) for meeting this mode.

Mode 1 (establishing an electrically-safe work condition):

The process to achieve Mode 0 is considered energized electrical work until verification of a zero energy state is accomplished. In other words, the system is assumed and treated as energized until proven to be positively de-energized. The use of personal protective equipment may be required during this process if power source thresholds are met and approach boundaries are crossed. Refer to requirements for establishing an electrically-safe work condition (i.e. lockout/tagout) to achieve Mode 1.

Note: Verification of an electrically safe work condition with a voltage-rated instrument is covered by the Mode 1 process since the energy source has been de-energized, and is not considered Mode 2.

Mode 2 (energized diagnostics and testing):

Measurements, diagnostics, testing, and observation of equipment functions are conducted with the equipment energized and with some, or all, of the normal protective barriers, removed and interlocks bypassed. Mode 2 work involves the use of proper voltage-rated equipment to contact the energized conductors to measure, diagnose, and test energized equipment. If any portion of the worker's body passes the Restricted Approach Boundary, appropriate PPE for shock hazards must be worn. If any portion of the worker's body passes the Arc Flash Protection Boundary, appropriate arc flash PPE must be worn. Examples of Mode 2 operations include:

  • Making routine voltage measurements with a multi-meter on energized components;
  • Performing tests while working in close proximity to exposed energized components;
  • Following manufacturer's instructions for diagnostics and troubleshooting of energized circuits; and
  • Working on experimental facilities that operate in this mode.

Mode 3 (energized work):

The physical movement of energized conductors and parts, or moving parts that are near energized conductors (within the Prohibited Approach Boundary), and operations conducted with the equipment fully energized and with some, or all, of the normal protective barriers, removed. Work in this mode must be justified and conducted under close supervision and specific controls. Written approval is required if the thresholds for shock or arc-flash are exceeded.

Note 1: Mode 3 work is not permitted within the approach boundaries unless the risk is reviewed and determined to be justified, and subsequently approved by the Principal Investigator (professor providing oversight) and Environmental Health & Safety.

Note 2: Hazard classes noted in red or maroon shall be reviewed by the Principal Investigator and Environmental Health & Safety (where necessary) to ensure engineering controls implemented to reduce the risk to an acceptable level.


Students performing work on energized systems must be supervised by a qualified person (i.e. principal investigator), and must be trained on the hazards of electricity and the methods used to control or eliminate those hazards. Students must complete electrical safety training through EHS, as applicable, and may need additional information from their department regarding specific electrical apparatus and hazards involved.


Each department that performs electrical research covered by this program should assign duties outlined in this program to either a safety committee composed of qualified faculty and staff, the principal investigator, and/or the program/area supervisor, as appropriate, for the scope of departmental operations and conditions of use.

Principal investigator:

The principal investigator (PI) of the laboratory space(s) or operation(s) has responsibility for assuring compliance with all electrical safety requirements that pertain to maintaining a safe working environment and protecting laboratory employees, students, and visitors from injury or death as a result of electrical hazards. The PI has the responsibility to:

  • Ensure that work that impacts building electrical systems or the physical structure of the building complies with university Policy 5405. Work on building electrical supply systems must comply with the requirements of the National Electrical Code (NEC), Occupational Safety and Health Administration (OSHA) requirements, and the other recognized authorities.
  • Ensure that appropriate controls (e.g. safe work practices, work protocols, necessary training, hazard warnings, covers and insulation, appropriate personal protective equipment, etc.) are established and implemented as necessary.
  • Ensure the acceptability of experimental electrical wiring and apparatus. In this capacity the principal investigator will, as needed:
    • Review drawings, tests, and other documentation provided by project coordinators, staff, students, or other responsible parties for compliance with accepted safety criteria and code intent.
    • Consult with appropriate specialists to verify that engineering, design, and construction parameters have been correctly applied.
    • Inspect power systems and incidental wiring related to the experiment.
    • Conduct other inspections and analyses as necessary to verify the acceptability of the apparatus involved.
    • Evaluate existing workplace safety by inspecting or assisting in the inspections of their workplace for compliance with the safety requirements outlined in this policy as needed.

Environmental Health & Safety:

Environmental Health & Safety responsibilities for this program include:

  • Developing, implementing, and administering the program;
  • Training on the program requirements and maintaining centralized records;
  • Serving as a technical resource for application of program requirements;
  • Assisting with the risk assessment process in accordance with training and DOE-HDBK-1092-2013 (upon request);
  • Providing guidance on the selection of protective equipment; and
  • Evaluating the overall effectiveness of the program on a periodic basis and making appropriate changes as needed to assure the safety of personnel.

Involvement by Environmental Health & Safety does not relieve the departments, supervisors, or contractors of their individual responsibilities.


Departments are expected to maintain safe and healthy living, learning, and working environments for faculty, staff, students, and visitors to our campus.  

  • Each department performing energized electrical work must ensure that personnel assigned to such work are qualified, trained, provided with appropriate protective equipment, and are following approved procedures.  
  • Departments must ensure that all employees performing electrical research have attended appropriate training and are qualified to work on the project.  
    • To assist principal investigators in ensuring students are qualified to work on a project, refer to this guide.
  • Departments involved in electrical research must ensure that all projects are designed in compliance with accepted safety criteria and code intent. To facilitate compliance with these requirements, it is recommended that the department assign the duties outlined in this program to either a safety committee composed of qualified faculty and staff, the principal investigator, and/or the program supervisor as appropriate for the scope of departmental operations and conditions of use. The principal investigator and/or the program supervisor are responsible for assuring the acceptability of experimental electrical wiring and apparatus.
  • Departments must ensure that electrical systems and related equipment are maintained in a safe manner in order to protect employees, students, and the public from hazardous conditions. Unsafe electrical conditions should be reported to the Division of Campus Planning, Infrastructure, and Facilities immediately for correction at 540-231-4300.


Employees/students involved in electrical research projects involving electrical systems, equipment, or components greater than 50 volts (ac or dc) must:

  • Follow the requirements of this program;
  • Attend required training;
  • Wear assigned personal protective equipment; and
  • Know and respect the limitations of their technical skills and knowledge.


Where contractors may be involved in electrical research projects, they must comply with all local, state, and federal safety requirements, and must assure that all employees performing work on Virginia Tech property have been suitably trained and are provided appropriate personal protective equipment per the Safety Requirements for Contractors and Subcontractors Program

  • Training is available online, and is intended for personnel who perform electrical research operations, including voltage-testing/diagnostics, assembly, etc. Information regarding shock and arc-flash hazards are covered, risk assessment, and engineering and administrative controls to eliminate or reduce hazards found in the electrical research and development arena. Where personal protective equipment for arc-flash events is selected as hazard mitigation, Electrical Qualified Person training should also be completed.

Students involved in electrical research must receive information and training on the following:

  • How to recognize and avoid the electrical hazards that might be present with respect to the equipment or testing/research method, including skills and techniques necessary to determine the nominal voltage of exposed live parts by reading drawings, signs, and labels.
  • The proper use of the special precautionary techniques, personal protective equipment, including arc-flash, insulating and shielding materials, and insulating tools and test equipment,
  • The departmental internal review process necessary to ensure projects are designed safely and hazard controls are effective and appropriate, and
  • Actions to be taken in emergency situations, including first aid and cardio-pulmonary resusitation (CPR) training.
  • Electrical Qualified Person (classroom) training is intended for employees who perform electrical work tasks at greater than 50 volts as part of the duties, such as voltage-testing/diagnostics, repairs to electrical systems, new installations, etc. Information regarding shock and arc-flash hazards are discussed, as well as engineering and administrative controls, and the selection of appropriate personal protective equipment. Personnel involved with electrical research may need to complete Electrical Qualified Person level training in addition to Electrical Safety for Research if they will be exposed to more than 50 volts, and where appropriate electrical personal protective equipment is necessary. 

Electrical equipment, including electrical apparatus for research and development, must be free from recognized hazards that are likely to cause death or serious physical harm. Equipment must be suitable for installation and use and must be installed and maintained in accordance with the manufacturer’s instructions. Overloaded circuits, damaged wiring, and defective switches/outlets pose a potential fire hazard. Report any damage or defects to the Division of Campus Planning, Infrastructure, and Facilities for repair or replacement. 

The National Electric Code (NEC) is an installation code that provides adequate protection for people who use equipment or facilities.  Any installed electrical service or equipment that meets the requirements identified in the NEC will be safe while the equipment is operating normally, provided that it is adequately maintained.  Electrical installations must be in accordance with Virginia Tech's Office of the University Building Official.

If the equipment is not listed or labeled by a Nationally Recognized Testing Laboratory (NRTL), such as a custom-built research apparatus or equipment purchased from other countries, review, and approval must be completed.

Work performed on-premise wiring or wiring for connection to supply must meet current National Electric Code requirements regardless of who performs the work. Implementation, including interpretation, inspection, and enforcement of these code requirements is coordinated through the Office of the University Building Official.  Responsibility and costs associated with remediation may fall to the department creating the non-compliant condition.  

Live parts of electrical equipment operating at 50 volts alternating current (or 100 volts direct current) or more must be guarded against accidental contact by:

  • Use of an approved cabinet or other approved enclosure (ex. cover plates, circuit breaker blanks), 
  • Location in a room or vault that is accessible to qualified persons only, or 
  • Elevating the equipment, or 
  • Controlling the arrangement of the space to prevent contact by unqualified persons. 

If electrical equipment is located in an area where it is potentially exposed to physical damage or may fail as in the case of electrical research and development, the enclosure, location, or barrier must be sufficient enough to prevent such damage beyond the barrier.

Whenever possible, cord sets should be manufactured and listed by a nationally recognized testing laboratory. If job-made cord sets will be assembled by employees, the following requirements must be met.

Risk assessment for electrical research operations at Virginia Tech is based upon the Department of Energy's Handbook 1092-2013 and NFPA 70E-2021 (for traditional electrical hazards). There are hazard classification charts to cover 60 Hz, DC, capacitors, batteries, sub-RF, and RF power sources. It is possible that a system has more than one energy source. Hazard classification charts are available in the DOE handbook and are provided during Environmental Health and Safety Electrical Safety for Research training. Charts and tables for more traditional electrical work are available in Environmental Health & Safety's Electrical Qualified Person training. Depending on the nature of the research project, both trainings may be beneficial.

Students, in conjunction with their professor and/or Lab Manager, should determine the hazard class for each power source present in the research apparatus. The hazard class will then be used to determine appropriate guidance for the mode of operations being performed at any given time.

Refer to the various thresholds listed in this section. If the thresholds are crossed, appropriate hazard controls and/or personal protective equipment will be necessary as defined per the hazard class.

If an electrical shock or arc flash threshold is exceeded (by the design of the system/equipment/components) or crossed by personnel in proximity to exposed, energized electrical component, hazard controls must be implemented to eliminate or reduce exposure to an acceptable level. Where the risk cannot be eliminated or reduced to an acceptable level, electrical personal protective equipment must be selected for the voltage and incident energy expected and worn by qualified personnel who are working within the approach boundaries.

In research and development, conditions and controls found in a typical electrical system may be temporarily removed or not within the scope of the project. For example, covers and barriers may be removed from energized systems exposing personnel to a shock hazard. Electrical shock can be fatal. The following thresholds for defining shock hazards are to be observed in research and development applications.





60 Hz

> 50 V and > 5 mA



> 100 V and > 40 mA







> 100 V and > 1 J, or

> 400 V and > 0.25 J



> 100 V


1 Hz - 3 kHz

> 50 V and > 5 mA


3 kHz - 100 MHz

A function of frequency

Arc flash burns may be caused by electric arcs, and are similar to any other heat burn; however, arc-blast hazards (at much greater energy potential resulting in serious injury or death) may be present during research and development applications. Arc-blasts occur rapidly and can result in significant injury or death, as well as equipment destruction. The following arc-flash thresholds are to be observed in research and development applications.

Source Includes Thresholds
AC 60 Hz

<240 V and the transformer supplying the circuit is rated > 125 kVA.

< 240 V and the circuit is supplied by more than one transformer.

> 240 V

DC All > 100 V and > 500 A
Capacitors All > 100 V and > 10 kJ
Batteries All > 100 V and > 500A
Sub-RF 1 - 3 kHz > 250 V and > 500 A

When these boundaries are crossed, hazard controls appropriate for the risk category must be implemented. Risk categories are determined via tables and charts provided in DOE-HDBK-1092-2013, Appendix D. This information is covered during training. Risk categories include: "no hazard, "little to no hazard," "injury or death could occur by close proximity or contact," "injury or death could occur by proximity or contact," or a "high level of risk where significant engineering and administrative controls are necessary to manage the hazard."


For each power source present in the research apparatus (that exceeds the noted threshold above), a subclass must be identified (provided in the Environmental Health & Safety Electrical Safety for Research training), and subsequent controls must be implemented. Controls for each subclass are based upon the Mode of Operation (covered in "Electrical work") to be performed.


In addition to proper electrical training, the following controls may be required to eliminate or significantly reduce the associated risks with electrical research activities.

Isolation and distance can eliminate potential exposure to electrical hazards, or reduce the risk to an acceptable level. These options should always be considered when the threshold is reached or exceeded. Examples of isolation and distance include:

  • Control rooms designed for electrical apparatus testing when the potential risk is significant;
  • Shielding;
  • Personnel located outside of approach boundaries; and/or
  • Remote sensors and testing/diagnostic equipment.

Higher risk energized work may require a second person to be present, known as the "two-person rule" or "buddy system." The second person must also be "qualified," and must understand the work activities and hazards present. This person must be trained to know what to do in case of an electrical incident involving the other worker, including the location of electrical disconnects, information for contacting emergency services, and first aid/CPR/AED response.

In some instances, a "safety watch" is necessary. The use of a safety 2atch is more stringent than the two-person rule. Safety watch responsibilities and qualifications include:

  • Training in methods of the release of victims from contact with electrical energy, cardiopulmonary resuscitation (CPR), and the use of automated external defibrillators (AED);
  • Thorough knowledge of location and operation of emergency shutdown push buttons and power disconnects;
  • Thorough knowledge of the specific working procedures to be followed and the work to be done;
  • Monitoring the work area for unsafe conditions or work practices, and taking necessary action to ensure abatement;
  • De-energizing equipment and alerting emergency rescue personnel as conditions warrant;
  • Maintaining visual and audible contact with personnel performing the work;
  • Removal of injured personnel, if possible;
  • Preventing unqualified persons from crossing the established safe approach boundaries; and
  • No other duties may preclude observing and rendering aid.

Work controls, as recommended in the risk assessment, may include documented standard operating procedures (SOP) for hazardous electrical research work. The SOP should include specific steps to be taken in order to energize the apparatus, run the test, and de-energize the apparatus. It should also include the results of the risk assessment, including the hazard class, controls to be implemented for modes of operation involving a potential exposure to electrical hazards, approach boundaries, and specific personal protective equipment to be worn. A schematic of the system should be included, which identified the various components and their magnitudes (voltages, pressures, temperatures, etc.). Documentation from the department regarding reviews and approvals must be made available upon request.

An Energized Electrical Work Permit (EEWP), or equivalent written approval from the lab manager/principal investigator, must be completed and approved where the task is not specifically exempt from written approval (e.g. voltage-testing or diagnostics), and where the system must be energized and approach boundaries will be crossed. Work performed under energized conditions is generally prohibited, but may be considered where a power source physically cannot be de-energized (i.e. batteries). Elimination (of the electrical hazard to personnel) and engineering controls must be considered and implemented, where feasible before energized work is approved by three levels of management and permitted.

Personal protective equipment:

Appropriate voltage-rated PPE must be worn when crossing the Limited and Restricted Approach Boundaries. Voltage-rated gloves must be maintained in accordance with OSHA and the manufacturer's instructions.

Appropriate arc-rated PPE must be worn when crossing the Arc-Flash Protection Boundary. Recommendations for arc-rated clothing are based upon the potential incident energy for specific systems and tasks. Personnel wearing arc-rated clothing must be trained in the proper use, care, and limitations.

Review the information on electrical PPE, or attend Electrical Qualified Person training.

Job-made cords are considered by OSHA to be temporary wiring extensions of the branch circuit. The following special requirements apply:

  • Job-made cord sets must be assembled by a qualified person.
  • The completed assembly must be inspected by a qualified person before the cord set is used initially. The following checks and tests (or equivalent) should be performed:
    • Determine that all equipment grounding conductors are electrically continuous.
    • Test all equipment grounding conductors for electrical continuity.
    • Determine that each equipment grounding conductor is connected to its proper terminal.
    • Test each receptacle and attachment plug to ensure correct attachment of the equipment grounding conductor.
  • The cords may be of a class less than that required for a permanent installation.
  • Temporary installations are permitted during the period of construction, remodeling, maintenance, repair, or demolition of buildings, structures, and equipment or similar activities.
  • Temporary installations must be removed immediately upon completion of the work for which the wiring was installed.
  • Job-made cords are considered to be in compliance with OSHA standards (as opposed to listing by a nationally recognized testing laboratory for manufactured sets) provided they are assembled in a manner equivalent to those that are factory-assembled and approved. Criteria include:
    • All components must be approved for the purpose of a nationally recognized testing laboratory.
    • Individual components must be compatible for use with the other components of the completed assembly.
    • The cord set must be marked appropriately with the manufacturer name or trademark, voltage, current, wattage, or other information as needed.
    • Boxing intended for use in a permanent installation may not be used.
    • Connections to devices and fittings must provide strain relief.
    • Cords passing through enclosures must be protected by bushings or fittings designed for the purpose. Fittings designed to fasten cables to metal boxes are not acceptable.
    • Grounded conductor must not be attached to any terminal or lead so as to reverse designated polarity.

The following requirements apply to the use of cord-and-plug-connected equipment and flexible cord sets (extension cords):

  • Extension cords may only be used to provide temporary power.
  • Portable cord-and-plug connected equipment and extension cords must be visually inspected before use on any shift for external defects such as loose parts, deformed and missing pins, or damage to outer jacket or insulation, and for possible internal damage such as pinched or crushed outer jacket. Any defective cord or cord-and-plug-connected equipment must be removed from service and no person may use it until it is repaired and tested to ensure it is safe for use.
  • Extension cords must be of the three-wire type (except as specifically allowed by the NEC). Extension cords and flexible cords must be designed for hard or extra-hard usage (for example, types S, ST, and SO). The rating or approval must be visible.
  • Job-made extension cords may comply with the following requirements.
  • Personnel performing work on renovation or construction sites using extension cords or where work is performed in damp or wet locations must be provided and must use, a ground-fault circuit interrupter (GFCI).
  • Portable equipment must be handled in a manner that will not cause damage. Flexible electric cords connected to equipment may not be used for raising or lowering the equipment.
  • Extension cords must be protected from damage. Sharp corners and projections must be avoided. Flexible cords may not be run through windows or doors unless protected from damage, and then only on a temporary basis. Flexible cords may not be run above ceilings or inside or through walls, ceilings, or floors, and may not be fastened with staples or otherwise hung in such a fashion as to damage the outer jacket or insulation.
  • Cords must be covered by a cord protector or tape when they extend into a walkway or other path of travel to avoid creating a trip hazard.
  • Extension cords used with grounding-type equipment must contain an equipment-grounding conductor (i.e., the cord must accept a three-prong, or grounded, plug).
  • Attachment plugs and receptacles may not be connected or altered in any way that would interrupt the continuity of the equipment grounding conductor. Additionally, these devices may not be altered to allow the grounding pole to be inserted into current connector slots. Removing the grounding prong from an electrical plug is prohibited.
  • Flexible cords may only be plugged into grounded receptacles. The continuity of the ground in a two-prong outlet must be verified before use with a flexible cord, and it is recommended that the receptacle be replaced with a three-prong outlet as allowed by the NEC. Adapters that interrupt the continuity of the equipment grounding connection may not be used.
  • All portable electric equipment and flexible cords used in highly conductive work locations, such as those with water or other conductive liquids, or in places where employees are likely to contact water or conductive liquids, must be approved for those locations.
  • Employees' hands must not be wet when plugging and unplugging flexible cords and cord-and-plug connected equipment if energized equipment is involved.
  • If the connection could provide a conducting path to employees' hands (for example, if a cord connector is wet from being immersed in water), the energized plug and receptacle connections must be handled only with insulating protective equipment.
  • Locking-type connectors must be properly locked into the connector.
  • Lamps for general illumination must be protected from breakage, and metal shell sockets must be grounded.
  • Temporary lights must not be suspended by their cords unless they have been designed for this purpose.
  • Portable lighting used in wet or conductive locations, such as tanks or boilers, must be operated at no more than 12 volts or must be protected by ground-fault circuit interrupters (GFCI's).

Power strips with circuit breaker (overcurrent) protection may be used in place of extension cords on a more permanent basis. Power strips are available with cords up to 15 feet long to provide greater flexibility in providing receptacles where needed. Power strips must be plugged directly into premise wiring (i.e. wall outlets or receptacles). Power strips may only be used in accordance with the manufacturer's recommendations, and one power strip may not be plugged into another power strip - known as "daisy chaining."

In most cases, proper insulation and effective grounding prevent injury from electrical wiring systems or equipment. However, there are instances when these methods do not provide the degree of protection required. Ground-fault circuit-interrupters (GFCI) are designed to protect people from electrical shock. They are not overcurrent devices like fuses or circuit breakers. GFCIs sense an imbalance in current flow over the normal path. If the current flowing differs more than 5 milliamperes between the hot and neutral wires, the GFCI will open the circuit in approximately 1/40 of a second, greatly reducing the likelihood of a serious shock to any person in the circuit. The GFCI "assumes" that the leaking current on the circuit is flowing in an abnormal path (i.e. ground fault), which could be you!

Types of GFCIs:

There are three basic types of GFCIs:

  • Circuit-Breaker GFCIs - These GFCIs function as a standard circuit breaker with the additional functions of a GFCI. They are direct replacements for standard circuit breakers of the same rating.
  • Receptacle GFCIs - One or more receptacle outlets are protected by the GFCI because GFCIs protect the circuit "downstream" from its location in the system.
  • Portable GFCIs - "Pigtails" are designed to be easily transported from one location to another, such as use with extension cords, power tools, and equipment.

Required use:

GFCIs must be used in the following situations:

  • Wet or damp locations where water could possibly enter the housing of power tools or equipment and shock the person in contact with it;
  • Construction sites; and
  • Renovation projects.

Some examples of where GFCIs would provide additional protection include:

  • When using double-insulated hand tools in wet/damp locations where water could possibly enter the tool housing and cause a shock.
  • Using extension cords with portable equipment, which are often exposed to physical damage.


GFCIs have a built-in test circuit, which imposes an artificial ground fault on the load circuit to assure the protection is still functioning properly. You should follow the manufacturer's instructions for testing the device being used. The tests should be performed on a regular basis.

  • Monthly for permanently wired devices, such as the circuit breaker or receptacle types.
  • Prior to use for temporary portable types, such as "pigtails."

Large capacitor hazards:

Capacitors may store hazardous energy even after the equipment has been de-energized, and may build up a dangerous residual charge without an external source. "Grounding" capacitors in series, for example, may transfer (rather than discharge) the stored energy. Another hazard exists when a capacitor is subjected to high currents that may cause heating and explosion. Capacitors may be used to store large amounts of energy. An internal failure of one capacitor in a bank frequently results in an explosion when all other capacitors in the bank discharge into the fault.

Note: High voltage cables should be treated as capacitors because they have capacitance and thus can store energy.

The liquid dielectric in many capacitors, or its combustion products, may be toxic.

Automatic discharge:

Use permanently connected bleeder resistors when practical. Capacitors in series should have separate bleeders. Automatic-shorting devices that operate when the equipment is de-energized, or the enclosure is opened, must be used. The time required for a capacitor to discharge to a safe voltage (50 volts or less) must not be greater than the time needed for personnel to gain access to voltage terminals. In no case must it be longer than 5 minutes.

In the case of equipment with stored energy in excess of 5 J, an automatic, mechanical-discharging device must be provided that functions when normal access ports are opened. This device must be contained locally within a protective barrier to ensure wiring integrity and should be in plain view of the person entering the protective barrier so that the individual can verify its proper functioning. Protection also must be provided against the hazard of the discharge itself.

Safety grounding:

Provide fully visible, manual-grounding devices to render the capacitors safe while they are being worked on. Clearly mark grounding points and use caution to prevent transferring charges to other capacitors.

All grounding hooks must:

  • Have crimped and soldered conductors.
  • Be connected such that impedance is less than 0.1 (omega) to the ground.
  • Have the cable conductor clearly visible through its insulation.
  • Have a cable conductor size of at least #2 extra flexible, or in special conditions, a conductor capable of carrying any potential current.
  • Be insufficient number to conveniently, and adequately, ground all designated points.
  • Be grounded and stored in the immediate area of the equipment in a manner that ensures they are used.

In equipment with stored energy in excess of 5 J, a discharge point with an impedance capable of limiting the current to 500 A or less should be provided. This discharge point must be identified with a yellow circular marker with a red slash and must be labeled "HI Z PT" in large, readable letters. A properly installed grounding hook must first be connected to the current-limiting discharge point and then to a low-impedance discharge point (less than 0.1 (omega)) that is identified by a yellow circular marker. the grounding hooks must be left on all of these low-impedance points during the time of safe access. The low-impedance points must be provided, whether or not the HI Z current-limiting points are needed. Voltage indicators that are visible from all normal entry points should also be provided.


Capacitors used in parallel should be individually fused when possible to prevent the stored energy from dumping into a faulted capacitor. Care must be taken in the placement of automatic-discharge safety devices with respect to fuses. If the discharge will flow through the fuses, a prominent warning sign must be placed at each entry indicating that each capacitor must be manually grounded before work can begin. Special knowledge is required for high-voltage and high-energy fusing.

Unused terminal shorting:

Terminals of all unused capacitors representing a hazard, or capable of storing 5 J or more, must be visibly shorted.

This section describes inductors and magnets that can store more than 5 J of energy or that operate at 50 V or more. The following are some hazards peculiar to inductors and magnets:

  • The ability of an inductor to release stored energy at a much higher voltage than that used to charge it.
  • Stray magnetic fields that attract magnetic materials.
  • Time-varying stray fields induce eddy currents in conductive material thereby causing heating and mechanical stress.
  • Time-varying magnetic fields that may induce unwanted voltages at inductor or magnet terminals.

Safety practices:

  • Automatic Discharge. Use freewheeling diodes, varistors, thyrites, or other automatic shorting devices to provide a current path when excitation is interrupted.
  • Connections. Pay particular attention to connections in the current path of inductive circuits. Poor connections may cause destructive arcing.
  • Cooling. Many inductors and magnets are liquid-cooled. The unit should be protected by thermal interlocks on the outlet of each parallel coolant path, and a flow interlock should be included for each device.
  • Eddy Currents. Units with pulsed or varying fields must have a minimum of eddy-current circuits. If large eddy-current circuits are unavoidable, they should be mechanically secure and able to safely dissipate any heat produced.
  • Grounding. Ground the frames and cores of magnets, transformers, and inductors.
  • Rotating Electrical Machinery. Beware of the hazards of residual voltages that exist until rotating electrical equipment comes to a full stop.

Control and instrumentation:

Proactive safety culture is vital to the safe design of most control applications. The following checklist should be used as a guide.

  • Checkout. Check interlock chains for proper operation after installation, after any modification, and during periodic routine testing.
  • Fail-safe design. Design all control circuits to be "fail-safe." Starting with a breaker or fuse, the circuit should go through all the interlocks in series to momentary on-off switches that energize and "seal in" a control relay. Any open circuit or short circuit will de-energize the control circuit and must be reset by an overt act.
  • Interlock bypass safeguards. Establish a systematic procedure for temporarily bypassing interlocks. A follow-up procedure should be included to ensure the removal of the bypass as soon as possible. When many control-circuit points are available at one location, the bypassing should be made through the normally open contacts of relays provided for this purpose. In an emergency, these relays can be opened from a remote control area.
  • Isolation. Isolate control power from higher power circuits by transformers, contactors, or other means. Control power should be no more than 120 V, ca, or dc. All circuits should use the same phase or polarity so that no hazardous additive voltages are present between control circuits or in any interconnecting system. Control-circuit currents should not exceed 5 A.
  • Lock-out. Use a keyed switch in interlock chains to provide positive control of circuit use. To ensure power removal before anyone enters the enclosure, this same key should also be used to gain access to the controlled equipment.
  • Motor control circuits. Motor circuits must have a positive disconnect within view of the motor or, if this is not practical, a disconnect that can be locked open by the person working on these motor circuits.
  • Overvoltage protection. Control and instrumentation circuits used with high-voltage equipment must have provision for shorting fault-induced high voltages to the ground. High-voltage fuses with a high-current, low-voltage spark gap downstream from the high-voltage source are recommended. This also applies to all circuits penetrating high-voltage enclosures.
  • Voltage divider protection. The output of voltage dividers used with high voltages must be protected from overvoltage-to-ground within the high-voltage area by spark gaps, neon bulbs, or other appropriate means.
  • Current monitors. Measure currents with a shunt that has one side grounded or with current transformers that must be either loaded or shorted at all times.
  • Instrument accuracy. Check instrumentation for function and calibration on a routine basis.

Primary disconnect:

Provide a lockable means of positively disconnecting the input on large power supplies (most Class 2A-, 3A-, and 3B-rated units). See Table 1 and Table 2. This disconnect must be clearly marked and accessible. If provided with a built-in lock that is part of an interlocking chain, the key must not be removable unless the switch or breaker is in the "off" position.

Overload protection:

Overload protection must be provided on the input and should be provided on the output.

Floating power supplies:

Some research equipment (e.g. electrophoresis devices, x-ray tubes, and ion-bombardment power supplies) employ ungrounded (floating) power supplies. This equipment may operate in voltages ranging from 50 volts to kilovolts with output capacities in excess of 50 mA, and must be considered a lethal electrical hazard. Users of such equipment must take special precautions to minimize electrical hazards. Follow all manufacturer's instructions for equipment use, testing, and training. The following general guidelines also apply:

  • Locate equipment away from water and large metal areas.
  • Do not use connectors and jack fittings that allow accidental skin contact with energized parts.
  • Interlock readily accessible enclosures.
  • Use non-metallic secondary containment if liquids or gels are involved.
  • Verify the power supply is floating when commissioning and recommissioning the equipment at least once a year.


Once the hazard/risk category has been identified, either from NFPA 70E tables or an arc flash analysis, appropriate protective clothing can be selected. Protective clothing includes flame-resistant (FR) shirts, pants, coveralls, jackets, arc flash protective hoods and suits, eyewear, and head protection. The protective clothing selected for the corresponding hazard/risk category number shall have an appropriate arc rating for the hazard/risk category.


Materials that have an established arc flash rating (ATPV expressed in cal/cm2) are permitted to be used either alone or in combination with materials without an established rating.  Layering increases the overall protective characteristics of FR clothing. 

  • Outer layers should be made of FR material, especially when used in conjunction with ignitable or meltable clothing, such as a rain suit.
    • FR rainwear is now available.
    • The outer layers must limit the temperature rise of the ignitable underlayers to no more than 1.2 cal/cm2. 
  • Underlayers should be made of non-melting, natural fiber materials, such as untreated cotton, wool, rayon, silk, or blends of these materials. Meltable fibers such as acetate, nylon, polyester, polypropylene, and spandex shall not be permitted in underwear next to the skin.
    • Incidental amounts of elastic used in non-melting fabric underwear or socks are permitted.

Coverage and fit:

Clothing should cover all potentially exposed areas as completely as possible. Shirt sleeves should be fastened at the wrist and shirts and jackets shall be closed at the neck. Clothing should be loose-fitting to provide additional thermal insulation from the air space between layers and reduce the conduction of heat from the FR clothing to skin; however, it should fit properly (i.e. not so loose that it interferes with the work task).

Arc flash suits:

Arc flash suits must be designed to meet all applicable ANSI and ASTM standards and shall have an arc rating. Safety glasses are required to be worn beneath face shields or hoods. Goggles should not be worn because they are permitted by ANSI to have an ignitable and meltable component.

FR clothing and arc flash suits must be inspected before each use for contamination or damage that could affect the protective qualities of the fabric, such as grease, oil, flammable or combustible liquids spills, or tears.  Never use contaminated or damaged protective equipment. Care and maintenance per the manufacturer’s instructions must also be followed in order to maintain the protective properties. A simplified clothing system provides minimum protection for electrical workers in addition to other required personal protective equipment recommended for the specific task.

Everyday Work Clothing

Appropriate for Hazard/Risk Category Tasks 1, 2, and 2*

Arc Flash Suit

Appropriate for Hazard/Risk Category Tasks 3 and 4

FR long-sleeve shirt with FR pants or FR coveralls with a minimum arc rating (ATPV) of 8 cal/cm2

A total clothing system consisting of FR shirt and pants and/or FR coveralls and/or arc flash coat and pants with a minimum arc rating (ATPV) of 40 cal/cm2

Voltage-rated gloves. The hands are probably the most exposed part of a worker’s body since they are the closest to the hazard. Voltage-rated gloves with leather protectors are required to be worn as appropriate for the task (see chart). Gloves must be tested by a third party before the first issue and every 6 months thereafter.

Class Max. Use Voltage AC Max. Use Voltage DC
00 500 750
0 1,000 1,500
1 7,500 11,250
2 17,000 25,500
3 26,500 39,750

Foot protection:

Heavy-duty leather work shoes provide some arc flash protection to the feet and shall be used in all tasks in hazard/risk category 2 and above.

Electrical protective tools and equipment:

When working inside the Limited Approach Boundary, workers must select and use work practices, including insulated tools that provide maximum protection from a release of energy. If contact with the exposed live part is likely, the worker must only use insulated tools.

Insulated tools must be rated for the voltages on which they are used, and they must be designed and constructed for the environment to which they are exposed and the manner in which they are used.

Fuse or fuse holding equipment must be insulated for the circuit voltage and shall be used to remove or install a fuse if the fuse terminals are energized.  In an industrial setting, fuses should not be installed or removed energized.  Where fuses are removed in an emergency, the fuse-handling equipment must be rated for the voltage. 

  • Fuses that are mounted on poles and removed and installed by using a “hot stick” may be exchanged routinely with the fuse terminals energized. 

Ropes and handlines used near exposed live parts operating at 50 volts or more, or used where an electrical hazard exists, shall be nonconductive.

Fiberglass-reinforced plastic rods and tubes used for live line tools shall meet ASTM 711 requirements.

Portable ladders used near exposed live parts operating at 50 volts or more, or where an electrical hazard exists, shall have nonconductive side rails and meet ANSI standards.

Protective shields, protective barriers, or insulating materials shall be used to protect each employee from shock, burns, or other electrically related injuries while working near live parts that might accidentally be contacted, or where dangerous electric heating or arcing might occur.  When normally enclosed live parts are exposed for maintenance or repair, they shall be guarded to protect unqualified persons from contact with the live parts.

Rubber insulating equipment, such as line hose, covers, blankets, or sleeves used for protection from accidental contact with live parts shall meet applicable ASTM standards.  It must be tested by a third party as follows:

Type of Rubber Insulated Equipment

Testing Intervals

Line hose

Upon indication that the insulating value is suspect.


Upon indication that the insulating value is suspect.


Before first issue and every 12 months thereafter.


Before first issue and every 12 months thereafter.

Note:  If the insulating equipment has been electrically tested but not issued for service, it may not be placed into service unless it has been electrically tested within the last 12 months.

Elimination of potential energy sources is the primary control for electrical hazards and should be the first consideration when electrical systems are energized at 50 volts or more. An electrically safe work condition (i.e. lockout/tagout) may not be feasible for voltage-testing and diagnostic tasks, in which case administrative controls and appropriate personal protective equipment are required to reduce or minimize the extent of injury in the event of an incident.

It is important to realize, however, that the acts of opening a disconnecting means, measuring for the absence of voltage, visually verifying a physical break in the power conductors, and installing safety grounds all contain some degree of risk because of the potential for an arc-flash event to occur. These acts are all necessary to achieve an electrically safe work condition, and until they are completed, the worker should be wearing personal protective equipment based on the risk assessment conducted. 

To achieve an electrically safe work condition, the requirements of Virginia Tech’s Lockout/Tagout Program must be followed. Personnel performing electrical work must attend Environmental Health & Safety Lockout/Tagout Authorized Person training, which addresses hazardous energy sources, general lockout/tagout procedures, when specific written lockout/tagout procedures are required, and program guidelines.

Electrical systems and equipment in large facilities rarely stay the same for more than a few months or years. Electrical energy sources are sometimes difficult to identify, especially when the path of circuit conductors is not easily observed or historical work on the system has created questionable standards of practice or compliance. 

Up-to-date drawings should be maintained on electrical systems and equipment and updated as necessary when changes are made. This is often a difficult task, but it is imperative to effectively communicate detailed information to personnel and contractors. Labels are another means of identifying and communicating information, but they must be complete and accurate as well. Inaccuracies identified should be reported to the Division of Campus Planning, Infrastructure, and Facilities immediately for correction.     

Operating "adequately rated disconnecting means" is the next step in creating an electrically safe work condition. Energy-isolating devices establish a positive break in the conductors supplying energy. Simply operating an on/off control device is not sufficient to disconnect electrical equipment or circuits. The system must then be tested for the absence of voltage. For knife-style disconnects especially, the cover should be opened to visually inspect and verify that all phase conductors have opened.  Poles sometimes fail to open. Sometimes the handle of the energy-isolating device moves, but all the poles remain closed. If the physical break in the power conductors is hidden from view, the worker must assume that an electrically safe work condition has not been established and he/she may therefore be exposed to energized electrical conductors. When exposed to energized electrical conductors, appropriate protective equipment must be used.

Voltage testing must be conducted to verify the absence of voltage. Testing devices are considered safety equipment and must meet the minimum requirements necessary to measure the expected (possible) voltage. Minimum requirements for test instruments, equipment, and their accessories shall include:

  • Appropriately rated for circuits and equipment to which they will be connected;
  • Appropriately designed for the environment to which they will be exposed, and for the manner in which they will be used; and
  • Properly inspected for external defects and damage prior to use each day.

A person’s life frequently depends on the effectiveness of the voltmeter and using it effectively. Therefore, the device should be of high quality, listed or labeled by a Nationally Recognized Testing Laboratory, protected from damage, inspected frequently, and treated with respect. If a cover of electrical equipment has been removed, then the worker is potentially exposed to electrical conductors and circuit parts that are likely energized. When exposed to energized electrical conductors, appropriate protective equipment must be used in conjunction with the test equipment for the hazards involved with the particular task.

It is necessary to verify the integrity of the voltage-testing device. Satisfactory operation on a known source of voltage should be established first. Then the worker should check for the presence of voltage on all conducting components of the equipment to be worked on. Lastly, the testing device should again be verified on a known voltage source. If the device still functions normally and the absence of voltage was verified, the equipment can be considered to be de-energized.

Temporary grounds should be used and properly installed to provide a convenient path for voltage unintentionally generated or flowing through the conductor while it is being worked on under specific conditions. Grounds should be installed in such a manner as to create a zone of equipotential around the worker to ensure an electrically safe working condition. The use of temporary grounds has little direct impact on the de-energized condition. They are intended to drain “unexpected” voltage due to capacitance, transformer action, shorts, or atmospheric static discharge away from the work area. Common examples of when temporary grounds are necessary to work on equipment or systems include:

  • Outside overhead lines, which can be re-energized by any number of sources and 
  • Shielded cables installed underground, in a cable tray, or in conduit.

Due to the possibility of large amounts of current flow on the temporary ground, and the need for the ground to remain in place in the event of such current flow, temporary grounds must be constructed per ASTM F 855. Job-made grounds should be avoided due to improper design and materials being used. Temporary grounds must have a fault-duty rating at least equal to the available fault-current capacity at the point in the circuit where it will be installed. Inadequately rated grounds can result in magnetic forces breaking the conductor or connector and whipping it around like a bullwhip.

All grounding clusters that are installed must be removed when the work task is completed. Each one should be assigned a unique identifier, which is recorded when installed. The same record should be reviewed when the grounding cluster is removed.

All equipment/material shall conform to the latest issue of all applicable standards as established by National Electrical Manufacturer's Association (NEMA), American National Standards Institute (ANSI), and Underwriters' Laboratories, Incorporated (UL) or other Nationally Recognized Testing Laboratories (NRTL) currently listed with the United States Department of Labor. All equipment and material, for which there are NEMA, ANSI, UL, or other NRTL standards and listings (see, shall bear the appropriate label of approval for the use intended.

If electrical equipment is not listed or labeled as outlined above, the department making the purchase shall have a review of the equipment be done for conformance with the National Electrical Code (NEC) and any applicable standards by either a testing laboratory, licensed electrical engineer or comparable authority, or licensed electrician for simpler systems. Such reviews are to be performed in accordance with NFPA 791 and NEC section 110. Any deficiencies identified during this review must be corrected before the equipment is placed in service. A written certification or test report that the equipment is safe to operate must be provided to and maintained by the department. If the equipment is plug-and-cord connected, a copy is to be provided to Environmental Health and Safety. If the equipment will be hard-wired to the building electrical system, a copy shall be provided to the University Building Official. All costs associated with such testing and inspections are the responsibility of the department making the purchase.

Approved: Acceptable to the authority having jurisdiction, which can include an approval process that includes listed and labeled equipment.

Arc-flash protection boundary: When an arc flash hazard exists, an approach limit from an arc source at which incident energy equals 1.2 cal/cm2 (5 J/cm2).

Arc-rating/ATPV: Arc-thermal performance value refers to the arc rating of flame resistant clothing, expressed in calories per square centimeter (cal/cm2).

Balaclava: An arc-rated hood that protects the neck and head, except for the facial area of the eyes and nose (similar to a ski mask).

Bare-hand work: A technique of performing work on live parts, after the employee has been raised to the potential of the live part.  The expertise necessary to perform this type of work can be acquired only by specialized training.

Barricade: A physical obstruction such as tape, cones, or A-frame-type wood or metal structures intended to provide a warning, and to limit access (to a work area with a hazard, such as exposed, energized electrical components).

Disconnecting means: A rated device, or group of devices or other means, by which the conductors of a circuit can be disconnected from their source of supply (i.e. circuit breakers, rated switches, fuses).

Department of Energy (DOE): The United States Department of Energy.

Diagnostic (testing): See definition for "working on."

Electrical hazard: A dangerous condition such that contact or equipment failure can result in electric shock, arc flash burn, thermal burn, or arc blast injury.

Electrically-safe work condition (ESWC): A state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.

Enclosure: The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts, or to protect the equipment from physical damage.

Energized: Electrically connected to or having a source of voltage.

Energized electrical work permit (EEWP): A formal process for risk assessment and management review of requests to work on energized electrical components, other than diagnostic/testing, where an Electrical Safe Working Condition (ESWC) cannot be established.

Exposed: The circuit is in such a position that, in case of failure of supports or insulation, contact with another circuit may result.

Exposed (to live parts): Capable of being inadvertently touched or approached nearer than a safe distance by a person.  It is applied to parts that are not suitably guarded, isolated, or insulated.

Exposed (wiring): On or attached to the surface or behind panels designed to allow access.

FR (flame-resistant) clothing: The property of a material whereby combustion is prevented, terminated, or inhibited following the application of a flaming or non-flaming source of ignition, with or without subsequent removal of the ignition source. FR clothing will have an ATPV expressed in cal/cm2, which can be related to the hazard/risk category. Examples include flame-retardant treated cotton, meta-aramid, para-aramid, and poly-benzimidazole fibers.

Ground fault: An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

Guarded: Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to a point of danger.

Hazard/risk category: A rating 1 through 4 indicating the seriousness of the electrical exposure, with 4 being the most serious.  Hazard/risk analysis considers both shock and arc flash hazards. Table 130.7(C)(9)(A) is used to relate work tasks to a hazard/risk category rating.

Incident energy: The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. One of the units used to measure incident energy is calories per centimeter squared (cal/cm2).

Insulated: Separated from other conducting surfaces by a dielectric (including air space) offering high resistance to the passage of current.

Insulated (tools): The tool manufacturer has assigned a voltage rating to the insulating material.

Isolated (as applied to location): Not readily accessible to persons unless special means for access are used.

Labeled: Equipment or materials to which has been attached a label, symbol, or another identifying mark of an organization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner. For example, UL (Underwriter’s Laboratories) or CSA (Canadian Safety Association).

Limited approach boundary (LAB): An approach limit at a distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists.

Listed: Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with the evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation or services, and whose listing states that the equipment, material, or services either meets appropriate designated standards or has been tested and found suitable for a specified purpose.

Live parts: Energized conductive components.

Meltable clothing: Clothing made from flammable synthetic materials that melt at temperatures below 600ºF, such as acetate, nylon, polyester, polypropylene, and spandex, either alone or in blends. Not permitted to be used when exposed to live electrical hazards.

Mode 1: All (research) operations are conducted in a positively de-energized (i.e. "cold") state. 

Mode 2: All (research) manipulative operations of uninsulated parts are conducted with the equipment in a positively de-energized state. When measurements and observation of equipment functions are necessary, the equipment is energized (i.e. "cold to hot") and some, or all, protective barriers are removed and interlocks bypassed. 

Mode 3: All (research) manipulative operations are conducted with the equipment fully energized and some or all normal protective barriers removed (i.e. "hot").

Natural fiber clothing: Clothing made from non-melting flammable materials, such as cotton, wool, rayon, or silk. This type of clothing is permitted for hazard/risk categories 0 and 1 provided the flash hazard analysis is 2.0 cal/cm2 or less, and that the fabric will not ignite and continue to burn under the arc exposure hazard conditions to which it will be exposed. Note that these fabrics could ignite and continue to burn on the body, resulting in serious burn injuries; however, clothing that does not melt may be used for low-level arc flash exposures.

Qualified person: A person trained and knowledgeable of the construction and operation of equipment or a specific work method and be trained to recognize and avoid the electrical hazards that might be present with respect to that equipment or work method. 

Repair: See definition for "working on."

Restricted approach boundary (RAB): An approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock due to electrical arc-over combined with inadvertent movement.

Shock hazard: A source of possible injury or damage to health associated with current through the body caused by contact or approach to energized electrical conductors or circuit parts.

Switch, isolating: A switch intended for isolating an electric circuit from the source of power. It has no interrupting rating, and it is intended to be operated only after the circuit has been opened by some other means.

Unqualified person: A person who might be exposed to electrical hazards and must be trained to understand how the exposure could occur and how to avoid injury. Examples include office workers, janitors, equipment operators, apprentices, or workers from crafts other than electrical.

Ventricular fibrillation (V-fib): An abnormal heart rhythm that commonly occurs during heart attacks. The ventricles of the heart are quivering instead of beating rhythmically. 

Voltage, nominal: A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g. 120/240 volts, 480Y/277 volts, 600 volts).

Voltage-rated: The maximum use voltages for rubber insulated equipment, such as gloves or sleeves.

Class of Equipment

Maximum Use Voltage
a-c – rms



0 1,000









Working distance: The distance between a person's face and chest area and a prospective arc source.

Working on: Intentionally coming in contact with energized electrical conductors or circuit parts with the hands, feet, or other body parts, with tools, probes, or with test equipment, regardless of the personal protective equipment (PPE) a person is wearing. There are two categories, per NFPA 70E, of "working on:" Diagnostic (testing) is taking readings or measurements of electrical equipment with approved test equipment that does not require making any physical change to the equipment; and Repair, which is any physical alteration of electrical equipment (such as making or tightening connections, removing or replacing components, etc.).

Working on, or near: Persons within the Restricted Approach Boundary of exposed energized electrical equipment.

Working space: Access and the working area around electric equipment to permit ready and safe operation and maintenance. See Table 3.

Contact Information

Robin McCall-Miller, Occupational Safety Program Manager