Power Supplies

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.