Operation and Maintenance - hdbk109220040171

DOE-HDBK-1092-2004

3. Consider magnetic forces in both normal-operation and short-circuit conditions. Use

conductors that have appropriate physical strength and are adequately braced and

supported to prevent hazardous movement.

4. Inductive circuits may create high-voltage hazards when interrupted. Careful circuit design

will include a method to bleed off power safely should an interruption occur.

10.8.2.3 OPERATION AND MAINTENANCE

Follow these guidelines for working on circuits operating at 50 V or less that are treated as

hazardous:

1. Work on such circuits when they are de-energized.

2. If it is essential to work on or near energized low-voltage, high-current circuits, observe the

safety rules as if the circuits were operating at more than 50 V. Refer to Section 2.1.2,

"Considerations for Working on Energized Systems and Equipment" and 2.13.4, "Safe

Energized Work (Hot Work)."

10.8.3 CONDITIONS OF HIGH VOLTAGE AND LOW CURRENT

10.8.3.1 HAZARDS

When the output current of high-voltage supplies is below 5 mA, the shock hazard to personnel

is low. Where combustible atmospheres or mixtures exists, the hazard of ignition from a spark

may exist. High-voltage supplies (ac or dc) can present the following hazards:

1. Faults, lightning, or switching transients can cause voltage surges in excess of the normal

ratings.

2. Internal component failure can cause excessive voltages on external metering circuits and

low-voltage auxiliary control circuits.

3. Overcurrent protective devices such as fuses and circuit breakers for conventional

applications may not adequately limit or interrupt the total inductive energy and fault currents

in highly inductive dc systems.

4. Stored energy in long cable runs can be an unexpected hazard. Safety instructions should

be in place to ensure proper discharge of this energy.

5. Secondary hazards such as startle or involuntary reactions from contact with high-voltage

low-current systems may result in a fall or entanglement with equipment.

10.8.3.2 DESIGN CONSIDERATIONS

Personnel in R&D labs may encounter energized parts in a variety of configurations, locations,

and under environmental conditions that are not usual for most electrical power personnel.

Sometimes the equipment can be designed to incorporate mitigation of the hazards associated

with working on such equipment. If not, then safe operating procedures must be developed and

used.

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