UFC 3-560-01
6 December 2006
Including change 1, 7 December 2006
9-4
ENERGY STORING PROTECTIVE DEVICES.
9-4.1
Electrical Charge.
WARNING
Protective devices such as surge arresters, choke coils, and capacitors
store electrical charges as a byproduct of their protective mechanism.
This stored charge must be discharged to ground before such devices can
be considered deenergized. Always wear appropriately rated personal
protective equipment, including eye/face protection when deenergizing or
energizing these devices., and use appropriate PPE in accordance with
Chapter 4 requirements.
9-4.2
Surge Arresters. A surge arrester limits overvoltages and bypasses the
related current surge to a ground system that absorbs most of the energy. An
overvoltage condition can be caused by a fault in the electrical system, a lightning
strike, or a surge voltage related to load switching. All surge arrester equipment must
be considered as loaded to full circuit potential, unless it is positively disconnected from
the circuit. Be sure the permanent ground conductor is intact before any work is
performed.
9-4.2.1 High-voltage substation and at-grade surge arresters must always be
provided with screens or fences to prevent possible contact while parts of the surge
arresters may be live. The screen or fence must have a gate large enough to permit the
removal of individual units. The gate must be provided with a lock and an authorized
person must keep the key.
9-4.2.2 Surge arresters must never be touched or approached, unless they are
completely disconnected from all live lines and live equipment, and all parts have been
discharged to ground and effectively grounded.
9-4.2.3 Horn gap switches must be fully opened and completely separated from all
live lines and equipment whenever it is necessary to work near a surge arrester.
9-4.2.4 If the first attempt to disconnect a surge arrester is unsuccessful, wait 2 or 3
minutes before making another attempt so not to cause an internal fault.
9-4.3
Choke Coils. Choke coils are inductors that operate in a manner similar to
surge arresters, except that they operate on over-frequency rather than over-voltage.
9-4.4
suitable container. Power capacitors are used to provide power factor correction.
Coupling capacitors are used for coupling communication circuits to metering circuits.
Because capacitors can hold their charge, they are not electrically deenergized
immediately after being disconnected from an energized line. Capacitors on electric
9-6
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