is unsuccessful, wait 2 or 3 minutes before making a further attempt so as not to cause an
6.7.2 Choke Coils. Choke coils are inductors that operate in a manner similar
to surge arresters, except that they operate on overfrequency rather than overvoltage.
6.7.3 Capacitors. Capacitors consist of electrical condensers housed in suitable
containers. Power capacitors provide for power factor correction. Coupling capacitors
are used for coupling communication circuits to metering circuits. Because capacitors can
hold their charge, they are not electrically dead immediately after being disconnected from
an energized line. Capacitors on electric lines should be provided with discharge devices
for draining the electrical charge to 50 volts or less in 5 minutes, after the capacitors have
been completely disconnected from the circuit.
126.96.36.199 Capacitor Discharge Circuits. The operation of these discharge units
should not be depended upon for safety, since they may be burned out or otherwise not
functioning as designed. Line capacitors removed from service for any purpose should be
considered at full voltage or higher, until the terminals have been short circuited and
discharged to ground by an approved method. Do not short circuit terminals until
capacitors have been de-energized for at least 5 minutes.
a. It is not safe to use fuses or disconnect switches to disconnect large capacitor
banks of 60 kilovolt-reactive single-phase, 180 kilovolt-reactive three-phase, and larger.
Circuit breakers should be used.
b. After disconnecting all capacitor banks, wait 5 minutes. Short-circuit and
ground all terminals. All operations should be performed using rubber gloves or a hot
stick or both. On wye-connected banks, the neutral may or may not be floating. In either
case, it should be grounded.
c. Safe practice requires that the ground and short-circuit placed on capacitors be
left on until work has been completed. When working on or testing capacitors in the
shop, the work area should be barricaded as a safety measure for other workers.
188.8.131.52 Coupling Capacitors: A little known characteristic of coupling
capacitors makes them especially hazardous to personnel if not properly grounded. This
characteristic is their extremely high resistance, which results in a long discharge period.
During shipping or storage a coupling capacitor should always have a shorting wire.
During maintenance, a grounding wire should be connected to each exposed metal
terminal that anyone can contact. Grounding wires should be left in place for the entire
duration of maintenance to ensure discharge.
Instrument Transformer Safety. Instrument transformers
primary circuit voltage or current in a low-voltage secondary circuit for use in metering or
relaying the primary circuit.