Quantcast Circuit Breakers

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(b) Disconnect switches should be closed with a quick positive motion, with sufficient
force to ensure full contact with the clips. Excessive force should not be exerted in the
movement, as such force may break the insulators. If a disconnect switch is accidentally closed
when the associated circuit breaker or other circuit interrupting device is closed, do not attempt
to reopen the disconnect switch. Leave it closed, get away from it at once, and open the circuit
by means of the circuit breaker or other suitable circuit interrupting device.
(c) A disconnect switch should be opened slowly so that it can be reclosed quickly, if
necessary. If an operator should start to open a disconnect switch and finds that an arc of unusual
severity is formed, this indicates that the circuit breaker or other circuit interrupting device is
closed or that there is trouble on the circuit or equipment controlled by the disconnect switch.
The operator should immediately reclose the disconnect switch, leave it closed, and open the
circuit by means of a circuit breaker or other suitable circuit interrupting device before
attempting to open the disconnect switch again.
(d) After operating a switch, check to see that it is fully closed and latched or fully
open as intended.
(e) Do not use undue force in attempting to operate a switch. The operating
mechanism is carefully designed for the switch. Any undue force applied by an extension of the
operating handle, or an extra person on the operating handle or switch stick, may cause severe
damage to the switch or mechanism.
(f) Power-operated switches should be operated periodically to assure that the switches,
their mechanism, and control features are functioning properly. Where the circuit conditions will
not permit operating the switch energized, and the circuit cannot be deenergized for this purpose,
it is suggested that arrangements be made to disengage the operating mechanism to be checked
(provided that this method does not adversely affect the overall adjustment).
3.5 CIRCUIT BREAKERS. A circuit breaker is a mechanical device for closing and
interrupting a circuit and carrying current under both normal load and fault current conditions.
3.5.1 Purpose. One function of circuit breakers is to prevent or limit damage to circuits and
apparatus during fault or overload conditions and to minimize their effect on the remainder of the
system. During a fault or overload, the zone that includes the faulted or overloaded apparatus is
isolated from the system. A circuit breaker is also used for circuit switching under normal
conditions. A circuit breaker, when operated within its rating, is capable of closing into, of
carrying, and of interrupting short-circuit current without being damaged. A circuit breaker
maintains open-circuit conditions with operating voltage across its terminals.
3.5.2 Classes. There are generally two classes of circuit breakers.
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