Specifications

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From the limited information provided in the two previous
examples, except for the maximum service current requirement,
it is not obvious whether a power panelboard or a switchboard
should be used at the service entrance. This determination is
usually made by the customer or a consulting engineer based
on the overall requirements of the application. The service
entrance and other application requirements are then detailed in
specifications communicated to potential suppliers in a request
for proposal (RFP).
Circuit Breakers Circuit breakers are used in panelboards and switchboards to
provide automatic circuit protection and a manual means of
energizing and de-energizing a circuit. Like the residential circuit
breakers previously discussed, most circuit breakers used in
commercial applications in the United States are molded case
circuit breakers (MCCBs) which conform to NEMA AB1 and UL
489 specifications.
The circuit breakers used in residential applications and many
of the circuit breakers used in commercial applications are
thermal-magnetic circuit breakers. Thermal-magnetic circuit
breakers are so named because they have a trip unit that
trips for an overload condition when it gets too hot and trips
immediately when it magnetically senses a short circuit.
Siemens offers a variety of molded case circuit breakers with
thermal-magnetic trip units and current ratings up to 2000
amps.
O
N
O
F
F
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O
100
100
Am
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Type/Tipo
NEG
Fra
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e-
EG
Molded Case Circuit Breakers with Thermal Magnetic Trip Units
In many commercial applications, it is necessary to coordinate
circuit breaker tripping so that the downstream circuit breaker
closest to a fault trips first, and breakers upstream only trip
when necessary. Proper coordination reduces the likelihood
of nuisance tripping or more extensive power outages than
necessary in response to a fault. Trip coordination requires
appropriate selection of circuit breakers and other circuit
protection devices. In addition, circuit breakers with adjustable
trip characteristics can be used.