Speedfax 2017

Low-voltage Switchgear
Type WL Low-voltage Metal-Enclosed Switchgear—WL CIrcuit Breakers
Selection
Selection Criteria for WL Circuit Breakers
SWITCHGEAR
14
The basic criteria for selecting circuit
breakers is:
Maximum Available Short Circuit
at the installation point. This value
determines the short circuit current
interrupting rating or short circuit
current withstand rating of the circuit
breaker.
Rated Current In which is to flow
through the respective circuit breaker
continuously. This value may not be
greater than the maximum rated current
of the circuit breaker. The rated current
for the WL is determined by the rating
plug, up to the maximum frame rating.
Ambient Temperature of the circuit
breaker.
Design of the circuit breaker.
Protective Functions of the circuit
breaker.These are determined by the
selection of the appropriate trip unit.
Dynamic Arc-Flash Sentry (Patent
Pending) A unique feature of the WL
trip unit allows the system designer to
achieve lower levels of arc flash energy
and delayed tripping for selective trip
coordination purposes.
Dynamic Arc-Flash Sentry (DAS)
employs the unique dual protective
setting capability of the 776 trip units,
coupled with the ability to easily toggle
to a lower arc flash parameter set. A
normal operation parameter set can be
optimized for selective trip coordination,
while the second set is optimized for
lower arc flash energy levels. The
dynamic action comes from the ability
to switch from the normal operation
set to the arc flash limiting set based
on the presence of personnel as they
approach the flash protection boundary.
A wide variety of switching methods
may used based on the needs of a
particular facility. The capabilities range
from fully automatic switching using
appropriate occupancy sensors to
manual switching via a key operation.
14-58
Siemens Industry, Inc. SPEEDFAX Product Catalog