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Posted Apr 29 2015 | by admin in Circuit Breaker Info,Uncategorized with | No Comments
Sierra Circuit Breaker is a leader in supplying Square D SEF and SED insulated case breakers to the commercial and industrial markets.
We have a wealth of experience working with these breakers and can repair most models.
If you have an older vintage Sierra Circuit Breaker can help retrofil
existing switchgear with the newer Square D Micrologicâ„¢ Â Series trip
unit models. We have new surplus and reconditioned models in stock.
All our circuit breakers carry a full 1 year warranty. If you need
something in a hurry feel free to call us anytime 24hr/day we can get
you up and running same day in most cases.
General Information for techies:
Square D electronic trip insulated case circuit breakers are
equipped with the MICROLOGIC Full-function Trip System. This
trip system provides adjustable tripping functions and characteristics
using true root-mean-square (rms) current sensing.
MICROLOGIC trip systems use a set of current transformers
(called CTs or sensors) to sense current, a full-function trip unit
to evaluate the current, and a tripping solenoid to trip the circuit
breaker. Adjustable rotary switches on the trip unit allow the
user to set the proper overcurrent or ground current protection
required in the electrical system. If current exceeds a set value
for longer than its set time delay, the trip system opens the
circuit breaker.
Circuit breakers are shipped with the long-time pickup switch
set at 1.0 and all other trip unit adjustments set at their lowest
settings. Actual settings required for a specific application must
be determined by a qualified consultant or plant engineer. A
coordination study is recommended to provide coordination
between all circuit breakers in the distribution system.
RMS Sensing:
The sensing system on an electronic trip insulated case circuit
breaker responds to the flow of current through the circuit
breaker. Electronic trip circuit breakers are limited to ac systems
because the electronic trip system uses current transformers to
sense the current.
The MICROLOGIC trip system samples the current waveform
33 times per cycle on a 60 Hz system. It then uses this data to
calculate the true rms current through the 13th harmonic.
This true rms sensing gives accurate values for the magnitude
of a non-sinusoidal waveform. Therefore, the heating effects of
harmonically distorted waveforms are accurately evaluated.
Electronic trip circuit breakers with MICROLOGIC trip systems
can be used on 50/60 Hz systems with alternating current (ac)
to direct current (dc), dc to ac, and ac to ac converters. This
includes applications that use silicon-controlled rectifiers
(SCRs) and adjustable frequency controls.
Rating Plugs:
Rating plugs are used to determine the circuit breaker ampere
rating (P) according to the following equation:
The ampere rating and the long-time pickup switch are then
combined to determine the circuit breaker continuous current
rating. For example:
Rating plugs are available with multiplier values ranging from
0.40 to 1.00. If the rating plug is not installed, the circuit breaker
will operate safely, but the trip unit will default to a rating plug
multiplier of 0.40.
Rating plugs and ammeter/trip indicators are subject to damage
from static charge. Internal damage can result if these devices
are handled by their contacts. If either device is removed from
the trip unit, it must be held against grounded metal, such as the
metal circuit breaker enclosure, for at least two seconds before
reinstalling.
SED
SEF