Circuit Breaker Trip Level; Motor Overload Trip Level - GE AF-600 FP User Manual

Circuit Breaker Trip Level

Motor Overload Trip Level

DEH40602 – Page 13
fuses please consult your preferred fuse supplier and/or your local GE starter
distributor for Type 2 and overload relay coordination.
The optional circuit breaker in the AF 600 FP & Bypass panel is a solid state
Spectra RMS molded case circuit breaker from GE. The purpose of the circuit
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breaker is to provide short circuit protection and over current for the panel
components, field wiring and the motor. The breaker uses a solid state sensing
element which calculates the true RMS
resulting in a tripping action which is very fast. For this reason the NEC allows
the trip level to be set at 700% of the motor FLA to allow for the high locked
rotor current which the motor draws during across-the-line starts (see NEC
section 430-52 and Table 430-152 of the NEC). Because instantaneous trip
circuit breakers are so fast acting, the NEC actually allows trip level settings up
to 1300% of motor FLA if it can be shown to be required by engineering
evaluation. When a motor is started across the AC line it can draw a very large
peak current for the first half-cycle which can cause nuisance tripping in
instantaneous trip breakers set at 700%. GE Motors & Industrial Systems has
conducted analyses, which show that certain models can require this 1300%
trip level to avoid nuisance tripping on across-the-line starts. Generally the trip
level will need to be higher for premium efficiency motors than for standard
efficiency ones.
The rating plugs for the circuit breakers in the AF 600 FP & Bypass panels have
been chosen to allow trip level settings up to 13 times the current ratings of the
panel. If the trip level is set at 13 times the motor FLA and the circuit breaker
still trips it is probably due to the fact that your motor has very high efficiency
and therefore exhibits the highest inrush currents. Possible corrective actions
are:
1. Make sure there is not an actual short causing the trip.
2. Try starting several times. The inrush level is a function of the point on the
AC line when the breaker is applied. Try enough times and you'll probably
apply power at a favorable point.
3. Try another rating plug. Perhaps the tolerances on the one included with
your breaker are unfavorable.
4. Start the motor with the adjustable frequency drive and then switch over to
bypass mode once the motor is up to speed. This will not trip the breaker
because the drive "soft-starts" the motor by applying a very low voltage
and gradually ramping up.
5. For NEMA E motors (super premium efficiency) the NEC 1996 version will
allow a trip setting of 1700% of motor FLA.
The overload relay in your AF 600 FP & Bypass panel is the C-2000
or Class 30 fixed heater type from GE which is panel mounted. Class 30
overload relays are utilized for panels rated 60Hp and above at 208 VAC plus
150Hp and above at 460 VAC. The overload relay carries all motor current
whether it is running from the drive or across the AC line (bypass mode).
Whereas the panel circuit breaker or input fuses is intended to provide short
circuit protection for the panel components, field wiring and the motor, the
overload relay's function is to provide continuous long term overload protection
against loads which draw current in excess of the motor's rating.
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value of the current every cycle,
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AN 11-2021 Rev 05, 12/15/2011
Class 20
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