Adjustments; Input Fuses - GE AF-600 FP User Manual

4. Adjustments

The AF 600 FP & Bypass panel has several user settable adjustments, which allow it to be tailored specifically
for your 3-phase induction motor. Setting these adjustments appropriately is an important factor in ensuring
that applicable safety codes are met and that your bypass panel, wiring, and motor are adequately protected.
The following list comprises all of the user adjustable devices/components inside the AF 600 FP & Bypass
panel. The user may wish to have a copy of NFPA 70-2008 (commonly known as the National Electric Code or
simply NEC) available for reference when setting these adjustments.

Input Fuses

DEH40602 – Page 12
Main input fuses are provided standard with your AF 600 FP & Bypass panel. In
general there are two configurations that utilize input fuses; 1) input disconnect
with load side separately mounted fuses and 2) input Fused Disconnect where
the fuses are an integral part of the disconnect. If your panel was ordered with
the circuit breaker option, the disconnect device and fuses are replaced by the
circuit breaker. The main input fuses provided with your bypass panel has been
closely coordinated to provide short circuit protection for the inverter along
with short circuit and over current protection for the motor. In "Drive" mode of
operation, the fuses only provide short circuit protection due to the fact that the
inverter has inherent over current protection. In "Bypass" mode of operation,
the fuses provide both short circuit and over current protection for the motor.
UL listed Class J time-delay fuses are provided with your panel. These fuses
have been sized in accordance to NEC section 450-52 and Table 450-152. NEC
states fuses of this type are to be sized at 175% of motor full-load amps (FLA).
Due to the fact that actual motor FLA along with starting current requirements
vary between manufacturer and motor types the fuses provided are based on
standard NEC motor data. Verify that actual motor FLA * 1.75 is equal to or
greater than the input fuse amp rating. In the case where the actual motor FLA
* 1.75 is less than the provided fuses amp rating then smaller fuses may need
to be installed to be in compliance with NEC section 430-52 and Table 430-152.
Please note exception 1 to NEC 430-52, which states that where the calculated
fuse amp rating does not correspond to a standard fuse size the next higher
standard fuse size may be used. In cases where the fuses provided is not
sufficient for the starting current requirements of the motor, please note
exception 2-b to NEC 430-52. Exception 2-b states the rating of a time-delay
fuse may be increased but shall not exceed 225% of the motor FLA in any case.
In the case where a larger or smaller fuse is required, a limiting factor in the
bypass panel may be the fuse holder. The appendices provide a table for the
maximum fuse size permitted in the existing fuse holder.
Coordinating the fuses for the bypass starter is the over current protection
coordination between the Class 20/30 overload relay and the fuse's over
current protection. This coordination is to avoid nuisance blowing of fuses.
Coordination between the inverter's short circuit rating and the fuse's rms let
through currents during a short circuit condition has also been closely
evaluated. Changing the main input fuses may impact one or both of the
above coordination issues. Therefore if it is necessary to change the input
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AN 11-2021 Rev 05, 12/15/2011