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Technical Data
Effective: May 1998
Page
14
TD.44A.01.T.E
Cutler-Hammer
Magnum DS
Metal-Enclosed
Low-Voltage Switchgear
Group Motor Feeder Breakers
Typical loads for such circuits are
motor control centers. The feeder
breakers may be either manually or
electrically operated as preferred, and
are usually equipped with long and
short delay trip protection only for
coordination with the individual motor
circuit devices. The minimum long
delay pickup setting should be 115% of
the running current of the largest
motor in the group, plus the sum of the
running circuits of all other motors.
Motor Starting Feeder Breakers
These breakers are usually electrically
operated, with long delay and instanta-
neous tripping characteristics for
motor running, locked rotor and fault
protection. The breaker sensor rating
should be chosen so that the long
delay pickup can be set at 125% of
motor full load current for motors with
a 1.15 service factor, or at 115% for all
other motors. Contactors are recom-
mended for this application when there
are a number of daily operations
involved.
When system short circuits are less than
40 times the motor full load current, the
motor breaker tripping characteristic
should include a short delay characteris-
tic for greater fault protection.
Application
Feeder Breakers – General
Circuit breakers for feeder circuit pro-
tection may be manually or electrically
operated, with long and short delay or
long delay and instantaneous type trip
devices, and trip settings, as required
for the specific circuit and load require-
ments.
Feeder breakers as selected in Tables
A1 through A4 have adequate inter-
rupting ratings, and are assumed to
have adequate continuous current rat-
ings for maximum load demands.
General purpose feeder breakers, such
as for lighting circuits, are usually
equipped with long delay and instanta-
neous trip devices, with the long delay
pickup set for the maximum load
demand in the circuit. Where arcing
fault protection is required, the instan-
taneous trip setting should be as low
as practicable consistent with inrush
requirements.
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