Electrical Test Instruments PI-2500-G2 and PI-5000-G2
Section V - Service Information and Documentation
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Copyright(C) 1994-2021 Electrical Test Instruments, LLC. All Rights Reserved
Page IV-17
MOTOR OVERLOAD RELAYS
The motor overload relay is designed to provide overload protection for a mo-
tor; therefore, it offers only one time/current characteristic, which is essentially
a long-time delay. It may be multi-pole; however, most relays are single pole. In
the case of a multi-pole device each pole is tested individually as in the case of
a multi-pole direct acting circuit breaker.
The motor overload relay contains two separate circuits. The current carrying
circuit which contains the relay's operating coil or heater. The control circuit
which contains a set of contacts; these contacts open when the relay "oper-
ates". It is the opening of these control circuit contacts that deenergizes the
motor starter holding coils, thus allowing the starter contactors to open, shut-
ting down the motor.
Timing Tests
1.
Consult the relay manufacturer's literature to determine any necessary
precautions and the expected timing test results. The test current should
be 3 to 4 times the rating of the relay operating coil or heater.
2.
Follow steps 1 through 16 in pre-test installation and setup, as required, to
set up the breaker test set.
3.
Setup MAC-21 for C.L. Maint (MAINTAIN on).
4.
Set MAC-21 RANGE to lowest range that is greater than desired test cur-
rent.
5.
Set TIMEBASE to CYCLES.
6.
Press PRESET key. Adjust preset time to 5.0 cycles. This value may be set
higher or lower, depending on trip characteristics of breaker.
7.
Press PRESET again to return to normal mode.
8.
Select MEMORY mode.
9.
Connect the relay operating coil or heater circuit terminals to the breaker
test set common terminal and the proper output tap terminal.
10.
Connect the relay control circuit contacts to the CONTACTS terminals and
determine that they are closed by observing the CONTINUITY lamp.
11.
Repeatedly jog the INITIATE button, while adjusting the OUTPUT
CONTROL higher, until the desired test current is read on the ammeter. If
insufficient current is obtained at maximum position of the Vernier, set the
OUTPUT TAP control to the next higher tap, return the Vernier to zero, and
continue.
