Electrical Test lnstruments MAC-20 Retrofit
Package
Section lll -
Operating
lnstructions
MOTOR
OVERLOAD RELAYS
.
The
motor overload
relay
is designed to
provide
overload
protection
for a motor;
therefore, it offers only one time/current
characteristic,
which is essentially a long
time
delay. lt 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
"operates".
lt is the opening of
these control circuit
contacts that deenergizes the motor starter holding coils, thus
allowing the starter contactors to open,
shutting 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 18 in
general
test
procedures,
as required, to set up the
breaker test set.
3. Setup
MAC-20 for
C.L.
MOM.
'..
4. Set MAC-20 RANGE to lowest range that is
greater
than desired test current.
5. Set
TIMEBASE
to CYCLES.
6.
Press
PRESET
key. Adjust
preset
time
to
6.0 cycles.
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. Conneci
the relay control circuit contacts to the CONTACTS
binding
posts,
and
determine that they
are closed by observing the CONTINUITY
lamp.
1
1. Repeatedly
jog
the INITIATE button,
while adjusting the OUTPUT CONTROL
higher, until
the
desired test current
is read
on
the ammeter. lf insuffrcient 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.
12. Press
RESET button.
13. Set MAC-20 to
N.C. mode. Set LATCH on.
14. Press and
release INITIATE button; CLOSE
or OUTPUT ON
light should
glow,
timer should operate,
and current should
indicate on display.
.'
15. When the
relay control circuit
contacts open, the test set output
should deenergize
Electrical
Test lnstruments, lnc.
Page lll-14
Copyrisht(C)
1
994-1998
All Rights Reserved
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