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GEH-1788
Type IAC Time Overcurrent Relay
Aid in making the proper selection of relay
settings may be obtained on application to the near-
est Sales Office of the General Electric Company.
INSTANTANEOUS UNIT
Select the current above which is desired to
have the instantaneous unit operate and set the
adjustable pole piece so that the top of its hexagon
head is even with the desired calibration on the
scale.
To raise or lower the pole piece, loosen the
locknut and turn it up or down and then tighten in
pOSition.
The contacts should be adjusted to make at
about the same time and to have approximately
1/8 inch wipe.
This adjustment can be made by
loosening the screws holding the stationary contacts
and moving the contacts up or down as required.
,A-C TRIPPING UNIT
The a-c tripping unit should not require any
attention other than occasional cleaning of the con-
tacts.
However,
if
the adjustment should be lost,
it may be restored as follows:
CONTACT ADJUSTMENT
With the unit de-energized, the movable contact
should lie against the stationary contact with enough
tension to always insure a good closed circuit. The
movable contact brush should be free of any kinks.
Also this contact brush should not touch the com-
pound bushing supported from the top of the arma-
ture.
The brass backing strip should be adjusted
to allow a 1/16-inch contact gap with the contacts
open.
The compound bushing support should be
adjusted to allow the back of the movable contact
to just touch the brass backing strip when the
armature operates to open the contacts. The outer
edge of the compound bushing should be approximate-
ly 1/32 inch from the inner edge of the stationary-
contact supporting post.
ARMA TURE ADJUSTMENT
Loosen the two screws which hold the armature-
assembly bracket to the bottom of the frame. Slide
the bracket in or out, whichever is necessary, until
the armature just touches the pole face of the upper
core.
In this position, the armature should be
about 1/32 inch from the pole face of the lower
core.
Next, slide the bracket in until the armature
leaf spring assumes a vertical position and is
TO TIMER
"STOP"
6
-
-~
TO
:NDICATI~~
LIGHT
'I""E~
CY[CKIV:;
PlryUp
,JF
~AA!N ~'N
iT
- - - -
--~
TO INCICATING LIGHT
liYE~
CHECKING PICKUP OF
INSTANTANEO~S
UNIT
,
6
0
2
.3
4
o
0
0
0
7
8
9
lC
-
---
XLA:.3 TEST PLuG
VARIABLE RESISTOR
TO TiMER
"START"
TO ACCURATELY REPRODUCE
RELAY CHARACTERISTICS
ALL TESTS SHOULD BE
MADE WITH RELAY I N CASE.
IJ
IN. RECOMMENDED VOLTS.
120 AT RATED FREQUENCY
Fig.19 Test Connections for Testing Pickup
&
Time Curve
of lAC Relays
spaced clear of both armature and the vertical tip
of the bracket. With this setting, the armature should
be flush against the pole face of both cores, and
should put enough pressure on the armature to
always return it flush against the pole face of the
lower core after each operation of the unit. This
alignment is important as a slight gap between
armature and pole face of the lower core after the
unit operates may cause contacts to open momen-
tarily, dropping the relay target when the circuit
breaker is reclosed.
Under these conditions, the
momentary opening of the contacts is due to the
shock of the armature being pulled in against the
pole face when the lower coil is energized. Ex-
cessive pressure on the armature, caused by the
bracket being pushed in too far, will result in too
high a pickup or chattering of the movable contact
during operation of the unit.
Tighten the bracket
screws securely after the proper adjustment has
been obtained.
OPERATION
The pick-up current should be checked on one
or more of the taps and the time should be checked
for one or more dial settings.
Recommended test connections for the
abov~
test are shown in Fig. 19.
14
Before the relay is put into service it should be
given a check to determine that factory adjust-
ments have not been disturbed.
The time dial
will be set at zero before the relay leaves the
factory.
It
is necessary to change this setting in
order to open the relay contacts.
...,
~.
. .
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