GE IAC53A User manual

INSTRUCTIONS
GEH-1788L
TIME OVERCURRENT RELAYS
TYPES
IAC53A IAC53R
IAC53B IAC54A
IAC53C IAC54B
GENERALf) ELECTRIC

GEH-1788 Tvne IAC Time Overcurrent Relay
TOP PIVOT
TAP PLUG
TAP BLOCK
SEAL-IN
UNIT
HOLDING
--- TIME DltlL
COIL
SEAL-IN
DISK SHAFT
TARGET
MAIN
SEAL-IN ._-- MOVING
UNIT CONTACT
STATIONARY
CONTACT, MA:N
LEFT
STATIONARY
BRUSH
AND
SEAL-I N--
CONTACT
UNIT
ASSEMBLY
STATIONARY
CONTACT, MAGNET
RIGHT DISK
SEAL-IN
MOVING
CONTACT
ASSEMBLY
Fig. I
The Induction Unit for Type lAC Relays (Front View)
DISK
AND
SHAFT---
LOWER .'
JEWEL SCREwj
COIL
ANO
TAP
BLOCK
-
ASSEMBLY
Fig. 2 The Induction Unit for Type lAC Relays (Rear View)
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TIME OVERCURRENT RELAYS
TYPE lAC
INTRODUCTION
Type
Contact Instan. A-C Trip
Induc. Outline
lnt.
Circuits Unit
IAC53A(-)A
One No
IAC53B(-~A
One Yes
IAr.53C(- A One No
JAC53R(-)A
One Yes
IAC54A~-~A
Two No
IAC54B - A
Two Yes
The Types IAC53 and IAC54 relays are time
overcurrent relays with a very-inverse time char-
acteristic. They are employed to protect against
overcurrent on single-phase and poly-phase circuits.
The various relays described in this instruction book
differ in the number of circuits they close, and if an
instantaneous unit and/or an a-c tripping unit is
included.
These relays consist of an induction unit or an
induction unit with an instantaneous unit which per-
Unit Unit
&P. D.
Conn.
No
One
Fig. 20
Fig. 12
No
One
Fig. 20
Fig. 13
Yes On~
Fie:. 20
Fig. 14
Yes
One
Fig. 20
Fig. 15
No
One Fig. 20
Fig. 16
No
One
'Fig. 20
Fig. 17
.-
mits instantaneous tripping for exteremely high cur-
rents, or an induction unit with an a-c tripping unit for
use where d-c power is unavailable or a-c tripping is
preferred. Since practically all Type IAC relays are
composed of various combinations of the above (that
is, the induction unit, the instantaneous unit and the
a -c tripping unit), they are, for convenience, describ-
ed separately in the following text. The above table
indicates the units comprising each type and also lists
the internal connections and outline and panel drilling
diagrams.
INDUCTION UNIT
INTRODUCTION APPLICATION
The induction unit is the basic unit in all Type
JAC relays. Figs. 1 and 2 show the induction unit
mounted in the cradle. These units are of the induc-
tion-disk construction type. The disk is actuated by a
current operating coil on a laminated U-magnet. The
disk shaft carries the moving contact which completes
the alarm or trip circuit when it touches the station-
ary contact or contacts. The disk shaft is restrained
by a spiral spring to give the proper contact-closing
current and its motion is retarded by a permanent
magnet acting on the disk to give the correct time
delay.
There is a seal-in unit mounted on the front to
the left of the shaft. This unit has its coil in series
and its contacts in parallel with the main contacts
such that when the main contacts -close the seal-in
unit picks up and seals in. When the seal-in unit
picks up, it raises a target into view which latches
up and remains exposed until released by pressing
a button beneath the lower left corner of the cover.
The induction unit is the main unit in all Type
JAC relays, supplying the very inverse time delay
characteristics of the relay and sounding an alarm or
tripping the breakers for overload currents which
cause it to close its contacts.
OPERATING CHARACTERISTICS
The induction unit may have one or two circuit-
closing contacts which close as the current increases
to the pick-up value as set on the tap block. The
time delay in closing the contacts is determined by
the setting of the time dial (Fig. 1). The time-cur-
rent characteristics are shown in Fig. 3.
RATINGS
The induction unit is designed to use anyone of
four operating coilS, each having a different com-
bination of taps as follows, 4,5,6,7,8,10,12, and 16
amperes; 1.5,2.0, 2.5, 3.0, 4.0, 5.0 and 6.0 amperes;
0.5, 0.6, 0.8, 1.0, 1.2, 1.5 and 2.0 amperes; 0.1,
0.12, 0.16,
0.2, 0.24, 0.3 and 0.4 amperes.
These instructions do not purport to cover all details or variations in equipment nor to provide for
,}very possible contingency to be met in connection with installation, operation or maintenance. Should
further information be desired or should particular problems arise which are not covered sufficiently for
the purchaser's purposes, the matter should be referred to the General Electric Company.
To the extent required the products described herein meet applicable ANSI, IEEE and NEMA standards;
but no such assurance is gi ven wi th respect to local codes and ordinances bec~use they vary greatly.
3

GEH-1788 Type IAC Time Overcurrent Relay
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MULTIPLES OF RELAY TAP SETTING
Figure 3 <088880270 [3]) Time-Current Curves for Type IAC Relays with
Very-Inverse-Time Characteristics
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CALI BRATION
PLATE
ADJUSTABLE
POLE PIECE
INSTANTANEOUS
UNIT
OPERATING
COIL
TARGET
STATIONARY
CONTACTS
MOVING
CONTACT
ASSEMBLY
Fi g. L+
Type lAC Relay with an Instantaneous Unit
(Front View)
The current-closing rating of the contacts is
30 amperes for voltages not exceeding 250 volts.
The current-carrying ratings are affected by the
selection of the tap on the target and seal-in coil
as indicated in the following table:
Function
Amperes, a-c or d-c
2-Amp Tap
0.2 Amp Tap
Tripping Duty 30 5
Carry Continuously
3 0.3
Operating Range
2-30
0.2-2
Resistance
0.13
7
Impedance at 60 cy 0.53 52
If the tripping current exceeds 30 amperes an
auxiliary relay should be used, the connections being
such that the tripping current does not pass through
the contacts or the target and seal-in coils of the
protective relay.
Type lAC Time Overcurrent Relay GEH-1788
SHORTING
COIL
MAIN
COIL
A-C
TRIPPING
UNIT
Fi g. S Type lAC Relay with an A-C Trip Unit
(Rear View)
BURDENS
Burdens for the standard coils are given in the
following table. These are calculated burdens at
five amperes based on burden of minimum tap.
Volt-ampere burdens for the lowest tap on any
of the three coils can be determined for any value
of current, up to 20 times tap setting, from Fig. 6.
Coil
Freq.
Tap Amps
Volt
Imp.
PF
Amps Amps
Ohms
4-16
60 4 5
2.0
0.08 0.50
50
4 5 1.7
0.07 0.50
25 4 5 1.3
0.05
0.61
1.5-6
60
1.5 5
14.5
0.58
0.42
50
1.5 5
12.0
0.48
0.42
25
1.5 5
9.0
0.36 0.55
0.5-2
60 0.5 5
105.0
4.20
0.35
50 0.5 5
86.0
3.45
0.34
25 0.5 5
82.0
3.28
0.55
* 3050
122
0.38
0.1-0.4
60
0.1
5
50 0.1 5
2546
102
0.36
------.
INSTANTANEOUS
INTRODUCTION
UNIT
The instantaneous unit is a small instantaneous
hinge-type unit which may be mounted on the right
front side of the induction unit (See Fig. 4). Its
contacts are normally connected in parallel with
the contacts of the main unit. Its coil is connected
in series with the operating coil of the main unit.
When the current reaches a predeterm:ned
value, the instantaneous unit operates, closing the
contact circuit and raising its target into view.
The target latches in the exposed position until
released by preSSing the button beneath the lower
left-hand corner of the relay cover.
5

GE8-1788 Type lAC Time Overcurrent Relay
26
24
22
20
18
16
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601'\.1
50"",
25"V
TAP
RANGE
0.5-2.0
AMPS.
601'\.1 TAP
RANGE
50"", 1. 5-6.0
A~PS •.
25"", TAP
60"" J RANGE
501'\.1 4-16
251'V AMPS.
o 2 4 6 8 10 12 14
16 18
20
MULTIPLES OF MINIMUM PICK-UP CURRENT
SATURATION CURVES FOR lO~EST TAPS OF
INOUCTION UNITS ON VERY INVERSE
TYPE lAC RELAYS
Fig. 6 Saturation Curves for Lowest Taps of tne Induction Unit of Type lAC Relays with
Very-Inverse-Time Characteristics
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1'ype lAC Time Overcurrent Relay U~H-17aa
0.030
0.025
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en 0.020
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u 0.010
CL
0.005
o o 1 2 4
OPERATI NG TIME
RANGE FOR ~y
PICKUP SETIING
5 6 7
MULTIPLES Of PICK-UP
9
10
Fig. 7A (K-6306872 [5]) Time-Current Characteristics for Original Instantaneous Unit
.025 t---+----+-+_
".oro +---+---4
.oos +--+----!-+'__..
1.5 2 B 9
10
~ULTI PLES OF PICKUP
Fig. 7B (0208A869 5-1) Time-Current Characteristics for the "Hi-Gil Unit
7

GEH-1788 Type IAC Time Overcurrent Relay
APPLICATION
The instantaneous unit is used on certain Type
IAC relay models to provide instantaneous tripping
for current exceeding a predetermined value.
OPERATING CHARACTERISTICS
* The instantaneous unit operates over a four-
to-one range and has its calibration stamped on
a scale mounted beside the adjustable pole piece.
Time-current characteristics are shown in Fig.
7A for the instantaneous unit used before 1977.
In 1977 the instantaneous unit was modified to
make it have a higher seismic rating. The new
instantaneous unit can be identified by the mark-
ing "Hi -G" moulded into the front mouldi ng jus t
above the target windows. The time-current
characteristic for the "Hi-G" unit is shown in
Fig. 7B.
RATINGS
The instantaneous unit is designed to use
the coils listed below;
Coil Freq Amp
Volt-
Imp.
P.F.
Amp
Ohms
0.5-2
60 5 360 14.4 0.74
1-4 60 5 90
3.6
0.77
2-8
60 5 22.5
0.90 0.83
25 5
8.0
0.32 0.83
4-16
60
5 5.63 0.225
0.87
50 5
4.77
0.191 0.87
40 5 3.93 0.157
0.88
25 5
2.37
0.095 0.88
7-28
60 5 1.68 0.067
0.88
10-40
60 5 0.83 0.033
0.95
50 5
0.80 0.032 0.95
25 5 0.68
0.027
0.98
20-80
60 5
0.20
0.008 0.95
50 5 0.20 0.008
0.95
25 5 0.18
0.007
0.98
A-C TRIPPING UNIT
INTRODUCTION
The a-c tripping unit is a Type REA relay unit
designed to energize a circuit-breaker trip coil
from its associated cuz:rent transformer upon the
operation of the main unit of the Type IAC relay. It
transfers the current from the secondary of the
current transformer into the trip coil and removes
the current from the trip coil when the breaker trips.
The tripping unit is mounted on the rear of the
frame opposite the tapped operating coil of the in-
duction unit (see Fig. 5). The operation of this unit
is illustrated in Fig. 11. The secondary current
8 * Indicates revision
circulates through the induction unit current coil and
the main coil of the Type REA auxiliary tripping unit,
returning through the Type REA contacts to the cur-
rent transformer. Normally, most ofthefluxgener-
ated by the main Type REA coil passes through the
upper limb of the magnetic structure and holds the
armature firmly against this limb. When the contacts
of the induction unit close, the shorting coil of the
Type REA unit is short-circuited and current flows
in this coil by transformer action, causing a redis-
tribution of flux which actuates the armature and the
Type REA contacts. The opening of the Type REA
contacts causes the secondary current to flow through
the trip coil which trips the breaker.

A-C 8~ S
TRIP BLS
(-) --.------
2
3
5 5
51-3
.a=.!
6 6
5
.llii.
H
6
-------
Figure B (K-6375667 [2]) External Connections of
Three Type IAC53A Relays Used for Phase-to-
Phase and Ground Overcurrent Protection of a
3-Phase Circuit
A-C BUS
Figure 9. (K6375668-1) External Connections of
Three Type IAC53A Relays used in Conjunction
with Tripping Reactors for Protection of a 3-Phase
Circuit
Type IAC Time Overcurrent Relay GEH-1788
Device Function Numbers for Use with ALL
51-1 External Diagrams
50
51
51N
52
SI
TC
A
Instantaneous Unit
Overcurrent Relay, Type IAC
Ground Overcurrent Relay, Type IAC
Power Circuit Breaker
Seal-in Unit, with Target
Trip Coil
Auxiliary Contact, closed
when breake .. • closes
A-C IIJS
~
IOC
Figure 10. (K-6375669-6) External Connections of
Three Type IAC53R Relays Used For 3-Phase
Circuit Protection
9

GEH-l'/MM 'rype IAC 'rime Overcurrent Relay
APPLICATION
The a-c tripping unit is used in Type IAC relays
where a reliable direct-current tripping source is
not available and it is necessary to trip the breaker
from the current-transformer secondary.
RATINGS
T6S1 BREAKER
TRIP COIL
The a-c tripping Wlit has a continuous rating of CURRENT
five amperes but will operate on a minimum current TRANS
of 3.5 amperes. It should be used with three-
ampere trip coils. The contacts of these units will
transfer current-transformer secondary current up
to 100 amperes. For applications where the sec-
ondary current exceeds 100 amperes, the Type
REAllB relay, which has contacts rated 200 am-
peres, can be used in conjWlction with Type IAC
overcurrent relays. The Type REAllB is not
mOWlted inside the Type IAC case.
aURDENS
Burdens of the Type REA unit are given in the
following table:
Impedance
PF
Volt-
Frequency Amps in Ohms
Amperes
60 5 0.49 0.80
12.2
50 5 0.33
0.80
8.3
25 5 0.23 0.62 5.8 *
Fig. II Diagram Illustrating Operation of Type
lAC Relays having an A-C Tripping Unit
RECEIVING, HANDLING AND STORAGE
These relays, when not included as a part of a
control panel will be shipped in cartons designed to
protect them against damage. Immediately upon
receipt of a relay, examine it for any damage
sustained in transit. If injury or damage resulting
from rough handling is evident, file a damage claim
at once with the transportation company and promptly
notify the nearest General Electric Apparatus Sales
Office.
Reasonable care should be exercised in Wlpack-
ing the relay in order that none of the parts are
injured or the adjustments disturbed.
If the relays are not to be installed immed-
iately, they should be stored in their original car-
tons in a place that is free from moisture, dust
and metallic chips. Foreign matter collected on
the outside of the case may find its way inside
when the cover is removed and cause trouble in
the operation of the relay.
INSTALLATION
LOCATION
The location should be clean and dry, free from
dust and excessive vibration, and well lighted to
facilitate inspection and testing.
MOUNTING
* The relay should be mounted on a vertical
surface. The outline and panel diagram is shown
in Fig. 20.
CONNECTIONS
The internal connection diagrams for the various
10 * Indicates Revision
relay types are shown in Figs. 12 to 17 inclusive.
Typical wiring diagrams are given in Figs. 8 to
10 inclusive.
One of the mounting studs or screws should be
permanently grounded by a conductor not less than
No. 12 B & S gage copper wire or its equivalent.
INSPECTION
At the time of installation, the relay should
be inspected fur tarnished contacts, loose screws,
or other imperfections. If any trouble is fOWld,
it should be corrected in the manner described
under MAINTENANCE.

SEAL-IN LI '" I
i:i
INDUCTION
,...-·UNIT
UN:T· ~
1 1
2 6
O=SHORT FINGER
Fig. 12
Internal Connect ions for Type IAC53A
Relay (Front View)
I NDUClt
UNIT
Type IAC Time Overcurrent Relay GEH-1788
INOUCTION
UN I T I NSTAN.
UNIT
\ --
[.]
2 6
° SHORT FINGER
Fig. 13 Internal Connections for Type IAC538
Re lay (F ront View)
I~DUCTION
UNIT
SEAL-IN
A-C TRI
UNIT
UNIT
lNDUCTION
UNIT
l Ib
r1
1
:3
2 6
Fig. I ~ (K-6209660-7) Interna1 Connecti ons For
Type IAC53C Relay (Front View)
* Indicates Hevi"ion
I
NU
S N
T I
A T
N
=-_--t-r 1 NSTANT
UN.1 T
T
~ I ~ I [-1 ~ I ~ I
2 4 6 8 10
* Fig. 15 Internal Connections for Type IAC53R
Relay (Front View)
11

GEH -1 'I tits 'rype lAC 'rime ()vercurrent ttela.y
SEAL-IN
lI~, I T
Fi g. 16
CAUTION:
INDUCTION
SI
[.
1
3
I 1 6
• = SHORT FINGER
Internal'Connections for Type IAC5~A
r
2
Fi g. 17
v
IND~CTION
UNIT
6
INSTANT.
n:IT
INSTANT.
UI, IT
I 1
r
9 r
10
SHORT FINGER
Internal Connections for Type IAC54B
Every circuit in the drawout case has an
auxiliary brush. It is especially important on
current circuits and other circuits with shorting
bars that the auxiliary brush be bent high enough
to engage the connecting plug or test plug before
the main brushes do. This will prevent CT sec-
ondary circuits from being opened.
12
CONNECTING PLUG MAIN BRUSH CONNECTING BLOCK
\
NOTE AFTER ENGtlGING AUXILIARY BRUSH, CONNECTING PLUG
TRAVELS 1/4 INCH BEFORE ENGAGING THE MAIN BRUSH ON
THE TERMINAL BLOCK
Fig. 18 Cutaway of Drawout Case Showing Position of Auxil iary Brush
..-
0\
00

Type IAC Time Overcurrent Relay GEH-1788
ADJUSTMENTS
TARGET AND SEAL-IN UNIT
For trip coils operating on currents ranging
from 0.2 to 2.0 amperes at the minimum control
voltage, set the target and seal-in tap screw in
the 0.2-ampere tap.
For trip coils operating on cUfrents ranging
from 2 to 30 amperes at the minimum control
voltage place the tap screw in the 2-ampere tap.
The tap screw is the screw holding the right-
hand stationary contact of the seal-in unit. To
change the tap setting, first remove the connecting
plug. Then, take a screw from the left-hand
stationary contact and place it in the desired tap.
Next, remove the screw from the other tap and
place it in the left-hand contact. This procedure is
necessary to prevent the right-hand stationary
contact from getting out of adjustment. Screws
should not be in both taps at the same time.
INDUCTION UNIT
CURRENT SETTING
The current at which the contacts operate may
be changed by changing the position of the tap plug
in the tap block at the top of the relay. Screw the
tap plug firmly into the tap marked for the desired
current (below which the unit is not to operate).
When changing the current setting of the unit,
remove the connecting plug to short-circuit the
current-transformer secondary circuit. Next,
screw the tap plug into tap marked for the desired
current and then replace the connecting plug.
The pickup of the unit for any current tap is
adjusted by means of a spring-adjusting ring. The
ring may be turned by inserting a tool in the notches
around the edge. By turning the ring, the operating
current of the unit may be brought into agreement
with the tap setting employed, if for some reason,
this adjustment has been disturbed. This adjustment
also permits any desired setting intermediate be-
tween the various tap settings to be obtained. The
unit is adjusted at the factory to close its contacts
from any time-dial position at a minimum current
wi~hin five per cent of the tap plug setting. The
umt resets at 90 per cent of the minimum closing
value.
TIME SETTING
The setting of the time dial determines the
length of time the unit requires to close its con-
tacts when the current reaches the predetermined
value. The contacts are just closed when the dial
is set on O. When the dial is set on 10, the disk
must travel the maximum amount to close the
contacts and therefore this setting gives the max-
imum time setting.
The primary adjustment for the time of oper-
ation of the unit is made by means of the time
dial. However, further adjustment is obtained by
moving
the permanent magnet along its supporting
shelf; moving the magnet toward the main shaft of
the unit decreases the time, while moving it away
increases the time.
If selective action of two or more relays is
required, determine the maximum possible short-
circuit current of the line and then choose a time
value for each relay that differs sufficiently to
insure the proper sequence in the operation of the
several circuit breakers. Allowance must be
made for the time involved in opening each breaker
after the relay contacts close. For this reason,
unless the circuit time of operation is known with
accuracy, there should be a dfifference of about 0.5
second (at the maximum current) between relays
whose operation is to be selective.
EXAMPLE OF SETTING
The time and current settings of the over-
current unit can be made easily and quickly. Each
time value shown in Fig. 3 indicates the time
required for the contacts to close with a particular
time-dial setting when the current is a prescribed
number of times the current-tap setting. In order
to secure any of the particular time-current settings
shown in Fig. 3, insert the removable plug in the
proper tap receptacle and adjust the time-dial to
the proper position. The following example il-
lustrates the procedure in making a relay setting:
Assume a Type IAC relay is used in a circuit
where the circuit breaker should trip on a sustained
current of approximately 450 amperes; also, the
breaker should trip in 1.0 second on a short-circuit
current of 3750 amperes. Assume further that
current transformers of 60/1 ratio are used.
The current tap setting is found by dividing the
minimum primary tripping current by the current
transformer ratio. In this case, 450 divided by 60
equals 7.5 amperes. Since there is no 7.5 ampere
tap, the 8-ampere tap is used. To find the proper
time-dial setting to give 1.0-second time delay at
3750 amperes, djvide 3750 by the transformer
ratio. This gives 62.5 amperes secondary current
which is 7.8 times the 8-ampere ~etting. By re-
ferring to the time current curves'- (Fig. 3), it
will be seen that 7.8 times the minimum operating
current gives 1.0-second time delay when the relay
is set on the No.6 time-dial setting.
The above results should be checked by means
of an accurate timing device. Slight readjustment
of the dial can be made until the desired time is
obtained.
13

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.
ARMATURE 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 IN 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.
...,
~.
..

Type IAC Time Overcurrent Relay GEH-1788
MAINTENANCE
DISK AND BEARIN~S
The lower jewel may be tested for cracks by
exploring its surface with the point of a fine needle.
The jewel should be turned up until the disk is
centered in the air gaps, after which it should be
locked in this position by the set screw provided
for this purpose.
CONTACT CLEANING
For cleaning fine silver contacts, a flexible
burnishing tool should be used. This consists of a
flexible strip of metal with an etched roughened
surface, resembling in effect a superfine file. The
polishing action is so delicate that no sc;ratches are
left, yet corroded material will be removed rapidly
and thoroughly. The flexibility of the tool insures
the cleaning of the actual points of contact.
Fine silver contacts should not be cleaned with
knives, files, or abrasive paper or cloth. Knives or
files may leave scratches which increase arcing and
deterioration of the contacts. Abrasive paper or cloth
may leave minute particles of insulating abrasive
material in the contacts and thus prevent closing.
The burnishing tool described is included in the
standard relay tool kit obtainable from the factory.
PERIODIC TESTING
It is recommended that pickup of all units be
checked at least once every six months.
ACCEPTANCE TESTS
ELECTRICAL
A. MAIN UNIT
Pickup
Set the relay at the 0.5 time dial position and
minimum tap. Using the test connections of Figure
19 the main unit should close its contacts within
± 5% of tap value current.
Time Test
Set the relay at the 5.0 time dial position and
minimum tap. Using the test connections of Figure
19, and applying 5 times pickup current, the relay
should operate at 1.31 seconds ±7%. With 2 times
pickup current applied the operating time should be
7.21 seconds ±7%. With 10 times pickup current
applied the operating time should be 0.72 seconds
±7%.
B. INSTANTANEOUS UNIT
Pickup
With gradually applied current the unit should
pickup at ±10% of the minimum calibration. There
should be no more than ±5% variation on repeated
pickup checks. Be sure the target has been reset
after each test.
c. TARGET SEAL IN UNIT
Pickup
The unit should pickup between 75 and 100% of
tap value with the main unit contacts closed.
Dropout
Open the main unit contacts, the seal in unit
should remain picked up. Reduce the currentto 25%
of tap value; the unit should drop out.
RENEWAL PARTS
It is recommended that sufficient quantities of
renewal parts be carried in stock to enable the
prompt replacement of any that are worn, broken,
or damaged.
When ordering renewal parts, address the
nearest Sales Office of the General Electric Com-
pany, specify the quantity required and describing
the parts by catalogue numbers as shown in Renewal
Parts Bulletin No. GEF-3883.
15

GEH-1788 Type lAC Time Overcurrent Relay
1'-4--- 6 .625 _~
168MM
PANEL LOCATION
SEMI-FLUSH SURFACE
(2) 5/16-18 STUDS
FOR SURFACE MTG.
•
~TG. MTG
41
14---~------;i- ----f-a--" r------...,
9.125
232MM
I
GLASS
r)'\'--'----.-r./ Q
1/4 DRILL
4 HOLES
6MM~
2.187
56MM
4.375T
I11MM
, -
,
-
~I"
1 . 125 - _ I
29MM I
I
I
I
I
t
I
-It:- -1- --
CUTOUT
I
I
1
I
I
5.687
144MM
1
I
(4) 10-32 X 3/8
MTG. SCREWS
10-32
STUDS
I I U-
~ 6,187 iJ~M :13'OI~
~ 157MM 76MM
-
I
"'4.406
112MM
L
8.81
223M
2
M
I .218
~5MM II
PANELJiI
5/8 DRILL
2 HOLES
1 5MM------""I
.718
18MM
3/4 DRILL
10 HOLES
19MM
8.375
212MM
STUD
NUMBERING
9 7 5 3 1
00000
00000
10 8 6 ~ 2
BACK VI!::',!
CUTOUT MAY REPLACE
DRILLED HOLES
1.156
29MM
4.281
PANEL DRILL~NG
FOR
PANEL DRILLING
SEMI-FLUSH MOUNTING
FRONT VIE\.!
FOR SURFACE MOUNTING
FRONT VIEW
TYPICAL DIM.
INCHES
MM
3.0
I 76MM"'-
5/16-18 STUD
VIEW SHOWING ASSEMBLY OF HARDWARE
FOR SURFACE MTG. ON STEEL PANELS
Fig. 20 (K-6209271 [8]) Outline and Panel Drilling Dimensions for Relay Types IAC Relays
(11/91) (200)
GENERAL ELECTRIC CO., POWER SYSTEMS MANAGEMENT BUSINESS DEPT., MALVERN, PA. 19355
... :: ..
...