GE IAC51A User manual

INSTRUCTIONS
TIME-OVERCURRENT RELAYS
TYPES
IAC51A IAC52A
IAC51B
IAC51R
IAC52 B
GENERAL _ ELECTRIC
GEH-1753J

GEH-1753 Time Overcurrent Relays Type IAC
2
TOP PIVOT ________ '-
TAP PLUG -----~~1f~II .. ~~~~~ .... --~~~;=:
SEAL-IN UNIT
HOLDING COIL
/""---TAP
BLOCK
SEAL-IN
~--"--_f_':-=Hrr_TI ME DIAL
TARGET-
._------+::-:
SEAL-IN UNIT
STATIONARY
CONTACT, LEFT
SEAL-IN UNIT
STATIONARY
CONTACT, RIGHT
SEAL -IN
MOVING
CONTACT
ASSEMBLV-- -, •
It 'III "'M"~ Io;f'S
~ ,!"'$T"'t.lLl1Qlt,fa
_: I ll1i~ • """"'lO-V!> UN!T
l-~ ~~, ,_. = !I
DISK
AND
SHAFT
LOWER
JEWEL SCREW
<&.1
A - (8006996) Front View
B - (8006997) Rear Vie,,,
DISK
DRAG
"---1-- MAGNET
Figure 1. The 1nduction lnit for Type lAC Relayso

TIME-OVERCURRENT
TYPE lAC RELAYS
INTRODUCTION
Type
Contact Instantaneous
AC Trip Induction
Outline & Internal
Circuits Unit
IAC51A(-)A One
NQ
IAC51B(- )A
One
Yes
IAC51R(- )A
One
Yes
IAC52A(-)A Two
No
IAC52B(- )A
Two
Yes
The Type lAC relays comprise a group of relays
that are employed to protect against overcurrent on
single-phase and polyphase circuits. The various
relays in this lAC group are identified by model
numbers, and the relays differ in the number of
circuits they close, the length of time delay and
features that are determined by the characteristics
of the protected circuit.
These relays consist of an induction unit or an
induction unit with an instantaneous unit which
Unit Unit
Panel Drilling
Connection
No One Fig. 18
Fig. 11
No
One
Fig. 18
Fig. 12
Yes
One
Fig. 18
Fig. 13
No
One
Fig. 18
Fig. 14
No
One
Fig. 18
Fig. 15
permits instantaneous tripping for extremely high
currents, 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 lAC
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 con-
venience, described separately in the following text.
The above table indicates the units comprising each
type and also lists the internal connections and out-
line and panel drilling diagrams.
INDUCTION
UNIT
INTRODUCTION
The induction unit is the basic unit in all lAC
relays. Fig. 1 shows the induction unit mounted in
the cradle. These units are of the induction-disk
construction type. The disk is actuated bya 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 tilne
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 tatches up and remains exposed until released
by pressing a button beneath the lower left corner
of the cover.
APPLICATIO N
The induction unit is the main unit in all lAC
relays, supplying the inverse time delay character-
istics 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-current
characteristics are shown in Fig. 2.
RATINGS
The induction element is designed to use any
one of three operating coils, each having a different
combination of taps as follows: 4, 5~ 6, 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 am-
peres.
Tilese instructions do not purport to cover all details or variations in equipment nor to provide for
every possihle contingency to be met in connection with installation, operation or maintenance. Should
further information he 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 JlO such assurance is gi ven wi th respect to local codes and ordinances because they vary greatly.
3

GEH-1753 Time Overcurrent Relays Type lAC
4
20
10
S
•
7
I
~ II
Z
o 4
~
III 3
2;i
~ 2
1
.S
.S
.1
.1
.11
.4
.3
.2
.1
.All
.DB
.07
.01
.05
.04
.03
.02
.01
~
1\ \
\\1\.
\\. I\.'\.
1\,
1\.'\
l"'-.
\\
I\.'-,
_"'-.
:"-
'\
'\ '\
"-
\ '\. '\
I\.
'"
"-
\. "-
."
,
"'-.
'\
"-
""
I'-..
\ ~
1"'-
"-
r-- .......
I'-..
i"-
f'... I'--.
\.
"-
"-I"-
r-- .....
'"
i'
f'...
r--~
l'----
\
"-
['-,1'-
f'-.
........
1'--1'-
~
r-.::
r--
r-......
r-
f'- f'....
t-
1-",
10
f--
~
I"
l"
f'-.
1'1'-
~
.............
r-..
r-......
r-
t"'-t--
9
t'-
I'--
r-.
t-
r-
I-
I'-t"'-
8
f"
I"-r--
1'--1'
r-..
r-
t--.
l-
t-- 7
f--
"
"- r---
r::--,
f--
'\.
......
I'-.
-......
---
r-
I~
f--
I"-
~t--
t"'-t--
II)
CJI
f--
"-
I"--
..............
---
I"-
IV
c
I\,
'"
I'-
I"---t--
1"-4
.-
f--
-
I--
I-
"-
.............
t-
-
f--
"
l"
--. 3
Q)
"-
r--
r-
(f)
f--
I .......
I--
.......
1-,....
1"-2
-
I--
r--",
----
c
.-
I--
r---.
--
r--
r-
0
r-
t-r-
I--
r--- I
Q)
t--
l"-
E
f--
rl"-
~
.-
t-
.1 .1 .1 .8 .8 1 2 3 4 II • 1 •• 10
20
30 40 50 80 7080 DO!
MULTlPLES OF RELAY TAP SETTING
Fig.2. (088880269 [3) Time-current Curves of Type lAC Relays with Inverse-time Characteristics

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:
DUAL RATED
0.2/2.0 0.6/2.0
0.2 2.0
0.6
2.0
Carry 30 amps for
(sec)
0.05 2.2
0.5
3.5
Carry 10 amps for
(sec) 0.45
20 5.0
30
Carry continuously
(amp)
0.37
2.3
1.2
2.6
Minimum operating
(amp)
0.2
2.0 0.6 2.0
Minimum dropout
(amp)
0.05
0.5 0.15 0.5
DC resistance
(ohms)
8.3 0.24
0.78 0.18
60 hertz impedance
(oh'TIs) 50
0.65
6.2
0.65
50 hertz impedance
(ohms)
42 0.54 5.1 0.54
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.
48
45
4.
39
}6
,
3J
--
30
¥
0
/
V
l 27
T
A
" 24
E
21
18
15
12
9
6
I VL
~
~
V/
V
~ / V
/;
V
I ~
/I V
,
~
:::::::::
~
~
::::-
3
0
~
-
~
~
Time Overcurrent Relays Type lAC GEH-1753
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. 3.
Coil
Amperes
4-16
1.5-6.0
0.5-2.0
I
/
/
/
/
/ /
'i
/
/'
/'
/ V
/
./
L V
V
f-;::: ~
::--
~
~
- --:::::
""""'"
Freq.
60
.....
50
'"
60
50
25
60
50
25
60
50
25
TAP
RANGE
.5-2.0
TAP
25"']
RANGE
60~ 1. 5-6. 0
50", ANPS.
]
TAP
60"'jRANGE
25", 4-16
50ft. ANPS.
Tap
Volt-
Imp.
PF
Amps
Ohms
4.0
8.8 0.35
0.29
4.0
8.0
0.32 0.31
4.0 7.5
0.30 0.36
1.5
59.0
2.36 0.26
1.5
52.0 2.08
0.28
1.5
48.0
1.92 0.34
0.5
530.0 21.2 0.26
0.5
470.0
18.8 0.28
0.5 430.0 17.2
0.34
o 4 6 8 10 12 14 16 18 20
MULTIPLES OF MINIMUM TAP SETTING
SATURATION CuRVES AT VARIOUS FREQUENCIES
FOR 3 TAP RANGES OF THE TYPE IACS1A RELAY
LOWEST TAP USEO IN ALL CASES
Fig. 3. (K-6306891-1) Saturation Curves for Lowest laps ',f the Induction Unit
of Type lAC Relays \vith Inverse-time r,haractcrislics.
5

GEH-1753 Time Overcurrent Relays Type IAC
50
51
DEVICE FUNCTION NUMBERS FOR USE
WITH ALL EXTERNAL DIAGRAMS
Instantaneous Unit
Overcurrent, Relay, Type IAC
51N -Ground Overcurrent Relay, Type lAC
52 Power Circuit Breaker
SI Seal-in Unit, with Target
TC
A
!
Trip Coil
Auxiliary contact, closed when breaker
closes.
A-C BUS
1
2
~
.li
~+~
~
j
M.l d I
~
" .~
t-
~ ~
rRIPPI~G -~
}l::1..
~ACTOR- ;
-L
l ~ t;T
-=-
1 1
Fi
6. 5
(K6375668-l) External Connections of Three
Type IAC51A Relays used in Conjunction with Tripping
Reactors for Protection of aTThree-Phase Circuit.
6
A_C BuS
1"I~rRIP BUS
W ll::2
ll=l
ill
ll.::l
I-I
28 t t
L
52
#
Fig. 4 (K-6375667-2) External Connections of Three
Type IAC5lA Relays used for Phase-to-Phase and
Ground Overcurrent Portection of a 3-Phase Circuit.
A-C Bus
Fig. 6 (K-6375669-6) External Connections of Three
Type IAC5lR Relays used for 3-Phase Circuit Protection.

Time Overcurrent Relays Type IAC GEH-1753
INSTANTANEOUS UNIT
INTRODUCTION
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. 7). 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 apredetermined value,
the instantaneous unit operates, closing the contact
[ircuit 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.
APPLICATION
The instantaneous unit is used on certain IAC
relay models to provide instantaneous tripping for
current exceeding a predetermined value.
OPERATING CHARACTERISTICS
The instantaneous element operates over a 4 to
1 range and has its calibration stamped on a scale
; ..
OPEAATING
COIL
.. TARGET
STATIONARY
CONTACTS
Fig. 7. (8006998) Type lAC Relay with an
Instantaneous Unit.
mounted beside the adjustable pole piece. Time-
current characteristics are shown in Fig. 10.
RATINGS
The instantaneous unit is designed to use either
of two coils having pickup ranges of 10 to 40, and
20 to 80 amperes respectively. The current-closing
rating of the contacts is 30 amperes for voltages
not exceeding 250 volts.
BURDENS
Burden data on the instantaneous unit coils are
given in the following table:
Coil Freq. Amp.
Volt
Imp.
Amp Ohms
10-40
60 5
0.83 0.033
50 5
0.80 0.032
25 5
0.65 0.027
20-80 60 5 0.21
0.008
50 5
0.20
0.008
25 5 0.15
0.007
SHORTING
COIL
---+-+--1:
MAl N -~~-.'--f---J
COIL
•
.. -=
Fig. 8. (8007060) Type lAC Relay with an
A-C Tripping Unit.
PF
0.95
0.95
0.98
0.95
0.95
0.98
-
7

8
GEH-1753
Time Overcurrent Relays Type IAC
A-C TRIPPING UNI1
INTRODUCTION
The a-c tripping unit is a Type REA relay unit
designed to energize a circuit breaker trip coil from
its assoc iated current transformer upon the operation
of the main unit of the IAC relay. It transfers the
current from the secondary of the current trans-
former 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
induction unit (see Fig. 8). The operation of this
unit is illustrated in Fig. 9. The secondary current
circulates through the induction unit current coil
and the main coil of the REA auxiliary tripping unit,
returning through the REA contacts to the current
transformer. Normally, most of the flux generated
by the main 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 REA is
short-circuited and current flows in this coil by
transformer action, causing a redistribution of flux
which actuates the armature and the REA contacts.
The opening of the REA contacts causes the secondary
current to flow through the trip coil which trips the
breaker.
0.030
0.025
•
~
en
0.0.20
I
&.U
::I
..-
O.Ol~
Q..
:;)
J:
u 0.010
CL
0.005
0 0 1 2 4
CURRENT
TRANS
16S1
BREAKER
TRIP COIL
L
AC TRIP UNIT
NORMALLY
CLOSlO
.-----------.:::1 oc;:;----+------<~ CONT ACTS
o
At:. TRIP UN~T
SHORTlhG
COIL
1-- __ -' ,..._-+_r=~~~r-::::::::t::J AC TRIP' UN IT
MAIN COIL
Figo 9 (K-6l54766-2) Diagram Illustrating Operatio~
of Type lAC Relays having an A-C Tripping Unit.
OPERATI NG TIME
RANGE FOR N4Y
PI CKUP SETIING
6 7 b 10
MULTIPLES Of PICK-UP
Fig. 10 (6306872 [5])
Time-current Characteristics of Original Instantaneous Unit

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
The a-c tripping unit has a continuous rating of
five
amperes but will operate on a minimum current
of 3.5 amperes. They 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 second-
ary current exceeds 100 amperes, the REAllB relay,
Time Overcurrent Relays Type IAC GEH-1753
which
has contacts rated 200 amperes, can be used
in conjunction with IAC overcurrent relays. The
REAllB is not mounted inside the IAC case.
BURDENS
Burdens of the REA unit are given in the
following table:
Frequency
Amp
Impedance
PF
Volt-
in Ohms
Amperes
60 5 0.49 0.80 12.2
50 5 0.33 0.85 8.4
25
5 0.23 0.62 5.8
RECEIVING, HANDLING AND STORAGE
These relays, when not included as a part of a
control panel, will be shipped in cartons designed
to ~rotect them against damage. Immediately upon
receipt of the relay, an examination should be made
for any damage sustained during shipment. If
injury or damage resulting from rough handling is
evident, a claim should be filed at once with the
transportation company and the nearest Sales Office
of the
General Electric Company notified promptly.
Reasonable care should be exercised in un-
SEAL-IN ~ UNIT ""'- I
D INDUCTION
UNIT
'"
l 1
f1
1
2 6
INTERNAL CONNECTIONS (FRONT
VIEW)o=SHORT FINGER
Fig. 11. (K-6209658-10) Internal Connections fo:
the Type IAC51A Relay (Front View).
packing the relay in order that none of the parts are
injured or the adjustments disturbed.
If the relays are not tobe installed immediately,
they should be stored in their original cartons 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.
2
INDUCTION
UNIT
INSTANT
UNIT
6
SHORT FINGER
Fig. 12. (K-6209661 [11) Internal Connections for
the Type IAC51B Relay (Front View)
9

GEH-1753 Time Overcurrent Relays Type IAC
10
SEAL-IN
iJ t; :
1
I
N U
S N
T :
A T
N
T
INDUCTION
Uf'i:-:-
I ~ I f1 ~ I ~ I
2 4 6 8 10
A-C -;RIP
- UN IT
INSTANT.
UU:
Fig. 13 (K-6209294-3) Internal Connections for the Type IAC5lR Relay (Front View)
SEAL-IN
UNIT
SI
INDUCTION
2
INDUCTION
UNIT
6
SHORT FINGER
Fig. 14 (K-6209662 [5]) Internal Connections for the Type IAC52A Relay (Front View)

SEAL-IN
UNIT
r1'
2
INDUCTION
UN IT
INSTANT.
UN IT
INSTANT.
UNIT
.. r
10
• * SHORT FINGER
Fig. 15 (K-6209663 [8]) Internal Connections for
the Type IAC52B Relay (Front View)
Time Overcurrent Relays Type IAC GEH-1753
TO TIMER
"STOP"
2
0
6 7
--
--
TC INDICATING LIGHT
WHEN CHECKING PICKUP
OF MAIN UN IT
-- --
---
TO INDICATING LIGHT WHEt
CHECKING PICKUP OF
INSTANTANEOUS UN IT
r---
- ---
6 0
3 4 5
0 0 0
8 9
10
x LA13 TEST PLUG
VARIABLE RESISTOR
TO TIMER
"START"
MIN. RECQI.t.4ENDED VOLTS,
120 AT RATED FREQUENCY
TO ACCURATELY REPRODUCE
RELAY CHARACTER I STI CS
ALL TESTS SHOULD BE
r,tAOE WI TH RELAY IN CASE.
Fig. 16 (K-6154399-7) Testing Connections for
Type lAC Relays such as Type IAC51A
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 diagrams are shown
in
Figs. 20 and 21.
CONNECTIONS
Internal connection diagrams for the various
relay types are shown in Fig. 11 to 17 inclusive.
Typical wiring diagrams are given in Fig. 4 to 6
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.
INSPICTION
At the time of installation, the relay should be
inspected for tarnished contacts, loose screws, or
other imperfections. If any trouble is found, it
should be corrected in the manner described under
MAINTENANCE.
CAUTION:
Every circuit in the drawout case has an auxi-
liary 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 secondary cir-
cuits from being opened.
CONNECTING PLUG MAIN BRUSH CONNECTING BLOCK
NOTE: AFTER ENGAGING AUXILIARY BRUSH, CONNECTING PLUG
TRAVELS 1/4 INCH BEFORE ENGAGING THE MAIN BRUSH ON
~HE TERMINAL BLOCK.
Fig. 17 (8025039) Cross Section of Drawout Case
Showing Position of Auxiliary Brush.
11

GEH-1753 Time Overcurrent Relays Type lAC
ADJUSTMENTS
TARGET AND SEAL-IN UNIT
For trip coils operating on currents ranging
from 0.2 up 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 currents ranging
from 2 to 30 amperes at the minimum control volt-
age, place the tap plug in the 2-ampere tap.
The tap screw is the screw hol.ding 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 station-
ary 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 neces-
sary 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 tap plug must not be removed without first
withdrawing the conneCting plug.
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 cur-
rent 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 screw driver 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 between 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 mini-
mum current within five percent of the tap-plug
setting. The unit resets at 90 per cent of the mini-
mum closing value.
TIME SETTING
The setting of the time dial determines the
length of time the unit requires to close its contacts
when the current reaches a 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 there-
fore thIs setting gives the maximum time setting.
12
The primary adjustment for the time of opera-
tion 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 disk shaft 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 in-
sure the proper sequence in the operatio~ of the
several circuit breakers. Allowance must l\le made
for the time involved in opening each break~r after
the relay contacts close. For this reason, unless
the circuit time of operation is known with accuracy,
there should be a difference of about 0.5 second (at
the maximum current) between relays whose opera-
tion is to be selective.
EXAMPLE OF SETTING
The time and current settings of the overcurrent
unit can be made easily and quickly. Each time value
shown in Fig. 2 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. 2,
insert the removable plug in the proper tap re-
ceptacle and adjust the time-dial to the proper
position. The following example illustrates the
procedure in making a relay setting.
Assume a Type lAC 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 1.9 secon<;is ona 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 amps. Since there is no 7.5-amp tap, the
8-amp. tap is used. To find the proper time-dial
setting to give 1.9 seconds time delay at 3750 am-
peres, divide 3750 by the transformer ratio. This
gives 62.5 amperes secondary current which is 7.8
times the 8-ampere setting. By referring to the
time current curves (Fig. 2), it will be seen that 7.8
times the minimum operating current gives 1.9
seconds time delay when the relay is set sl1ghtly
above the No.6 time-dial setting.
The above results should be checked by pleans
of an accurate timing device. Slight readjustment
of the dial can be made until the desired time is
obtained. .
Aid in making the proper selection of relay
settings may be obtained on application to the nearest
Sales Office of the General Electric Company.

CONTACT ADJUSTMENT
The contacts should have approximately 1/32
inch wipe. That is the stationary contact should be
deflected about l;:b inch when the disk completes
its travel. The contact wipe is adjusted by turning
the screws in the contact brush which regulates the
position of the brush, in relation to the brush stop.
For relays with two circuit-closing contacts, the
tips should be in the same vertical plane.
When the time dial is moved to a position where
the contacts just close, the time-dial scale should
indicate zero. If this is found incorrect, and the
brushes are correctly adjusted, regulate the dial to
read zero. This is done by changing the position of
the
arm attached to the shaft which fS located below
the
time dial. Loosen the screw which clamps the
arm to the shaft and turn the arm, relative to the
shaft, until the contacts just make at the zero time-
dial setting.
INSTANTANEOUS UNIT
Select the current above which is desired to
have
the instantaneous unit operate and set the ad-
justable pole piece so that the top of 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"
wipe. This adjustment can be made by loosening
the screws holdingthe 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:
Time Overcurrent Relays Type IAC GEH-1753
1. 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-i.nch
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 com-
pound bushing should be approximately 1/32 - inch
from the inner edge of the stationary contact sup-
porting post.
2. ARMATURE ADJUSTMENT
Loosen the two screws whichhold 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 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 re-
turn 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 andpole
face of the lower core after the unit operates may
cause contacts to open momentarily, 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. Excessive pressure on the arma-
ture, 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 ad-
justment has been obtained.
OPERATION
Before the relay is put into service it should be
given a check to determine that factory adjustments
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.
The pickup 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 above
test are shown in Fig. 18.
MAINTENANCE
The relays are adjusted at the factory and it is
advisable not to disturb the adjustments. If, for any
reason, they have been disturbed, the following points
should be observed in restoring them:
DISK AND BEARINGS
The lower jewel may be tested for cracks by
exploring its surface with the point of a fine needle.
If it is necessary to replace the jewel a new pivot
should be screwed into the bottom of the shaft at
the shaft at the same time. 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.
13

GEH-1753 Time Overcurrent Relays Type lAC
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 scratches 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 above can be
obtained from the factory.
PERIODIC TESTING
An operation test and inspection of the relay at
least once every six months are recommended. Test
connections are shown in Fig. 18.
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.
pany, specify quantity required, name of part wanted,
and give complete nameplate data. If possible,
give the General Electric Company requisition
number on which the relay was furnished.
When ordering renewal parts, address the
nearest Sales Office of the General Electric Com-
For a recommended parts list refer to Parts
Bulletin number GEF-3883.
HI SEI94IC AAlB)'IMSTMTMBUS "IT
~ERATING TIME
.025
,,.(I!(}
, ..
\
"-
OPEIlATI N& TI ME
I---
1\
~,
RANGE FOR ANY
V-
PI ClWP SETT I MCi
10
'~
8
0: .0
~'--
I
5 "-
.00
r--...
-'--
--
I I
1 1
1.5 2 3 5 7 8 9
10
J<lUL 1'1 PlES OF PICKUP
Fig. 19 (0208A8695 (l. J) Time-Current Characteristics for the "Hi-G" Unit
Since the last edition, Figures 12 and 14 have been revised.
14

Time Overcurrent Relays Type IAC GEH-1753
SENI-FlUSH--PANEL LOCHION_
IITG.
~G' _'_6_~ ___ o~~
I r--------
SURFACE
"'TG.
1
'f=,==:::;~====::::1! fe--1B STUDS FOR
SURFACE "'Tt..
STUD NU"'BER I NG
<RONT VIEW
FIG. -A
A
, 1 3 5
I
iOOO
~9_Q----"
~ DRILL
5 HO LE S
/
!
hi f, f --#'--J....jL.. ,~
I I 1- ._-.-=::::3
.-
... 0
11<'"
---- ~~
;~~~:;;;:::=~I~ :::Y---- "''''
11.---- (\'\0
T SI
r
:mro-
1
--··-
NUN .. BE E.RR. I N.G. . RE LAY
.£..t.G._. ...2..YfE...... __
i_A I AC51A
1 ). __ - _~c51B ~ ___ -
A I AC51C
A I AC52A
B IAC51R
B IAC52B I
OUTLINE
r
10-32 x J/8 NTG.
SCREW
STUD NU"'BER I HG
FRONT VI EW
FIG. -B
._---
B
II 1 J 5 7 9
1°0000
",-00000
2 4 6 8 10
PANEL RILLING
SENI-FL SH MTG.
FIG.A&B
VIEW SHOWING ASSEIIBlY OF
HARDWARE FOR SURFACE "'TG.
ON STEE l PANE LS.
~ DR ILL
2 HOLES J DRILL
~ . '" """"
r
-¥~-· lL
~ 1 th _ II<~
" --y- "'-~ !;~
"'.L. .' - ,.
~I 1-8
. 9~r 2~
~1j1 I B.
f--- 2~ --L... 25
L--....!. 5!' 8
4
PANEL OR IL LI HG
FOR FIG.S
SURF .CE "TO. -FROH VI~.
>'ig. 18 (237C707-1) Outline and Panel Drilling for the Type IAC51A, IAC51B, IAC51R, IAC52A and IAC52B Relays
15

å
åå
å
*( 3RZHU 0DQDJHPHQW
215 Anderson Avenue
Markham, Ontario
Canada L6E 1B3
Tel: [phone]
Fax: [phone]
www.ge.com/indsys/pm