TIME-OVERCURRENT
TYPE lAC
RELAYS
INTRODUCTION
Type
Contact
Instantaneous
AC Trip
Induction
Outline
&
Internal
Circuits
Unit
IAC51A(-)A
One
NG
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
F
ig
.
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-e 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 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.
APPLICATION
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.
These
instructions do not purport to cover all details or variations in equipment nor to provide for
evt'ry possillle
c ontingenc y to be met in connection with installation, operation or maintenance.
Should
furt.'Jer
in
fo
r
ma
t
i o
n be
desired
or should particular problems arise
which
are not covered sufficiently for
the purchaser's
purposes,
t
h
e matter should be referred to the General
Electric
Company.
To
the extent req
u
ire
d the p
rodu
c
t
s
described herein meet applicable ANSI,
IEEE
and
NBMA
standards;
but
no
such
a
ss
u
r
a
n
c
e
is gi
v
e
n with
respect
to local codes a nd ordinances because they vary greatly.
3
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