I�
TIME OVERCURRENT
TYPE lAC
RELAYS
INTRODUCTION
Type
Contact
lnstant .. ne-
Circuits
ous Unit
IAC51A(-)A
One
No
IAC51B(-)A
One
Yts
!AC51C
r
A
One
No
IAC51D- A
One
No
IAC51F-
A
One
Yes
IAC54A- A
Two
No
IAC5;�B- A
Two
Yes
The Type lAC relays comi)rise
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 r eI a y s differ in the number of
circuits they close, the
1
e n g t
h of
time de lay 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 element which
permits instantaneous tripping for extremely high
currents, or an induction unit with an a -c tripping
element 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
element and the a-c tripping element -they are for
convenience, described 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.
The case is suitable for either surface or semi
flush panel mounting and an assortment of hardware
is provided for either mounting. The cover attaches
to the case and also carries the reset mechanism
when one is required. Each cover screw has pro
vision for a sealing wire.
The case has studs or s c r e w connections at
both ends or at the b o t t o m only for the external
connections. T h e electrical connections between
the relay units and the case studs are made through
spring backed contact fingers
mounted
in
s
t
a
t
ion
a
r
y
Outline
AC
'ftitl
Induction
and
lntern,il
Unit
Unit
Panel
Connection
Drilling
No
One
Fig.
19
Fig.
11
No
One
Fig.
19
Fig.
U
Ye;;
One
Fig.
19
1-'ig.
13
No
Three
Fig.
20
Fig.
14
Ye�
One
Fig.
19
Fig.
15
No
No
One
Fig.
19
Fig.
16
One
Fig.
19
Fig.
17
molded inner and outer blocks between which nests
a removable connecting plug which completes the
circuits. The o u t e r blocks, attached to the case,
have the studs for the external connections, and the
inner b
1
o c k s have the terminals for the internal
c anne ctions.
The relay mechanism is m o u n t e d in a steel
framework called the cradle and is a complete unit
with all leads being terminated at the inner block.
This cradle is held firmly in the case with a latch
at the top and the bottom and by a guide pin at the
back of the case. The c a s e s and cradles are so
constructed that the relay cannot be inserted in the
case u p s i d e down. The connecting plug, besides
making the electrical connections between the re
spective blocks of the cradle and case, also locks
the latch in place. The cover, which is fastened to
the case by thumbscrews, holds the connecting plug
in place.
To draw out the relay unit the cover is first
removed, and the plug drawn out. Shorting bars are
provided in the case to short the current transfor
mer cirucits. The latches are then released, and
the relay unit can be easily drawn out. To replace
the relay unit, the reverse order is followed.
A
separate testing plug can be inserted in place
of the connecting plug to test the relay in place on
the panel either from its own source of current and
voltage, or from other sources. Or, the relay unit
can be drawn out and replaced by another which has
been tested in the laboratory.
These instructions do not pc�rport to cover all details or variations in equipment nor to provide for every possible
contingency to be met in connection with installation, operation or maintenance. Should further information be desired
or should particular problems arise which ore not covered wlficiently for the J>¥rchoser's pc�rposes, the matter should
be referred to the General Electric Company.
3
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