GE IAC57A - Page 5

TIME
-
OVERCURRENT
RELAYS
TYPE
IAC
INTRODUCTION
Contact
Circuits
Instantaneous
Unit
AC
Trip
Outline
&
Panel
Drilling
Induction
Unit
Internal
Connection
Type
Unit
One
One
One
Two
Two
IAC
51
A
(
-
)
A
IAC
51
B
(
-
)
A
IAC
51
R
(
-
)
A
LAC
52
A
(
-
)
A
IAC
52
B
(
-
)
A
No
One
One
One
One
One
Fig
.
11
Fig
.
12
Fig
.
13
Fig
.
14
Fig
.
15
No
Fig
.
18
Fig
.
18
Fig
.
18
Fig
.
18
Fig
.
18
Yes
Yes
No
Yes
No
No
Yes
No
The
Type
IAC
relays
comprise
a
group
of
relays
that
are
employed
to
protect
against
overcurrent
on
single
-
phase
and
polyphase
circuits
.
The
various
relays
in
this
IAC
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
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
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
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
APPLICATION
The
induction
unit
is
the
main
unit
in
all
IAC
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
.
The
induction
unit
is
the
basic
unit
in
all
IAC
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
.
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
.
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
.
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
.
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
.
When
the
These
instructions
do
not
purport
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
.
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
given
with
respect
to
local
codes
and
ordinances
because
they
vary
greatly
.
Should
3
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