Westinghouse DH User manual

I
.
B
.
32
-
251
-
3
MAINTENANCE
RECEIVING
OPERATION
INSTRUCTIONS
De
-
ion
®
CIRCUIT
BREAKER
Type
DH
AIR
Horizontal
Drawout
Indoor
and
Outdoor
Service
INTERRUPTING
RATINGS
—
AMPERES
VOLTAGE RATINGS
3
-
PHASE
INTER
-
RUPTING
RATING
AMPERES
CONTIN
-
AIR
—
i
CIRCUIT
BREAKER
Min
.
KV
.
for
Rated
uous
Max
.
Design
At
Rated
Max
.
Amperes
60
CYCLES
TYPE
Rated
MYA
.
KV
.
INT
.
KV
.
Voltage
MVA
.
50
-
DH
-
150
-
E
50
-
DH
-
150
-
E
3.5
1200
150
4.16
4.76
21
,
000
21
,
000
35
,
000
35
,
000
25
,
000
25
,
000
37
,
500
37
,
500
4.16
4.76 3.5
2000
150
50
-
DH
-
250
-
E
50
-
DH
-
250
-
E
4.16
4.76 3.85
1200
250
4.16 4.76
3.85
2000
250
WESTINGHOUSE
ELECTRIC
CORPORATION
SWITCHGEAR
DIVISION
EAST
PITTSBURGH
,
PA
.
FEBRUARY
,
1959
EAST
PITTSBURGH
PLANT
NEW
INFORMATION
Printed
in
U
.
S
.
A
.
Courtesy of NationalSwitchgear.com

TABLE
CONTENTS
DESCRIPTION
Part
One
Description
.
Pages
5
-
7
5
RECEIVING
,
HANDLING
AND
STORING
Part
Two
Receiving
.
Handling
.
Storing
.
.
.
Weights
.
.
Page
8
8
8
8
8
OPERATION
Part
Three
Operation
Mechanism
Mechanism
Panel
Shunt
Trip
Magnet
Cut
-
Off
Switch
Contact
Position
Indicator
Interlock
Position
Indicator
Operation
Counter
Auxiliary
Switch
Latch
Check
Switch
Undervoltage
Trip
Attachment
.
...
Three
-
Coil
Trip
Attachment
Contacts
Arc
Chutes
Levering
-
In
Device
Test
Position
Operating
Position
Interlock
Secondary
Contacts
Ground
Contact
Puffer
Assembly
Mechanism
Operated
Control
Switch
.
Secondary
Control
Wiring
Pages
8
-
22
8
8
9
9
11
11
11
12
12
12
12
12
13
16
17
19
20
20
20
21
21
22
22
INSTALLATION
Part
Four
Installation
Pages
22
-
25
22
ADJUSTMENT
Part
Five
Mechanism
Tripping
Latch
Cut
-
Off
Switch
Latch
Check
Switch
.
Contacts
Pages
25
-
26
25
25
25
25
26
MAINTENANCE
Part
Six
Maintenance
Contacts
Moving
Contact
Assembly
.
Stationary
Main
Contact
.
.
.
Stationary
Arcing
Contacts
Arc
Chutes
Broken
or
Cracked
Ceramic
Parts
.
Pages
26
-
30
26
26
27
27
..
..
27
27
28
3
Courtesy of NationalSwitchgear.com

MAINTENANCE
(
Continued
)
Pages
26
-
30
Part
Six
Erosion
of
Ceramics
.
.
Dirt
in
Arc
Chute
Cleaning
Arc
Shields
Operating
Mechanism
.
Lubrication
Clearances
Puffer
Puffer
Nozzle
Auxiliary
Switch
Insulation
28
28
28
28
28
29
29
30
30
30
PARTS
IDENTIFICATION
Pages
30
-
34
Part
Seven
Parts
Identification
Identification
Photographs
Fig
.
25
Moving
Contact
Assembly
.
.
Fig
.
26
Stationary
Contact
Assembly
Fig
.
27
Mechanism
Assembly
Fig
.
28
Puffer
Assembly
Fig
.
29
Auxiliary
Switch
Renewal
Parts
30
31
31
32
33
34
34
30
LIST
OF
ILLUSTRATIONS
Page
Figure
Type
50
-
DH
-
250
-
E
,
1200
Amp
.
Breaker
,
Completely
Assembled
Type
50
-
DH
-
250
-
E
,
1200
Amp
.
Breaker
,
Completely
Assembled
,
Rear
View
Type
50
-
DH
-
250
-
E
,
1200
Amp
.
Breaker
with
Barrier
Removed
,
Front
View
Type
50
-
DH
-
250
-
E
,
1200
Amp
.
Breaker
,
with
Barrier
Removed
and
Arc
Chutes
Tilted
Back
for
Inspection
Solenoid
Operating
Mechanism
Solenoid
Operating
Mechanism
.
Diagram
of
Tripping
Positions
Mechanism
Front
Panel
Undervoltage
Trip
Unit
Type
50
-
DH
-
150
-
E
,
1200
Amp
.
Breaker
Contacts
Viewed
from
Rear
Type
50
-
DH
-
250
-
E
,
1200
Amp
.
Breaker
Contacts
Viewed
from
Rear
Type
50
-
DH
-
150
-
E
/
250
-
E
,
2000
Amp
.
Breaker
Contacts
Viewed
from
Rear
Type
50
-
DH
-
150
-
E
,
1200
Amp
.
Breaker
Contacts
Viewed
from
Front
Type
50
-
DH
-
250
-
E
,
1200
Amp
.
Breaker
Contacts
Viewed
from
Front
Type
50
-
DH
-
150
-
E
/
250
-
E
,
2000
Amp
.
Breaker
Contacts
Viewed
from
Front
Arc
Chute
Arrangement
Partially
Assembled
Arc
Chutes
Levering
-
In
Device
in
Position
for
Rolling
into
Cell
Levering
-
In
Device
with
Arms
in
Position
taken
when
Breaker
is
in
Operating
Position
in
Cell
View
of
Lower
Part
of
Breaker
from
Rear
Operating
Secondary
Contacts
Secondary
Contacts
Extended
for
Completing
Control
Circuits
when
Breaker
is
in
Test
Position
"
M
-
O
-
C
"
Switch
Operating
Arm
Diagram
of
Breaker
Internal
Wiring
Type
50
-
DH
-
150
-
E
/
250
-
E
Contact
Adjustment
Type
50
-
DH
-
150
-
E
,
1200
Amp
.
Moving
Contact
Assembly
Type
50
-
DH
-
150
-
E
,
1200
Amp
.
Stationary
Contact
Assembly
Mechanism
Assembly
Puffer
Assembly
Type
W
Auxiliary
Switch
Details
2
1
5
2
6
3
4
7
9
5
10
6
11
7
12
8
13
9
14
10
14
11
15
12
15
13
16
14
.
17
15
18
16
18
17
18
18
19
19
20
20
21
20
21
22
22
23
23
24
31
25
32
26
33
27
34
28
34
29
s
4
Courtesy of NationalSwitchgear.com

\
FIO
.
1
.
Type
50
-
DH
-
250
-
E
,
1200
Ampere
Breaker
,
Completely
Assembled
One
of
the
outstanding
improvements
in
modern
power
distribution
has
been
the
development
of
the
air
circuit
breaker
by
Westinghouse
for
distribution
circuit
voltages
.
On
circuits
where
the
duty
on
breakers
is
heavy
,
long
life
with
a
minimum
of
maintenance
makes
the
De
-
ion
air
breaker
an
outstanding
performer
.
In
the
type
DH
magnetic
De
-
ion
air
circuit
breakers
,
Westinghouse
offers
a
complete
standard
line
for
circuits
from
2.3
to
15
kv
.
Each
of
the
type
DH
air
circuit
breakers
is
three
-
pole
,
electrically
operated
,
and
is
built
as
a
complete
horizontal
drawout
unit
for
metal
-
clad
switchgear
.
Breaker
units
of
the
same
rating
are
interchangeable
so
that
changing
breakers
is
a
matter
of
minutes
.
Since
they
are
drawn
out
horizontally
,
no
lowering
or
lifting
is
necessary
.
Steel
barriers
and
automatic
interlocks
prevent
contact
with
live
parts
while
the
breakers
are
being
changed
.
As
in
the
case
of
most
high
voltage
electrical
equipment
,
these
breakers
should
be
inspected
and
maintained
at
regular
intervals
in
order
to
obtain
the
most
dependable
performance
.
2
Courtesy of NationalSwitchgear.com

PART
ONE
The
type
50
-
DH
-
150
-
E
and
50
-
DH
-
250
-
E
air
cir
-
cuit
breakers
are
three
-
pole
,
electrically
operated
,
horizontal drawout
units
for
use
in
metal
-
clad
switch
-
gear
.
The
ratings
of
the
breakers
are
tabulated
on
page
1
.
Figure
1
shows the
front
and
right
side
of
a
type
50
-
DH
-
250
-
E
breaker
completely
assembled
,
while
Fig
.
2
shows the breaker
from
the left
rear
ready
to
be
placed
in
the
cell
.
Figure
3
is
the
same
breaker
with
the
main
barrier removed
,
and
shows the
center
-
coil
arc
chutes
in
their
operating
positions
.
Part
of
the
separating
contacts
,
primary
disconnect
-
ing
contacts
,
insulated
operating
rods
,
auxiliary
switch
and
part
of
the solenoid
operating
mecha
-
nism
are
visible
.
These
components
are
supported
on
a
welded steel
frame
which
is
mounted
on
flanged
wheels
for
rolling
into
the
metal
-
clad cell
.
In
the lower
part
of
the
frame
is
located
the
levering
-
in
device
for
moving
the
breaker
into
final
contact
engagement
.
This
is
interlocked with
the
mecha
-
nism
to
prevent
inserting
or
withdrawing
the
breaker
with the
contacts
closed
,
and also
prevents
closing
the
contacts
unless the
breaker
is
completely
in
or
completely
out
of
the
cell
.
Also
located
in
the lower
part
of
the
frame
are
the
auxiliary
switch
,
shunt
trip
,
cut
-
off
switch
,
latch check
switch
,
operation
counter
,
breaker
contact
position
indicator
,
levering
-
in
de
-
vice
position
indicator
,
socket
for
maintenance
closing
lever
,
and
secondary
contacts
for
automati
-
cally
disconnecting
the control
wiring
when
the
breaker
is
in
the
withdrawn
position
.
The
arc
chutes
on
this
breaker
are
of
the
center
-
coil
design
in
which
the
magnetic
circuit is
H
-
shaped
with
the
cross
member
of
the
H
passing
through
the
center
of
the
arc
chute
.
The
blowout
coils
are
wound around the
cross
member
of
the
H
,
and
are
located
inside the
arc
chute
jacket
.
With
this
arrangement
,
the blowout
magnet
becomes
an
integral
part
of
each
arc
chute
assembly
.
To
provide
accessibility
for
contact
maintenance
and
inspection
,
the
arc
chutes
are
hinged
at
the
rear
.
Figure
4
shows the breaker
with
the
arc
chutes
tilted
back
.
In
this
position
,
the
contacts
are
readily
available
for
inspection
and
maintenance
.
A
one
piece
barrier
assembly
is
placed
on
the
breaker
before
it
is
rolled
into
the
cell
.
The
front
sheet
is
of
one
-
eighth
inch steel
and
forms
a
ground
-
ed
barrier
between
personnel
and live
parts
when
the
unit
is
in
the cell
.
The
Type
50
-
DH
-
150
-
E
and
50
-
DH
-
250
-
E
air
cir
-
cuit
breakers
are
arranged
for
use
in
metal
-
clad
equipment
from
which
they
are
drawn
out
horizon
-
FIO
.
2
.
Type
50
-
DH
-
250
-
E
,
1200
Ampere
Breaker
,
Completely
Assembled
,
Rear
View
tally
.
The
series
E
breakers
are
interchangeable
with
the
series
D
breakers
of
the
same
rating
.
As
may
be
seen
in
Fig
.
3
,
all
parts
are
supported
on
a
steel
frame
with
four
wheels
,
equipped
with
roller bear
-
ings
,
to
facilitate
moving
the
breaker
.
The wheel
flanges
engage
with
rails
to
align
the
breaker
in
the
metal
-
clad cell
.
The
six
main
primary
conductors
project
hori
-
zontally
from
the
rear
of
the
breaker
,
and
are
sup
-
ported
and
insulated
by
Redarta
bushings
.
At
the
rear
of
these
main
conductors
are
the
primary
dis
-
connects
which
are
clusters
of
contact
fingers
ar
-
ranged
to
engage
the
primary
conductors
in
the
cell
.
5
Courtesy of NationalSwitchgear.com

DESCRIPTION
ARC
CHUTE
BLOWOUT
MAGNET
ARC
CHUTE
HINGE
SHUNT
CONNECTION
PRIMARY
DISCONNECTS
MOVING
CONTACT
ARM
SHUTTER
ROLLER
OPERATING
ROD
LEVERING
-
IN
DEVICE
ARM
TRIP
LEVER
LEVERING
-
IN
DEVICE
OPERATING
SHAFT
MECHANISM
PANEL
MAINTENANCE
CLOSING
HANDLE
SOCKET
FLANGED
WHEELS
FIG
.
3
.
Type
50
-
DH
-
250
-
E
,
1200
Ampere
Breaker
with
Barrier
removed
,
Front
View
6
Courtesy of NationalSwitchgear.com

DESCRIPTION
I
.
B
.
32
-
251
-
3
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
FIO
.
4
.
Type
50
-
DH
-
250
-
E
,
1200
Ampere
Breaker
,
with
Barrier
removed
and
Arc
Chutes
tilted
back
for
Inspection
7
Courtesy of NationalSwitchgear.com

PART
TWO
RECEIVING
,
HANDLING
,
STORING
All
Type
DH
breakers
are
assembled
and
given
operating
tests
at
the
factory
,
after
which
they
are
carefully
inspected
and
prepared
for
shipment
by
workmen
experienced
in
the
proper
handling
and
packing
of
electrical
equipment
.
The
complete
breaker
is
shipped
in
a
single
crate
.
The breaker
frame
is
located
at
the
front
of
the
crate
,
with the
interphase
barrier installed
.
The
three
arc
chutes
are
individually
packaged
and
are
located
at
the
rear
of
the
crate
.
After
the
equipment
has
been
unpacked
,
make
a
careful
inspection
for
any
damage
which
may
have
occurred
in
transit
.
If
the
apparatus
has been dam
-
aged
,
file
a
claim
immediately
with
the
carrier
and
notify
the
nearest
Westinghouse
Sales Office
.
HANDLING
Remove
the
crating
and
packing
carefully
.
To
avoid
damage
from
improper
handling
of
crow
-
bars
or
other tools
,
use
a
nail
puller
for
the
uncrating
.
Care
must
be used
in
handling
the
arc
chutes
since
the
splitter plates
in
them
are
made
of
a
ceramic
material
which
may
break
if
dropped
.
The
base
of
the
crate
may
be
used
as
a
skid
for
moving
the breaker
,
or
the
breaker
may
be
lifted
with
slings
under the
crate
.
If
the breaker
is
to
be
lifted
with
slings
,
move
it
while
it
is
still
crated
.
After
the
breaker
is
unpacked
,
the best
way
to
move
it
is
by
rolling
on
its
own
wheels
.
If
it
is
necessary
to
lift
the
breaker
after
it
is
un
-
crated
,
lift
it
without the
barrier
or arc
chutes
in
place
.
Slings
may
be
placed
under
the
breaker
frame
or
hooks
used
in
the
holes
provided
near
the
top
of
the
frame
.
STORING
The
arcing
chambers
are
shipped
in
separate
containers
located
at
the
rear
of
the
crate to
guard
against
damage
from
rough
handling
and
for
better
protection
from
dust
and
water
or
liquids
.
Store
them
in
their
shipping
containers
until
ready
for
use
.
Store
all
components
of
these breakers
in
a
clean
dry
place
.
During
the
storage
period
,
keep
them
sufficiently
warm
to
prevent
moisture
condensation
.
Table
of
Approximate
Weights
(
In
Pounds
)
BREAKER
WITHOUT
CHUTE
BREAKER
AMPERE
RATING
SINGLE
BARRIER
ASSEM
-
COM
-
TYPE
PLETE
BREAKER
ARC
&
CHUTE
BLY
BARRIER
50
-
DH
-
150
-
E
50
-
DH
-
150
-
E
1200
2000
695
85
80 1030
960
85
100
1315
50
-
DH
-
250
-
E
50
-
DH
-
250
-
E
1200
no
695
85
1110
2000
960
110
100
1390
PART
THREE
OPERATION
Before
placing
the
circuit
breaker
in
service
,
it
is
advantageous
to
become
familiar
with
the
con
-
struction
and
function
of
the
various
parts
which
are
described
in
the
following
paragraphs
.
This
material should be studied
carefully
.
The
general
arrangement
of
the breaker
com
-
ponents
is
shown
in
Fig
.
3
.
The solenoid
coil
is
built
to exert
a
horizontal
force
on
the
mechanically
trip
free
linkage
of
the mechanism
.
This
linkage
,
in
turn
,
exerts
an
upward
force
on
the three
insulated
oper
-
ating
rods which
act
on
the
moving
contact
arms
to
close the
contacts
.
The breaker has
two sets
of
contacts
:
the
main
contacts
for
carrying
the
con
-
tinuous
load
current
,
and
the
arcing
contacts
for
carrying
the
current
during
interruption
.
As
the
contacts
close
,
the
arcing
contacts
touch first
to
establish the
circuit
,
and then
the
main
contacts
follow closed
.
On
opening
,
the
main
contacts
separate
first
and
then the
arcing
contacts
follow
.
This
insures
that
the
main
contact
surfaces
will
re
-
main
free
of
burning
and
pitting
for
good
current
carrying
capacities
.
Above the
arcing
contacts
are
located the
center
-
coil
arc
chutes
for
extinguishing
the
arc
while
the breaker
contacts
are
separating
.
The
breaker
is
tripped
by lifting
the
primary
latch
either
manually
or
electrically
by
means
of
the
trip
coil
.
MECHANISM
The
solenoid
operating
mechanism
with
its
trip
-
free
linkage
is
shown
in
Fig
.
5
,
with the
operation
of
the
linkage diagrammed
in
Fig
.
6
.
In
this
mecha
-
nism
,
the horizontal
pull
of
the
solenoid coil
is
trans
-
mitted
to
the
contact
operating
rods
through
a
sys
-
tem
of
links which
rotate
counterclockwise
about
the
operating
center
.
This
linkage
system
consists
of four
major
links
:
the
non
-
trip
free
lever
,
trip
free
lever
,
upper
trip
free
link
,
and lower
trip
free
link
.
These
members
are
arranged
as
shown
and
are
held
8
Courtesy of NationalSwitchgear.com

I
.
B
.
32
-
251
-
3
OPERATION
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
CONTACT
POSITION
INDICATOR
CUTOFF
SWITCH
OPERATING
ARM
MECHANISM
STOP
BOLT
I
TRIP
LEVER
SOLENOID
BACK
PLATE
%
NON
-
TRIP
FREE LEVER
TRIP FREE
LEVER
LOWER
TRIP
FREE
LINKS
air
t
CLOSING
LINK
'
/
/
%
SOLENOID
COIL
t
l
CLOSING
LATCH
I
FIG
.
5
.
Solenoid
Operating
Mechanism
to
form
a
rigid
member
by
the
cam
link
and
tripping
cam
.
The
tripping
cam
is
prevented
from
rotating
by
the
tripping
latch
.
When
the
solenoid
is
energized
,
the
movable
core
pulls
on
the
junction
of
the
non
-
trip
free
lever
and
the
lower
trip
free
link
through
the
closing
link
.
This
causes
the
system
to
rotate
about the
operating
center
as
the
parts
move
from
the
RESET
POSITION
,
Fig
.
6
C
,
to
the
CLOSED
POSITION
,
Fig
.
6
A
.
The
trip
free
lever then
exerts
an
upward
force
on
the
three
operating
rods
to
close the
breaker
contacts
.
The
mechanism
linkage
is
held
in
this
position
by
the
closing
latch which
locks
on
a
pin
at
the
bottom
of
the
non
-
trip
free
lever
.
The
breaker
is
tripped
either
electrically
or manu
-
ally
by
lifting
the
primary
latch which
disengages
the
tripping
latch
.
This allows the
tripping
latch
to
rotate
counterclockwise
and
release
the
tripping
cam
so
that
it
is
free
to rotate
counterclockwise
.
Without
the
restraining
force of
the
cam
and
cam
links
,
the
upper
and lower
trip
free
links
collapse
under
the
force of
the
contact
springs
,
and
the
accelerating
springs
on
the
puffer
rods
.
The
junction
of
these links
moves
to
the
right
,
and
the
trip
free
lever
rotates
clockwise
opening
the breaker
contacts
.
The
position
of
the
linkage
is
then
as
shown
in
the
TRIP FREE
POSITION
,
Fig
.
6
B
.
In
moving
to
this
position
,
the lower
trip
free
link
presses
the
closing
latch
downward
,
and
disen
-
gages
the
pin
in
the
non
-
trip
free
lever
.
The
re
-
trieving spring
now
pulls
on
the solenoid
core
which
moves
the
linkage
and
the
tripping
cam
to
the
reset
position
as
shown
in
Fig
.
6
C
.
In
this
position
the
tripping
latch
is
reset
,
and
the breaker
may
be
reclosed
.
MECHANISM
PANEL
The mechanism
panel
is
mounted
on
the
front
of
the
closing
mechanism
as
shown
in
Fig
.
7
.
On
it
are
mounted the
following
auxiliary
devices
included
as
standard
on
all
breakers
:
Shunt
Trip
Magnet
.
The
shunt
trip
magnet
is
a
small
electromagnet
which
is
used
to
trip
the
»
9
Courtesy of NationalSwitchgear.com

OPERATION
,
FIG
.
6
.
Solenoid
Operating
Mechanism
—
Diagram
of
Tripping
Positions
10
Courtesy of NationalSwitchgear.com

I
.
B
.
32
-
251
-
3
OPERATION
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
CONTROL
MECHANISM
CUTOFF
SWITCH
STOP BOLT
BARRIER
MOUNTING
BRACKET
LEVERING
-
IN
DEVICE
OPERATING
SHAFT
9
POLE
AUXILIARY
SWITCH
OPERATION COUNTER
INTERLOCK POSITION
INDICATOR
LATCH
CHECK
SWITCH
CONTACT
POSITION
INDICATOR
TRIP
LEVER
MAINTENANCE
CLOSING
LEVER
SOCKET
SECONDARY
CONTACT
SLIDE
SHUNT
TRIP
MAGNET
FIO
/
7
JJ
Mechanism
Front
Panel
breaker
electrically
from
an
external
source
.
It
may
be
equipped
with
a
coil
for
direct
current
alter
-
nating
current
,
or
capacitor
tripping
.
When
the
shunt
trip
magnet
is
energized
,
the
moving
core
is
drawn
up
into
the
magnet
yoke
toward the
station
-
ary
core
.
An
extension
of
the
moving
core
protrudes
through
the
top
of
the
magnet
assembly
.
As
the
core
moves
up
,
this
extension
moves
against
the
trip
lever
directly
above
it
.
The
force
of
the solenoid
is
sufficient
to
raise
the
trip
lever
which
disengages
the
primary
latch
tripping
the
breaker
.
A
bracket
at
the
bottom
of
the
assembly
retains
the
moving
core
,
and limits
its
travel
to
about
%
inch
.
A
thin
brass
washer
prevents
the
moving
core
from
being
retained
by
residual
magnetism
in
the
raised
posi
-
tion
after
the coil
is
de
-
energized
.
Cut
-
Off
Switch
.
The
cut
-
off
switch
is
a
single
pole
normally
open
contact
which
acts
with the
breaker control
relays
to
cut
off
the
closing
coil
cur
-
rent
after
the breaker
is
closed
.
The switch
is
oper
-
ated
by
an arm
attached
to
the
trip
-
free
lever
in
the
mechanism
and
the
contact
remains
closed
as
long
as
the breaker
is
closed
.
Contact
Position Indicator
.
The
contact
posi
-
tion
indicator
gives
a
positive
indication
that
the
breaker
contacts
are
either
open
or
closed
.
It
oper
-
ates
directly
on
the
trip
-
free
lever
in
the
mechanism
.
Interlock
Position
Indicator
.
The
interlock
position
indicator
gives
a
positive
indication
of
the
position
of
the
breaker
interlock
.
It
operates
from
the
levering
-
in
device
shaft
.
When
the
indicator
points
to
the word
OPERATE
,
the interlock
is
free
and the
breaker
may
be
closed
or
tripped
.
When
the indicator
points
to
the word
INTERLOCKED
,
the
interlock
is
functioning
and the
breaker
cannot
be
closed
.
Since
the
interlock
is
operative
only
when
11
i
Courtesy of NationalSwitchgear.com

OPERATION
,
the breaker
is
in
an
intermediate
position
between
fully
engaged
and
fully
withdrawn
,
it
also
serves
as
a
means
of
indicating
that
the
breaker
is
in
the
Oper
-
ating
Position
and the
main
disconnecting
contacts
fully engaged
,
or
that
it
is
in
the
Test
Position
with
the
contacts
separated
.
Operation
Counter
.
The
operation
counter
records
each
operation
of
the
breaker
.
It
advances
one
count
for
each
tripping
operation
.
A
spring
type
link
from
the
trip
free
lever
operates
the
counter
.
Auxiliary
Switch
.
The
auxiliary
switch
is
a
nine
pole
rotary
type
,
and
is
operated
by
a
link
from
the
trip
free
lever
in
the
mechanism
.
There
are
five
"
a
"
contacts
(
closed
when the
breaker
is
closed
)
,
and
four
"
b
"
contacts
(
closed when the
breaker
is
open
)
.
These
are
arranged
alternately
,
starting
with
an
"
a
"
contact
nearest
the
operating
lever
.
The
first
and
third
segments
of
the
rotor
are
longer
than
the
others
,
and
are
connected
on
each
side
of
the shunt
trip
coil
.
When
the breaker
closes
,
these
complete
the
trip
coil
circuit
just
as
the
main
con
-
tacts
touch
.
The
rotor turns
approximately
90
°
,
and
is
adjusted
by
the
serrated
operating
lever
.
Each
contact
is
able
to
carry
20
amperes
con
-
tinuously
,
and
interrupt
the
following
current
FIG
.
8
.
Undervoltage
Trip
Unit
a
spring
during
the breaker
closing
stroke
to
lift
the
primary
latch
of
the breaker
mechanism
.
The
hold
-
ing
magnet
coil
may
be
directly
connected
to
a
d
-
c
control
source
,
or
it
may
be
supplied
with
low
volt
-
age
d
-
c
obtained
from
an a
-
c
control
voltage
through
a
small
transformer
and
Rectox
assembly
mounted
in
the
cell
structure
.
Normally
the
moving
core
of
the
device
is
held
magnetically
against
the
station
-
ary
core
to
hold
the rod and
consequently
the
reset
lever
in
the
reset
position
.
When
the
coil
voltage
is
reduced
sufficiently
,
the
reset
lever
spring
over
-
comes
the
magnetic
attraction
of
the
cores
and
rotates
the
reset
lever clockwise
.
As
the
reset
lever
rotates
,
the
pin
pushes
against
the
latch
to
release
it
from
its
latch
plate
.
When
the
latch
releases
,
the
trip
spring
rotates
the
trip
lever
to
trip
the
breaker
.
The
linkage
is
reset
by
the
trip
free
lever
of
the
mechanism
as
the breaker
opens
.
For
time
delay
release
on
tripping
,
a
very
high
resistance
coil
is
employed
in
the
holding
magnet
,
and
is
supplied
with
about
300
volts d
-
c
from
a
trans
-
former
,
Rectox
,
and
capacitor
device
mounted
in
the cell
.
The
capacitor
is
connected
across
the
coil
,
and
provides
a
slowly
decaying
holding
current
.
The
time
delay
is
adjusted
by
varying
the
charging
voltage
to
the
capacitor
by
a
four
step
resistor
,
giving
approximately
one
to
three
seconds
delay
.
Three
-
Coil
Trip
Attachment
.
The
three
-
coil
trip
attachment
,
when
supplied
,
mounts
on
the
mechanism
panel
and
is
used
in
addition
to
the
VOLTAGE
NON
-
INDUCTIVE INDUCTIVE
125
d
-
c
250
d
-
c
600
d
-
c
125
a
-
c
250
a
-
c
600
a
-
c
8
.
4
.
1
.
2
.
0.2
0.5
30
.
50
.
15
.
25
.
3
.
5
.
Latch
Check
Switch
.
The
latch
check switch
is
a
small
,
light
force
,
snap
action
switch which
is
operated
by
the
primary
latch
of
the mechanism
.
When
a
breaker
is
to
be
automatically
reclosed
after
being
tripped
free
,
the
links
in
the mechanism
must
be
completely
returned
to
the
Reset
position
before
the
closing
solenoid
is
energized
.
See
B
and
C
of
Fig
.
6
.
Since
the
primary
latch
is
the
last
part
of
the
mechanism
to reset
,
the
switch
will
hold
its
contact
open
until the latch
returns to
its
normal
position
.
In
addition
to
the
above
items
which
are
standard
on
all
breakers
,
the
following
special
devices
may
also be mounted
on
the
mechanism
panel
when
required
.
Undervoltape
Trip
Attachment
.
The
under
-
voltage
trip
attachment
,
shown
in
Fig
.
8
,
is
a
magnetically
held
device
which
will
trip
the breaker
when
its
control
voltage
drops
below
a
predeter
-
mined
value
.
This
device
uses
the
energy
stored
in
01
to
rR
12
Courtesy of NationalSwitchgear.com

I
.
B
.
32
-
251
-
3
OPERATION
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
STATIONARY
ARCING
CONTACT
UPPER
CONTACT
FOOT
MOVING
ARCING
CONTACT
STATIONARY
MAIN
CONTACT
FINGER
CONTACT
FINGER
SPRING
imk
MOVING
MAIN
CONTACT
FINGER
STOP
T
MOVING
CONTACT
ARM
PUFFER
NOZZLE
INSULATION
FIG
.
9
.
Type
50
-
DH
-
150
-
E
,
1200
Ampere
Breaker
Contacts
Viewed
from
Rear
shunt
trip
magnet
.
It
is
designed
to
accommodate
<
three
instantaneous
current
transformer
trip
assem
-
blies
.
The
calibration
of
each
current
trip
coil
is
engraved
with
the
values
of
current
required
to
trip
the
breaker
.
the
higher
interrupting
current
and
is
shown
in
Fig
.
10
.
For
both
the
50
-
DH
-
150
-
E
and
50
-
DH
-
250
-
E
rat
-
ings
,
the
2000
ampere
breakers
use
the
same
moving
contact
as
the
1200
ampere
Type
50
-
DH
-
250
-
E
breaker
.
However
,
four
moving
blades
are
employed
instead
of
two
,
and
five
contact
bolts
instead
of
three
.
The
four
blades
are
hinged
to
a
casting
on
the
lower
bushing
as
shown
in
Fig
.
11
.
All
contact
resiliance
is
built
into
the
stationary
contact
assembly
.
Because
of
the
high
momentary
rating
of
these
breakers
the
stationary
contacts
have
been
divided
to
give
multiplicity
of
contact
surfaces
.
The
1200
ampere
Type
50
-
DH
-
150
-
E
breaker
employs
four
movable
fingers
for
the
main
con
-
tact
,
each
backed
by
a
separate
finger
spring
.
Each
has
a
silver
inlay
that
mates
with
the
moving
main
contact
.
The
stationary
arcing
contact
is
located
directly
above
.
See
Fig
.
12
.
The
1200
ampere
Type
50
-
DH
-
250
-
E
breaker
stationary
contact
is
shown
in
Fig
.
13
and
is
similar
with
the
exception
that
the
arcing
contact
is
wider
.
The
2000
ampere
rating
employs
six
fingers
on
each
stationary
contact
,
and
is
shown
in
Fig
.
14
.
Cooling
fins
are
located
on
each
side
of
the
contact
.
With
this
contact
design
,
all
current
breaking
and
interrupting
parts
are
completely
enclosed
by
the
arc
chutes
.
CONTACTS
Each
pole
of
the
type
50
-
DH
-
150
-
E
and
50
-
DH
-
250
-
E
breakers
is
equipped
with
both
main
and
arcing
contacts
.
When
the
breaker
is
tripped
,
the
main
contacts
separate
first
and
then
the
arcing
contacts
follow
.
When
the
breaker
is
closed
,
they
make
up
in
the
reverse
order
.
For
the
1200
ampere
rating
,
the
body
of
the
mov
-
ing
contact
is
a
copper
forging
to
which
is
brazed
the
main
contact
inlay
.
This
assembly
is
bolted
be
-
tween
two
formed
copper
blades
which
hinge
on
the
lower
bushing
foot
and
form
the
moving
contact
arm
.
See
Fig
.
9
.
These
are
moved
between
the
closed
and
open
positions
by
the
mechanism
through
the
Redarta
operating
rods
.
The
load
current
is
con
-
ducted
across
the
hinge
through
silver
electro
-
plated
surfaces
,
with
pressure
being
supplied
by
spring
washers
on
either
side
.
The
moving
arcing
contact
is
hinged
to
the
top
of
the
main
contact
and
the
arcing
current
is
carried
by
means
of
a
flexible
shunt
inside
the
assembly
.
For
the
type
50
-
DH
-
150
-
E
breaker
the
moving
arcing
contact
consists
of
a
single
casting
with
a
silver
-
tungsten
inlay
.
See
Fig
.
9
.
On
the
Type
50
-
DH
-
250
-
E
breaker
,
this
contact
is
divided
for
carrying
i
13
Courtesy of NationalSwitchgear.com

OPERATION
,
UPPER
CONTACT FOOT
STATIONARY
ARCING
CONTAC
I
STATIONARY
MAIN
CONTACT
FINGER
MOVING
ARCING
CONTACT
!
CONTACT
UNGER
SPRING
?
if
INSULATION
MOVING
MAIN
CONTACT
1
T
PUFFER
NOZZLE
MOVING
CONTACT
ARM
FIG
.
10
.
Type
50
-
DH
-
250
-
E
,
1200
Ampere
Breaker
Contacts
,
Viewed
from
Rear
MOVING
ARCING
CONTACTS
P
U
F
F
E
R
STATIONARY
ARCING
CONTACT
UPPER
CONTACT
FOOT
MOVING
MA
CONTACT
MOVING
CONTACT
ARMS
:
INNER
&
OUTE
FIG
.
11
Type
50
-
DH
-
150
-
E
/
250
-
E
,
2000
Ampere
Breaker
Contacts
,
Viewed
from
Rear
Courtesy of NationalSwitchgear.com

I
.
B
.
32
-
251
-
3
OPERATION
.
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
UPPER
CONTACT
FOOT
STATIONARY
ARCING
CONTACT
MOVING
ARCING
CONTACT
.
STATIONARY
MAIN
CONTACT
FINGERS
(
4
)
ARCING
CONTACT
EYE
BOLT
MOVING
CONTACT
ARM
ARCING
CONTACT
—
SPRINGS
i
0
:
}
FIG
.
12
.
Type
50
-
DH
-
150
-
E
,
1200
Ampere
Breaker
Contacts
,
Viewed
from
Front
STATIONARY
ARCING
CONTACT
UPPER
CONTACT
F
001
STATIONARY
MAIN
CONTACT
FINGERS
(
4
)
MOVING
ARCING
CONTACTS
ARCING
CONTACT
EYE
BOLT
MOVING
CONTACT
ARM
ARCING
CONTACT
SPRINGS
FIG
.
13
.
Type
50
-
DH
-
250
-
E
,
1200
Ampere
Breaker
Contacts
,
Viewed
from
Front
Courtesy of NationalSwitchgear.com

OPERATION
,
STATIONARY
„
f
ARCING
CONTACT
STATIONARY
MAIN
CONTACT
FINGERS
(
6
)
MOVING
ARCING
CONTACTS
^
ARCING
CONTACT
EYE
BOLT
ARCING
CONTACT
SPRINGS
MOVING
CONTAC
1
ARMS
:
INNER
&
OUTER
CONTACT
FOOT
FIG
.
14
,
Type
50
-
DH
-
150
-
E
/
250
-
E
,
2000
Ampere
Breaker
Contacts
,
Viewed
from
Front
ARC
CHUTES
The
arc
chute
consists
of
an
H
-
shaped
blow
-
out
magnet
,
blow
-
out
coils
,
transfer
arc
horns
,
transfer
slacks
,
main
interrupter
stacks
,
a
front
arc
horn
,
and
a
rear
arc
horn
all
assembled
in
and
about
a
fabri
-
To
either
side
of
the
main
interrupter
stacks
are
two
metallic
arc
horns
to
which the
arc
transfers
from
the
arcing
contacts
.
The
front
arc
horn
is
con
-
nected
electrically
to
the
moving
contact
,
and the
rear
arc
horn
is
connected
to
the
stationary
contact
.
The
action
of
a
breaker
in
interrupting
an
arc
is
as
follows
.
Referring
to
Fig
.
15
,
when the
arcing
contacts
part
and
an
arc
is
drawn
,
it
loops
up
and
impinges
on
the
lower ends
of
the
two
transfer
arc
horns
and the
shading
coil
.
The
two
short
segments
of
the
arc
,
from
the
transfer
arc
horns
to
the
shading
coil
,
then
move
up
into
the
transfer
stacks
and
are
quickly
interrupted
placing
the
blow
-
out
coils
in
series
with
the
arc
.
When
the
current starts to
flow
in
the blow
-
out
coils
,
a
magnetic
field
is
established
and
the
arc
,
which
by
this
time is
two
separate
arcs
extending
from
the
front
and
rear
arc
horns
to
the
transfer
horns
,
is
driven
very
rapidly
into
the
slots
of
the
refractory
plates
of
the
main
interrupter
stacks under
the
influence
of
the
powerful
magnetic
force
.
As
the
arc
moves
to
the closed end
of
the
slots
,
it
is
restric
-
ted
,
lengthened
,
and cooled
.
All
of
these
forces
re
-
sult
in
rapid
de
-
ionization
of
the
arc
space
;
and
for
the
arc
to
maintain
itself
,
it
must
continuously
ionize
fresh
gas
.
At
current
zero
the formation
of
new
ioni
-
zation
momentarily
ceases
,
but
the de
-
ionization
con
-
tinues
so
that
dielectric
strength
is
established
in
the
arc
space
and the
circuit is
interrupted
.
i
cated
rectangular
Redarta chute
jacket
.
The
arc
chute
is
hinged
to
the
breaker
;
and when
it
is
in
the
normal
position
,
its
lower end
completely
surrounds
the
contact structure
.
Fig
.
15
is
a
schematic
cross
section
of
the
arc
chute
showing
the
component
parts
.
The
blow
-
out
magnet
is
located
so
that
the
core
passes
through
the
center
of
the
arc
chute
.
A
blow
-
out
coil
is
wound
near
each
end
of
the
core
and
lays
in
a
window
cut
in
the
side sheet
of
the
chute
jacket
.
One
terminal
of
each
coil
connects
to
a
transfer
,
or
center
arc
horn
,
and
the
other terminals
are
joined
at
the
top
of
the
shading
coil
.
Two
transfer
stacks
are
placed
in
the
space
between the
transfer
arc
horns
and
the
shading
coil
.
To
either
side
of
the
transfer
arc
horns
are
the
main
interrupter
stacks
which
are
made
up
of
a
series
of
insulating
refractory
plates
.
These
plates
have
inverted
V
-
shaped
slots
molded
into
them
.
The slots
are
offset
so
that
when
the
plates
are
stacked
with the
slots
alternating
from
one
side
to
the other
,
the
arc
must
take
a
serpentine
path
as
it
moves
up
into
the
arc
chute
increasing
the
length
of
the
arc
and
at
the
same
time
restricting
the diameter
of
the
arc
.
©
i
16
Courtesy of NationalSwitchgear.com

I
.
B
.
32
-
251
-
3
[
ON
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
I
Arc
Ch
:
v
:
IRING
-
IN
D
;
VICE
of
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sembl
-
DH
.
>
rrl
of
fk
tin
uell
Th
<
ick
rea
tee
break
the
pr
<
>
vided
beer
5
imil
pa
ea
<
ea
<
baft
ba
<
bee
red
on
On
each
roll
.
of
th
-
rpe
ral
]
th
<
Courtesy of NationalSwitchgear.com

OPERATION
»
'
•
TYPE
50
-
DH
-
150
E
TYPE
50
-
DH
-
250
E
FIG
.
16
.
Partially
Assembled
Arc
Chutes
place
the
crank
on
the
operating
shaft
at
the
front
right
corner
of
the
breaker
(
Refer
to
Fig
.
3
)
push
in
,
and
rotate
to
engage
the
coupling
in
the
levering
-
in
device
.
The
breaker
contacts
must
be
open
to
en
-
gage
the
coupling
,
and
the
indicator
will
show
"
In
-
terlocked
"
.
Rotate
the
crank
counterclockwise
to
the
end
of
the
travel
.
During
this
time
the
interlock
me
-
chanism
will
hold
the
coupling
engaged
.
At
the
end
of
the
travel
,
the
interlock
will
release
,
the
crank
will
move
to
the
front
,
and
the
indicator
on
the
mechanism
panel
will
point
to
the
word
"
OPERATE
"
.
-
•
•
FIG
.
17
.
Levering
-
In
Device
in
position
for
Rolling
into
Cell
able
crank
engages
another
shaft
in
the
right
front
corner
of
the
breaker
which
turns
the
arms
through
a
worm
gear
and
pinion
arrangement
.
Before
a
breaker
is
rolled
into
a
cell
,
the
arms
with
rollers
,
at
each
side
of
the
breaker
must
point
to
the
rear
and
slightly
downward
as
shown
in
Fig
.
17
.
The
arms
travel
193
degrees
and
assume
the
horizontal
position
shown
in
Fig
.
18
when
the
breaker
is
cranked
into
the
operating
position
in
the
cell
.
To
put
the
arms
in
the
position
shown
in
Fig
.
17
,
FIG
.
18
.
Levering
-
In
Device
with
Arms
in
position
taken
when
Breaker
is
in
Operating
Position
in
Cell
18
Courtesy of NationalSwitchgear.com

I
.
B
.
32
-
251
-
3
OPERATION
50
-
DH
-
150
&
-
250
AIR
CIRCUIT
BREAKERS
With
the
arms
to
the
rear
and
down
as
shown
in
Fig
.
17
,
the
breaker
is
ready
to
be
rolled
into
the
cell
as
far
as
the
test
position
.
The
rollers
on
the
arms
strike
vertical
angles
on
the
cell
wall
and
stop
the
breaker
at
the
test
position
.
If
the
breaker
is
to
be
operated
at
this
position
,
remove
the
crank
and
en
-
gage
the
secondary
contacts
in
the
manner
de
-
scribed
in
the
section
under
Secondary
Contacts
.
To
move
the
breaker
from
the
test
position
to
the
fully
engaged
operating
position
,
put
the
crank
on
the
shaft
,
push
in
and
rotate
to
engage
the
levering
-
in
coupling
,
and
crank
clockwise
.
The
torque
re
-
quired
will
increase
when
the
primary
contact
fingers
engage
the
stationary
contact
studs
in
the
cell
.
Continue
cranking
to
the
end
of
the
travel
where
the
interlock
will
again
fall
free
,
pushing
the
crank
back
out
.
Remove
the
crank
.
The
indicator
on
the
panel
will
again
point
to
the
word
"
OPERATE
1
'
.
To
remove
the
breaker
from
the
operating
posi
-
tion
,
first
check
that
the
breaker
is
open
.
The
lever
-
ing
-
in
device
cannot
be
engaged
unless
the
breaker
contacts
are
open
.
Put
the
crank
on
the
operating
shaft
,
push
in
and
rotate
to
engage
the
coupling
,
and
turn
counterclockwise
until
the
breaker
returns
to
the
test
position
.
Remove
the
crank
.
The
breaker
may
now
be
operated
at
the
test
position
or
rolled
out
of
the
cell
.
TEST
POSITION
The
breaker
may
be
rolled
into
the
metal
clad
cell
until
the
rollers
on
the
levering
-
in
device
stop
against
a
pair
of
vertical
angles
welded
into
the
cell
.
The
levering
-
in
device
is
not
operated
.
This
is
the
test
position
in
which
the
breaker
primary
contacts
are
separated
from
the
energized
contacts
in
the
cell
,
and
a
metal
shutter
is
closed
completely
isolat
-
ing
all
high
voltage
parts
from
the
breaker
.
The
secondary
contacts
may
be
engaged
and
the
breaker
operated
safely
for
test
purposes
without
the
arc
chutes
or
barrier
.
Caution
:
THE
BREAKER
SHOULD
NEVER
BE
MOVED
BEYOND
THE
TEST
POSITION
WITHOUT
THE
ARC
CHUTES
AND
BARRIER
IN
PLACE
.
LEVERING
-
IN
DEVICE
INTERLOCK
CAM
PUFFER
DIAPHRAGM
CLAMPING
RING
LEVERING
-
IN
DEVICE
GEAR
HOUSING
PUFFER
DIAPHRAGM
FRONT
PLATE
LEVERING
-
lh
DEVICE
ROLLER
INTERLOCK
PIN
GROUND
C
0
NTAC
1
SOLENOID
BACK
PLATE
SECONDARY
PLUG
;
ALIGNMENT
PINS
SECONDARY
CONTACT
PLUG
19
Courtesy of NationalSwitchgear.com

OPERATION
,
travel
,
all
the breaker
contacts
are
engaged
.
This
is
the
Operating
Position
.
Caution
:
WHEN
THE
BREAKER
IS
IN
THE
OPERATING
;
POSITION
IT
SHOULD
NEVER
BE
CLOSED
BY THE
MAINTENANCE
CLOS
-
ING
HANDLE
.
INTERLOCK
The interlock
on
the
DH
breakers
has
two
func
-
tions
to
perform
.
First
,
it
prevents
the
breaker
from
being
moved
from
the
test
to
the
operate
position
or
vice
versa
with the
contacts
closed
.
Second
,
if
the
breaker
is
in
some
intermediate
position
between
the
test
and
operate
positions
,
it
prevents
the
con
-
tacts
from
being
closed
.
This
interlocking
action is
accomplished
by
hav
-
ing
a
rod
,
operated
by
the
breaker
mechanism
,
and
a
pin
operated
by
the
levering
-
in
device
,
move
at
right
angles
to
each other
.
The
puffer
diaphragm
is
operated
by
two
puffer
rods
extending
through
the
puffer
casting
and
con
-
nected
to
the
trip
-
free
lever
of
the mechanism
.
The
right
hand rod also extends
beyond
the
rear
of
the
diaphragm
support
plate
and
is
directly
above
the
levering
-
in
gear
housing
,
and
at
right angles
to
the interlock
pin
.
See
Fig
.
19
.
When
the breaker
is
closed
,
this
puffer
rod
moves over
the interlock
pin
and
prevents
the latter
from
moving
upwards
.
This
prevents
the
engagement
of
the
split
coupling
on
the
levering
-
in
crank
shaft
through
the
action
of
a
bell
-
crank
casting
.
When
the breaker
is
open
,
the
puffer
rod
is
clear
of
the
interlock
pin
.
As
the
levering
-
in
crank
is
pushed
toward the
rear
to
engage
the
split
coupling
,
the
bell
crank
casting
lifts
the
interlock
pin
which
in
turn
will block
any
movement
of
the
puffer
rod
.
Thus
the
solenoid
operating
mechanism
cannot
move
from
the
open
position
.
As
the
crank
is
turned
,
a
cam
on
the
levering
-
in
shaft holds the interlock
pin
in
the raised
position
until
the
arms
are
at
either end
of
their
travel
.
At
this
time
the
spring
on
the interlock
pin
will
pull
the
pin
down and
separate
the
split
coupling
.
SECONDARY
CONTACTS
The
breaker
control
wiring
is
arranged
for
draw
-
out
disconnection
by
means
of
an
18
-
point
connector
plug arranged
to connect
to
a
mating
receptacle
mounted
in
rear
of
the cell
.
See
Fig
.
19
.
The
sec
-
ondary
connector
plug
is
mounted
on
a
moveable
bracket
on
the lower
left
hand
side
of
the
breaker
frame
.
This
permits
it
to
be
extended
to
the
rear
while
the
breaker
is
in
the
test
position
,
and
to
make
con
-
tact
with the
stationary
receptacle
so
that
the
control
circuits
are
completed
.
Sufficient
clearance
is
pro
-
vided
in
the
mounting
of
both
plug
and
receptacle
,
£
*
7
itCONDARY
CONTACTS
EXTENDED
FIG
.
21
.
Secondary
Contacts
extended
for
Completing
Control
Circuits
when
Breaker
is
in
Test
Postion
OPERATING
POSITION
The
breaker
may
be moved
from
the
test
to
the
operating
position
by
engaging
the
levering
-
in
de
-
vice
and
rotating
the
levering
-
in
crank
clockwise
.
As
the breaker
travels
beyond
the
Test
Position
,
the
metal
shutter
covering
the
high voltage
primary
con
-
tacts
will be
automatically
opened
by
the shutter
rollers
which
are
located
on
each
side
of
the
breaker
frame
at
the
rear
.
See
Fig
.
17
.
At
the end
of
the
20
Courtesy of NationalSwitchgear.com