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Information and Instructions
Operation and Maintenance
Circuit Breaker Operation
With the mechanism latched and the
contacts
open ,
the
oper
-
ating handle will be in
the
OFF
position
.
Moving the handle
to
the ON position closes the contacts and establishes a circuit
through the breaker
.
Under overload or short circuit conditions
sufficient to automatically trip
or open
the breaker
,
the oper
-
ating handle moves
to
a position between ON and OFF To
relatch the circuit breaker after automatic operation
, move
the
operating handle
to
the
extreme
OFF position
. The circuit
breaker is now ready for reclosing
.
The
overcenter
toggle mechanism is trip free of the
operat
-
ing handle . The circuit breaker
,
therefore
,
cannot
be held
closed by means of the handle should a tripping condition
exist
.
After automatic operation
, the handle
assumes an inter
-
mediate position between ON and OFF , displaying a clear
indication of tripping
.
Molded Case Switch
A molded case switch is available in the MXD
6 ,
CMD 6 , NXD 6
and CND 6 type circuit breakers
. This device
employs the
same operating mechanism as the thermal magnetic and
magnetic only units
.
A
preset instantaneous function has been
factory installed to allow the switch to trip and protect
itself
against high fault conditions
. No overload or low
fault protec
-
tion is provided . This protection
must
be supplied by separate
overcurrent
devices . Catalog information is located on pages
44 and 46
.
Interrupting Ratings - Symmetrical RMS
Amperes ( kA
) Based on UL 489 Standards
Interrupting ratings of the MD and ND
-
Frame circuit breakers
are based on circuit and
test
conditions outlined in UL 489
.
RMS Symmetrical Amperes ( kA
)
lie
Am
®
ULA
.
I
.
R
.
Breaker
Type
Maintenance
Experience has shown that properly applied molded
case
cir
-
cuit breakers normally do
not
require maintenance . However
,
some industrial users may choose
to
establish
an
inspection
and maintenance procedure
to
be carried
out
on a regular
basis . For detailed information
,
consult applicable NEMA pub
-
lications or your local Siemens sales office
.
Volt
|
AC
(
50
-
60 Hz )
Volts AC
Volts DC
380 / 415
500
(
D
220 / 240
240 480 600
250
MD 6 , MXD 6 ,
ND 6 , NDX 6
50 ( 3 - P )
30 ( 2 - P ) 25 ( 3 - P ) 65 ( 3 - P )
65
50
25
HMD
6
,
HMXD 6
,
HND 6 , HNXD 6
100 ( 3 - P ) 65 ( 3 - P
)
30 ( 2
-
P ) 50 ( 3 - P )
100 65
50
CMD 6 , CND 6
(
D
30 ( 2 - P
) 50 ( 3
- P
) 200 ( 3
- P ) 100 ( 3 - P )
65
100
200
SPECIAL NOTE :
CMD 6 and CND 6 circuit
breakers are
not
UL listed as
interchangeable trips
—
DO NOT REMOVE TRIP UNIT
and replace
with another Removal
of trip
unit voids
UL
listing
.
®
Meets requirements of IEC 157
-
1 ( P 1 ) .
(
D
For 500 V dc applications the customer '
s
power supply and load must be
wired as shown ( Figure 1 )
.
( 3
)
CMD 6 and CND 6
type
circuit breakers are
current limiting at
240 V ac 480 V ac .
+
Q
Q
NOTE :
Present UL Standard 489 allows the
following toler
-
ances
for instantaneous adjustment
response
.
;
Thermal
-
Magnetic Breakers
Instantaneous
Adjustment
Low
:
±
25 %
±
20 %
instantaneous Only Breakers
:
H
Each Adjustment
+
30 %
1
High
Breaker
Outline
LOAD
Wiring Diagram
Figure 1
4
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