Siemens I-T-E Sensitrip MD Series Information And Instruction Manual Download

Page: 5 / 63

Information and Instructions

General

MD and ND-Frame Solid State Sensitrip style breakers of the
Sentron family, as shown on page 5, are for use in individual
enclosures, switchboards, and power distribution panel
boards. They are available both as 80% and 100% rated
devices and in three interruption ranges as shown in the table
below.

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Symmetrical RMS Amperes UL Interruption Ratings

Interruption

Rating

Type

240V AC

480V AC

600V AC

Standard

SMD6-SND6

65kA

50kA

25kA

High Rating

SHMD6-SHND6

100kA

65kA

50kA

Current Limiting

SCMD6-SCND6

200kA

100kA*

65kA*

*Not current limiting at 480 v AC and 600 v AC

SCMD6 and SCND6 type circuit breakers are designed to
meet the requirement of current limiting as outlined in the
National Electric Code, article 240-11 (1) and UL 489(2)
standards. SCMD6 and SCND6 type circuit breakers are
fuseless and therefore eliminate the requirement of locating
and replacing blown fuses should a high current fault occur.
The common trip feature of the circuit breaker is completely
retained so that all poles of the circuit breaker open when
caused to trip due to an overcurrent condition.

Pressure wire connectors, suitable for use with aluminum or
copper wire are available for all MD and ND-Frame circuit
breakers. Rear connection studs or plug-in connector(3)
assemblies are also available. The latter mounting arrange-
ment permits the removal of the circuit breaker from its leads
without physically coming in contact with either the line or
load terminals. UL listed special features such as a shunt trip,
auxiliary and alarm switches and undervoltage trip devices
are available for internal mounting. The installation and/or
removal of these devices is to be accomplished by qualified
personnel only. Information concerning special features can
be found on page 58.

The chart below illustrates the functions available in all
Sentron Solid State Sensitrip circuit breakers.

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Adjustments

Breaker Suffix Letters

ANT

ANGT

Long Time Adj.
Current Setting

✓

Adj.

Long Time Delay

✓

Adj.

Instantaneous

Setting

✓

Adj.

Short Time Pick Up

✓

Adj.

Short Time Delay

✓

Adj.

Short Time I²t

Pick Up

✓

Adj.

Ground Fault

Pick Up

✓

Adj.

Ground Fault Delay

✓

General Information

Circuit Breaker Operation

With the mechanism latched and the contacts open, the
operating handle will be in the OFF position. Moving the
handle to the ON position closes the contacts and establishes
a circuit through the circuit breaker. Under overload or short
circuit conditions sufficient to trip or open the breaker auto-
matically, the operating 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 operating
handle. The circuit breaker therefore, cannot be held closed
by means of the handle should a tripping condition exist. After
automatic operation, the handle will assume an intermediate
position between ON and OFF, thus displaying a clear
indication of tripping.

Maintenance

Experience has shown that properly applied molded case
circuit breakers normally do not require maintenance. How-
ever, 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 publications or your local Siemens sales office.

(1) National Electrical Code (240-11) A current limiting overcurrent protective device, which,
when interrupting currents in its current limiting range, will reduce the current flowing in the
faulted circuit to a magnitude substantially less than that obtainable in the same circuit, if the
device were replaced with a solid conductor having comparable impedance.

(2) Underwriters Laboratories (UL 489, Par 2.5) A circuit breaker that does not employ a fusible
element and that when operating within its current limiting range, limits the let-through 12t to
a value less than the I2t of a 1/2 cycle wave of the symmetrical prospective current.

(3) Plug-in assembly not available for ND-Frame