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I.B. 8926-1
CURRENT TRANSFORMERS
When current transformers are used with overload re-
lays, the current through the overload relay heater is re-
lated to the motor full-load by the inverse of the current
transformer ratio.
WARNING: Do not ever remove heaters from Size 5
and larger starters to check unit operation. These start-
ers use current transformers to drop the current to the
range of the size 1 overload relay. Operation with heat-
ers removed will not interrupt voltage to the motor and
will generate dangerous voltages in the open secondary
of the current transformer.
MOTOR CIRCUIT PROTECTOR (HMCP)
AFTER INSTALLATION OF THE CONTROL CENTER,
EACH MCP MUST BE ADJUSTED TO ACTUAL MO-
TOR FULL-LOAD AMPERES (FLA) SO THAT IT WILL
TRIP AT ANY CURRENT WHICH EXCEEDS START-
ING INRUSH. This setting provides low-level fault pro-
tection. The first half-cycle inrush will vary with the mo-
tor characteristics. Motors with locked-rotor currents of
six times motor full-load amperes will usually require an
instantaneous magnetic setting of 7 to 11
times motor full-load amperes to prevent tripping when
starting.
A cam to accept a small narrow-blade electrician’s screw-
driver is near the lower left corner and around which are
eight lettered adjustment points, calibrated in trip am-
peres. See Figure 25. Adjustment should never exceed
13 times FLA which is in accordance with NEC require-
ments for magnetic-trip-only breakers. Adjustment
should be made as follows:
1.
Obtain FLA from motor nameplate.
2.
Multiply FLA by 13.
3.
Set the cam to the highest trip setting which does
not exceed the calculated figure of Item 2. This is
the maximum setting that should be used.
4.
Depress and turn the screwdriver adjustment coun-
ter-clockwise one setting at a time, until the breaker
trips in starting and then adjust upward one setting
position. This will insure that the circuit will open
instantly on any current above the motor inrush, usu-
ally 7 to 11 time FLA.
The PUSH-TO-TRIP button checks the tripping function
and is used to periodically exercise the operating mecha-
nism. The button is designed to be operated by using a
small screwdriver.
Freedom 21 00 MCC’s are supplied with Type HMCP
motor circuit protectors having an interrupting rating to
match the short-circuit withstand rating of the bus bar
system. For HMCP’s in 225,400 and 600 ampere frame
sizes, the magnetic-trip adjustment is set for each pole.
A three-pole HMCP has three trip settings to adjust.
Place all three poles at the same setting.
CURRENT LIMITERS FOR USE WITH TYPE HMCP
AND FD BREAKERS
The addition of the current limiter provides interrupting
capacity above the range handled by the HMCP in mo-
tor starters or by FD thermal-magnetic feeder breakers.
Each HMCP or FD breaker rated up to 150 amps has its
own current limiter to provide coordinated protection
against faults up to 1 00,000 amperes, rms symmetrical.
Built-in trip indicators in each phase immediately show
when a fault has blown the current limiter and tripped
the circuit breaker. This provides protection against sin-
gle phasing. After interrupting a fault, the current
limiter will require replacement. After the fault has
been cleared, the current limiter is replaced by the re-
moval of three screws. The breaker can then be reset to
provide for subsequent high overcurrent protection.
TYPE HMCP AND FD CIRCUIT BREAKERS WITH
TERMINAL END COVERS
Circuit breakers installed in units connected to 600 volt
distribution systems require a terminal end cap to be in-
stalled on the line side. Replace the terminal end cap
when replacing circuit breakers in such units.
Fig. 25 HMCP Magnetic Adjustment
Summary of Contents for Freedom 2100
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Page 32: ...Page 32 I B 8926 1 Part 11 PLAN VIEWS...
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