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MCCB-250 USER’S MANUAL
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1.0 INTRODUCTION
1.1 General Description and Features
The MCCB-250 is a programmable, high-current source designed specifically for testing molded-
case circuit breakers as well as thermal, magnetic, or solid-state overload motor-protection
relays.
MCCB-250 Timer
The MCCB-250’s built-in timer can test the time-delay characteristics of protection relays and
molded-case circuit breakers. Once the test is initiated, the current source and the timer are
automatically turned on at the next zero-crossing point of the AC. The timer stops when the
MCCB-250 input detects a change in the dry contact or voltage input, or detects the removal of
the test current. The test results are then displayed in milliseconds and fractions of a cycle(s) on
the unit’s back-lit LCD screen (20 characters by 4 lines).
MCCB-250 Current Source
The MCCB-250 has 4 current-source outputs (5 A @ 120 Vac, 25 A @ 24 Vac, 120 A @ 6 Vac,
250 A @ 3 Vac) that conduct the test current through the high-impedance load circuits. Each
current source can tolerate short-duration over-loads up to 4 times the rated current. This
feature is used for testing the instantaneous trip element of molded-case circuit breakers.
When using this feature, the selected test current is displayed on the LCD screen. When the
MCCB-250 is used as a current source, the current-flow time (the current-on period) is
displayed on the LCD screen.
External Current Input
The MCCB-250 also provides an external current input (0 – 10 A). Both internal and external
current source readings can be viewed at the same time.
1.2 Furnished Accessories
The MCCB-250 comes furnished with the following:
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Two 10-foot #4 AWG current cables with heavy-duty alligator clamps
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One 10-foot #10 AWG current cable
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Two 10-foot external current input cables with alligator clips
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Two 10-foot external timer input cables with alligator clips.
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One ground cable
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One power cord
