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 milli secondsand fractions of cycle(s) on the unit’s back-lit LCD screen (20 characters by 4 lines).MCCB-250 Current SourceThe MCCB-250 has 4 current-source outputs (5 A @ 120 Vac, 25 A @ 24Vac, 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 durationover-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 LCDscreen. When the MCCB-250 is used as a current source, the current-flowtime (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.
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