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Is My MCB Not Working Properly?
Marginal Overcurrents:
At mild or marginal over currents it's probably working just fine. The latitude for tripping is pretty wide. See the table below:
Table
Interpretation of Table:
Say you have a 16 amp breaker. Assume a load of 18 amps.
The MCB should either NEVER trip, or trip within 1 hour, so the breaker may function day in day out with no spurious tripping.
If the breaker 'sees' 20 amps, it should trip within 2.5 minutes to 1 hour.
Most electricians have no time or the capacity to thoroughly test the equipment, so if an over-current is detected then breakers are simply replaced to maintain safety standards.
Before a miniature circuit breaker is condemned, check if the MCB is a B, C or D type and compare the current vs tripping curve accordingly.
Click here for a handy link to a MCB data sheet and graphs.
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