Routine maintenace tests for circuit breaker

Circuit breaker is the important protection device for our application and electrical power supply system.It can save our equipment or machinery from damage from over current or overload matter.It also can save personal life who involve directly or indirectly with electrical application from electric shock.

How we can know the actual condition and reliability for our circuit breaker? Normally we must perform the routine maintenance tests to determine out circuit breakers are able to perform their basic circuit protective functions and in good condition.

This time i want share information about routine maintenance tests for circuit breaker.Below i listed 5 types of tests to determine and assuring that the circuit breakers are functionally.Please be caution before perform the tests are to be made only on breakers and equipment that are on de-energized mode ( power supply OFF ).

Routine maintenance tests

1) Insulation resistance test.

This test is a common practice to check the condition of circuit breaker.I already explain detail in my last post about insulation resistance tester.To perform this test we must used a mega ohm meter or insulation tester meter to check insulation value between phases of opposite polarity and from current-carrying parts of the circuit breaker to ground.

We should test the insulation between the line and load terminals with the circuit breaker in the open position.The load should be disconnected from the circuit breaker under insulation resistance tests.It is to prevent a test mesurements from also showing resistance of the circuit load.

Resistance values below 1 mega ohm we can consider the breaker is defect and  should be inspected for any possibility failure at contact area.For easy we change a new circuit breaker with high quality and durability.

2) Millivolt drop test

A millivolt drop test can disclose several abnormal conditions inside a breaker such as eroded contacts, contaminated contacts, or loose internal connections.

The millivolt drop test should be made at a nominal direct-current voltage at 50 amperes or 100 amperes for large breakers, and at or below rating for smaller breakers.

3) Connections test.

To perform this test we can use a multimeter and select continuity ohm reading. The connections to the circuit breaker should be inspected to determine that a good joint is present and that overheating is not occurring.

Overheating is a main cause for cable and circuit breaker default.If overheating is indicated by discoloration or signs of arcing, the connections should be removed and the connecting surfaces cleaned.

4) Overload tripping test.

This is a important test to ensure a circuit breaker tripping when overload happend.To test for the overload tripping components of the circuit breaker can be verified by applying 300 % of the breaker rated continuous current to each pole. The test must include with affected by ambient conditions and test conditions.

5) Mechanical operation.

The mechanical operation test is important too to make sure circuit breaker mechanism not stuck or have a problem to activated when overload or over current happened.

Circuit breaker mechanism must be in good condition and if we found any abnormality during mechanical test,we must to checked the condition and replaced it if the defect is too critical and cannot fix anymore.


  1. haitham hashim says

    Very important issues in the work of maintenance

  2. Sampath de silva says

    Very important facts

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