Household MCBs ( overload protectors)

[Nimalkad]

Recently I accidently found that one of the MBCs in our main board was not functioning. I had to replace two of them and test others by shorting the circuits. Is there a better method to test them?

[Neo]

You can use a voltage tester, a volt metre or a multi-metre to test this.

Warning: Safety first! You have to keep the electrical current on when you use the volt tester, so be cautious. Always wear rubber shoes or stand on a rubber mat when working on a control panel. Make sure the floor or earth underneath the panel is dry —not damp or wet. Water is an excellent conductor of electricity, and you don’t want to become part of the circuit. Wear safety goggles in case of flying sparks.

Now use following steps.

2. Get a voltage tester that’s rated for up to 500 volts
   These testers are available at most home improvement or electronic supply stores.
   
   
   
3. Remove the cover from the service panel
   You’ll see your circuit breakers (and they’re all clearly labelled, of course).
   Warning: Always take safety precautions: Wear rubber shoes when you work on a control panel and make sure the floor underneath the panel is dry.
4. Touch one prong to the terminal screw on the breaker and the other to the ground
   Warning: If you decide to use a voltage tester, don’t touch a bare wire or the neutral as you’re testing. If you do, you’re in for a bit of a jolt.
   
   
   
5. Check the glow light on the tester
   If the light doesn’t turn on, there’s no power and the breaker is faulty. You’ll need to replace it.

[Nimalkad]

Attn: Neo

What you have suggested will not test whether the tripping mechanism inside the MCB is faulty or not. Will it?

[Neo]

You are correct. There is no visible way to check it since the CBs are usually sealed. It seems the way you tested is the way to test them practically. It will be more safer if you could remove them from panel and test with some low voltage but I know this is not normally practical.
I faced similar problems with few Orange CBs few years ago but I think those are lot more improved now. However I replaced all with Hager and now I'm totally satisfied with the quality.

Lets see whether Magneto has some good ideas on this.

[Magneto]

Dear Friend ,

You can not test the tripping mechanism with out a variable current source. The systematic way of testing this
is using a Reostat and a ammeter. you have to conenct the Reostat , ammeter and MCB in series. Then by varing the
resistance of Reostat , you can change the current which is flowing throught the MCB. Then by using the ammeter , you can monitor whether MCB is switching off when it reach the rated current. Some times there could be small variation of this
switching point , but that could be neglected.

Regards,
Magneto