MCB tripping berofe RCD

Wearb

I came across a live to earth fault (damaged insulation on the live in a t+e cable) and the mcb alone tripped. This happened more than once. I replaced the cable and everything ok now. I was worried about it and wired a 60w bulb L to E in a 13A plug to test that circuit. RCD alone tripped this time, which makes me less worried.



Is that a normal sequence of events when there is a larger current, as in the first instance?

Conte..

I've seen the MCB trip or even both for a L-E short

Sometimes the RCD can be stuck too when the fault occurs, switching it on and off and pressing the test button frees it up which is maybe what happened there

adrian92

Wearb wrote: »

I came across a live to earth fault (damaged insulation on the live in a t+e cable) and the mcb alone tripped. This happened more than once. I replaced the cable and everything ok now. I was worried about it and wired a 60w bulb L to E in a 13A plug to test that circuit. RCD alone tripped this time, which makes me less worried.


Is that a normal sequence of events when there is a larger current, as in the first instance?

I think what you have done is ok, good.
The short circuit was rectified by your actions
Your test to simulate an earth fault confined that the RCD works.
All ok

Wearb

adrian92 wrote: »

I think what you have done is ok, good.
The short circuit was rectified by your actions
Your test to simulate an earth fault confined that the RCD works.
All ok

Thanks for reply. I just thought it strange that only the mcb tripped in the first instance.

adrian92

Wearb wrote: »

Thanks for reply. I just thought it strange that only the mcb tripped in the first instance.

Yes. Generally an earth fault occurs, with a fast response that the fault is cleared before the MCB looks after it , but not always.

It seems like a short circuit with no connections to earth.

Your measures are good, I think.

All good, in my view.

Nothing more needed

Conte..

The lamp would give you an idea if it's operational same as the test button

The RCD tester will check that it complies with regulations

Wouldn't be recommended to connect test loads across the protective conducter, might be alright if u had checked the fault loop impedance on the final circuit

Retro.

The danger with connecting a 60 watt lamp like that is that the RCD may not be working and the earth may be broken on the circuit

Anyone in contact with exposed metalwork would receive an electric shock