MCB tripping - why?

[nafuk]

Hi, the MCB on my split circuit consumer unit is tripping sporadically, sometimes when nothing is connected to the downstairs socket circuit. The MCB protects the RCD protected circuits (upstairs and downstairs sockets, cooker, hot tank, kitchen sockets). The hot tank and cooker circuits are turned off at the rcd and are not connected used/connected yet.The light (non-RCD'd) circuits stay on when the RCD trips.

Please can someone tell me what causes an MCB to trip, other than overcurrent, and not trip an RCD, and hopefully some possible things to check in order to locate the fault.

This 'may be' heating associated but does happen when the heating is off and the boiler is off i.e. could it be associated with hot pipes near a cable?

Many thanks.

[John Rumm]

I am guessing that you have transposed the terms RCD and MCB here, and what you actually have is a nuisance RCD trip. You will need to be methodical to track down the cause of this. Some advice is given in the nuisance trip section of this article:

[Graham.]

you actually have is a nuisance RCD trip. You will

the nuisance trip section of this article:

I am confused by his post too. If the individual circuits are protected by RCBOs rather than RCDs it begins to make more sense

[george [dicegeorge]]

you actually have is a nuisance RCD trip. You will

in the nuisance trip section of this article:

i think an rcd/rcbo can trip even if the circuit is turned off, if its a singlepole switch and only cutting power to the live wire, because a leak from the neutral to earth would trip the rcd as neutral and live would then be unbalanced.

so maybe disconnect some neuatralsl and see if that stops it.

[g]

[nafuk]

Sorry, I do have my MCB and RCD's mixed up.

Thank you for the info and pointers..

[Rednadnerb]

I recently had the same problem and got some excellent advice from this forum, see my post:

fixed.

Brendan

[myfuturenrk]

presently there is an C6 MCB can I replace it to 16 to resolve this problem

[Dave Liquorice]

Assuming that you really mean MCB then you need to find the reason for the instant overload.

[DerbyBorn]

What is your "water heating coil"? What checks have you done on it?

[Martin Brown]

Did it work in the past? Why is it tripping? Have you checked earth leakage?

[charles]

What are you doing with a water heating coil on a lighting circuit?

[Brian Gaff]

Kind of lacking in information to make such a decision unless you are of the kill or cure type. IE insert six inch nail and see what goes bang. Brian

[Robin]

Is this a free-standing heating coil such as ?

Are you in the UK or are you elsewhere - eg in India?

[Dave Plowman (News)]

Sounds like you need to get a pro in.

[John Rumm]

What kind of water heating coil are we talking about?

(A 6A MCB sounds rather low for most heating circuits - that would limit the heater power to about 1300W - however you can only substitute a higher trip current MCB if the cable size is large enough to remain protected)

[Bob Minchin]

One has to wonder why a type C is being used instead of the more usual type B for domestic circuits?

[Harry Bloomfield]

[e-mail] expressed precisely :

The sent from IP seems it might be Shertallai, Kerala, in India.

[Roger Hayter]

If it is a two or three kilowatt heater the result is unsurprising.

[Dave Plowman (News)]

Not that uncommon on lighting circuits with lots of LV stuff - especially when transformer fed.

[John Rumm]

I normally spec a type C for lighting circuits since it makes them less likely to trip on a filament lamp failure IME. Not really any downside in doing so as long as you make sure the ELI at the furthest part of the circuit is less than 3.64 Ohms[1].

[1]