Inline rcd

15 Mar 2006
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Tyne and Wear
United Kingdom

Currently got an inline 63a 30ma rcd to protect every circuit within very old cu

Ive currenty got hold of a split board half of it protected with rcd 30ma free of charge

If when i fit the new board if a circuit were to trip on the proteced side would it trip both the internal and the inline rcd or just one of them

Reason im changing the board as it is 14 way and ive currently only got a 4 way

Any help will be appreciated

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It would usually trip one of them.

Can you remove the in-line 30 mA RCD, and fit RCBOs on the unprotected ways?

It would be foolish to connect all the circuits to the protected side, and it would be foolish to have unprotected circuits if they are required to be protected.

What earthing arrangement do you have, e.g. TT, etc?

With respect, are you competent to do this work?

Make sure you fully research this project before even thinking about starting.
  • For a circuit to supply a given load, how would you go about deciding what cable and protective device to use? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)

  • Do you know which circuits can be ring finals and which cannot, and what the advantages and disadvantages of each are? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)

  • How do you calculate maximum demand and how can diversity be used?

  • Can you correctly identify all components and connections of a circuit by method of testing or otherwise? In doing so can you identify or recognise anything wrong or dangerous with the circuit? You cannot assume that what's currently installed is OK, and you need to check it before starting work.

  • Do you understand how the way in which cables are installed affects how much current they can carry? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)

  • Where cables need to be joined, how should this be done / not be done and in what circumstances are different methods acceptable?

  • Can you identify extraneous conductive parts, and do you know the requirements for main and supplementary bonding of them?

  • Which circuits should be RCD protected?

  • How do you propose to isolate your supply so that you can connect up your new CU?

  • Do you know what tests you would carry out on the installation - what sequence you'd do them in and at what point you would energise the installation, and for each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?

  • If you live in England or Wales, when you apply for Building Regulations approval what do you plan to say will be the way you'll comply with P1?
Hi and thanks for the reply

Yes i can remove the inline rcd but id obviously have to then replace with new tails

I am fairly competent but not qualified but fairly handy

Im not sure if i could change the mcb's for rcbos on the uprotected side not sure if they would be a straight swap / fit as this would be the best way

Its a hager board

I understand one of the rcds will trip just im thinking if the rcd were to trip in the cu first every time then at least id still have two proteced circuits but seperated if tat makes sense

Do you know if there is a replacement rcbo for hager cu's

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You can get Hager RCBOs to fit Hager consumer units.

Having a single 30 mA in front of a whole installation is asking for problems, as a fault will knock out the whole house.

You should get a good, qualified electrician to carry out this work.
It's more than likely that both RCDs would trip in the event of a fault in this case, assuming that they are both working within their required tolerances.

There's no Regulation to preclude the use of two or more RCDs together, provided that the tripping of either doesn't cause major inconvenience.

Never mind the current practice of using dual RCD boards, because there are many installations, such as this one, having but a single earth trip as a main switch - and there's no requirement for upgrading in spite of the obvious drawbacks.

The position here, if the O/P fits a split board, is that all circuits will still be protected by the main RCD, and some circuits will have the benefit of 'belt & braces' protection. So, in this respect, provided that he does the job properly, he'll end up with an installation no less safe than it was before - and that's the important consideration as far as Building Control should be concerned.

I'm not interested to pry into whether the O/P is 'registered', or 'legitimate', just so long as he does a reasonably safe job of it......


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