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Time delay RCD - BS7671

Apostolos
Good morning.

We have a feeder to a consumer unit that for the last 30cm of its route it goes into a metal stud wall partition.

This was not caught early so that we could use an earthed metal conduit for this length and the walls are all up. Done and dusted.

This practically means that the feeder needs an RCD protection in the beginning.

End of story since we cannot interfere with the wall now.

The problem is that the CU has an 30mA RCD incomer itself.

So the RCD we are going to install upstream will be in series with the RCD incomer of the CU.

Does BS7671 accept a time delay 30mA RCD for the feeder that goes within the wall partition?

If it would I could still have some kind of "discrimination" with the RCD downstream in the CU.

I have been looking through BS7671 to find a respective regulation but I could not find something.

My gut says that its unlikely that I can use a time delay RCD but I cannot substansiate this with a regulation.

Any help is more than welcome!

Cheers

Parents
  • 0
    What size of supply are we talking about? 100Amp three phase or 1000Amp 3 phase? and what size and type of cables are in use? (This will let us know how easy or hard that last little bit may be to remove from the wall and DB without damaging the wall)


    In basket and not SWA - have you used the HORNY 7 cable? (H07RNF) in which case it should be fairly easy to withdraw?


    If you cant withdraw the last 30cm of run, Is the aesthetics particularly important to where the DB is and do you have the space to fit an isolator such as  Contactum - 400 Amp TP&N Switchfuse - Contactum or a suitably rated "connector block" in a metal clad box in order to lengthen the bit to get down to the board in metal trunking that runs down the side of the DB. I think locating the RCD in the feeder pillar will cause future headache galore. If the supply is small enough you could even use henley blocks.
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  • 0
    What size of supply are we talking about? 100Amp three phase or 1000Amp 3 phase? and what size and type of cables are in use? (This will let us know how easy or hard that last little bit may be to remove from the wall and DB without damaging the wall)


    In basket and not SWA - have you used the HORNY 7 cable? (H07RNF) in which case it should be fairly easy to withdraw?


    If you cant withdraw the last 30cm of run, Is the aesthetics particularly important to where the DB is and do you have the space to fit an isolator such as  Contactum - 400 Amp TP&N Switchfuse - Contactum or a suitably rated "connector block" in a metal clad box in order to lengthen the bit to get down to the board in metal trunking that runs down the side of the DB. I think locating the RCD in the feeder pillar will cause future headache galore. If the supply is small enough you could even use henley blocks.
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