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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
    The wall cannot be altered. This is the first thing I have asked.

    It is not on the table as an option.

    Unfortunately.

    The feeder is like 40m in lenght running in a cable basket and then drops into a wall partition for 30cm to meet with the back of the CU.

    The problem is that when I designed it I considered only the 40 meters on the cable basket however I did not realise that for the last part it needs to go into the wall partition.

    An now I MUST use an RCD and I am looking if I can use a time delay one.

    Alternatively, the easy solution is to take out the RCD incomer of the CU and use a regular 30mA RCD int he beginning of the feeder.

    Cheers
Reply
  • 0
    The wall cannot be altered. This is the first thing I have asked.

    It is not on the table as an option.

    Unfortunately.

    The feeder is like 40m in lenght running in a cable basket and then drops into a wall partition for 30cm to meet with the back of the CU.

    The problem is that when I designed it I considered only the 40 meters on the cable basket however I did not realise that for the last part it needs to go into the wall partition.

    An now I MUST use an RCD and I am looking if I can use a time delay one.

    Alternatively, the easy solution is to take out the RCD incomer of the CU and use a regular 30mA RCD int he beginning of the feeder.

    Cheers
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