wire a single phase socket from a 3 phase rcd

dannynasir · Mar 17, 2012

Hi all
my first post hope someone can help me.
thanks in advance.
i want to wire a three pin socket (single phase) from a 3 phase rcd which has 3 lives a neutral and earth.
can i take one of the lives, neutral and earth to a 13A fused spur and then to a 3 pin socket.
all help much appreciated.
thank you
danny

Tris Zanker · Mar 17, 2012

I've got a feeling that the RCD will just trip if you do that , i would think that you'll need a blanced load on each Phase but i'm really not sure.

micknew · Mar 17, 2012

It would't trip, think about a 3 phase RCD feeding a mixed load 3 phase cb board.

Tris Zanker · Mar 17, 2012

Ye i didnt even think about that, it would be fine then .

dannynasir · Mar 17, 2012

thanks for your replie's peeps.
reason i ask is that i did one before about 6 months ago as the 3 phase rcd feeds a sunbed and i fitted a 13A fused spur and then to a 3 pin socket to run a vibrating exercise plate, they have both been working fine, they are never on together only one at any one time, now i am fitting another one to a different sunbed and i thought better make sure it's safe to do it this way.
so you lot think i am okay to do this?
regards

mogga · Mar 17, 2012

single phase from a 3phase RCD,MCB is a NONO FFS your not talking about a distribution circuit but a final circuit so the answer to your question is NO
Although you will probably do it as you sound like the sunbed shop owner and would rather DIY than Do It Correctly WHO is certifying your work? Have you informed your insurance company of this work? have your local authority liscencing board been told of your expansion and unsafe practices?

londonlec · Mar 17, 2012

mogga said:
single phase from a 3phase RCD,MCB is a NONO FFS your not talking about a distribution circuit but a final circuit so the answer to your question is NO
Although you will probably do it as you sound like the sunbed shop owner and would rather DIY than Do It Correctly WHO is certifying your work? Have you informed your insurance company of this work? have your local authority liscencing board been told of your expansion and unsafe practices?

Have I missed something?!

A single phase load off a three phase DB and RCD?... and?!

dannynasir · Mar 17, 2012

getting mixed replies!!!!!!!!!!!!!
come on peeps please can someone tell me if it's safe
thanks

RISElectrical · Mar 17, 2012

3 phase distribution board with a single phase MCB supplying a final circuit is fine. So long as ratings etc are correct.

If you mean a 3 phase (TP) MCB supplying a single phase final circuit then no that's not ok.

I don't think your explanation of what you intend to do is worded very well. If you have to ask the question then are you sure your competent or confident enough to do the work? No offence intended, just making a point.

Engineer54 · Mar 18, 2012

i want to wire a three pin socket (single phase) from a 3 phase rcd which has 3 lives a neutral and earth.

I don't think i've ever seen a 3 phase 4 pole RCD that has an earth connection!!! lol!!

spark 68 · Mar 18, 2012

micknew said:
It would't trip, think about a 3 phase RCD feeding a mixed load 3 phase cb board.

Sorry, but I think it would trip as the core would be out of balance If you were to pull a single phase from a 3 or 4 pole RCD.

You don't normally have an up front RCD on boards like this for this reason, unless all phases are equally balanced, rather the RCD's or RCBO's feeding the individual final circuits, Either TP,TP+N or SP where required.

ringer · Mar 18, 2012

Why (unless a fault is occurring) would it trip? The RCD will sum the three incoming lines and compare it to the outgoing neutral. Same principle as a SP RCD really.

There are people on this thread who are saying that unless a 3PH system is balanced then the RCD will trip. How many of you have ever seen a perfectly balanced 3PH system? I'm pretty sure I haven't.

rich.250 · Mar 18, 2012

spark 68 said:
You don't normally have an up front RCD on boards like this for this reason, unless all phases are equally balanced, rather the RCD's or RCBO's feeding the individual final circuits, Either TP,TP+N or SP where required.

Why would it trip. In a TT system you would have a 4pole Rcd upfront in a seperate enclosure. Does that trip???
No.
The Rcd will only do what it is designed too. I detect an imbalance between line and neutral.
And thus must be a leakage.

The reason they are avoided upfront is inconvenience!! Not that they will trip.
Also not all circuits in a 3phase system generally need Rcd protection.

rich.250 · Mar 18, 2012

So if the circuit is fed of an adequate cb for cable sizing and correction factors are applied I don't see the issue. Apart from reg 314.1 and 2 saying division for circuits to avoid inconvenience.

mogga · Mar 18, 2012

OP is talking about using 3ph rcd for final single ph circuit NOT via a BD from the way Im reading

wire a single phase socket from a 3 phase rcd

dannynasir

Tris Zanker

micknew

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Tris Zanker

dannynasir

mogga

londonlec

dannynasir

RISElectrical

Engineer54

spark 68

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ringer

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rich.250

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rich.250

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mogga

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