How to wire a standalone RCCB (RCD)

absoft · 3 Nov 2007

Hi, I am wiring a 40A standalone RCCB (in its own housing) after the fuse box. It has two terminals top and bottom; none of which have any markings on them. I assume I continue live on the same side top and bottom and similarly with neutral, but does it matter which side live and neutral are? Also does it matter whether the top is connected to the fusebox and the bottom to the ring or whether its the other way round?

Similarly for a standalone MCB with two terminals, does it matter which way the current flows? i.e. from top to bottom or bottom to top or will either do?

JohnD · 3 Nov 2007

RCD will work either way because it just compares current flowing through one side with curent flowing through the other. However, if it has a thin white functional earth wire, it must be installed as indicated by the manufacturer. In this case if it is not marked, ask them.

Usual is supply top, load bottom for an RCD or a main switch

Supply bottom, load top for an MCB

follow any terminal markings (e.g. L1, L2, N1, N2)

If you say the make and model someone may know.

What are you doing with it? Bit concerned you seem to be pushing the envelope of your knowledge.

absoft · 4 Nov 2007

Thanks for the info John. The unit is made by Hager (french). I am protecting each ring with its own RCCB by inserting the RCCB between the fuse box and the ring main, running 30A wire between the fuse box and RCCB of course (only a short length). I did two a long time ago which have worked fine but just forgotten the details.
When you say for an RCCB the power usually comes in at the top and out the bottom and for an MCB its the other way round; are you saying there is only one correct direction for the current and that if they were connected differently it would be wrong or just that that is the convention but it doesn't really matter?

kai · 4 Nov 2007

There is normally a wiring diagram printed on the side of the RCD, which should guide you, normally the Phase and Neutral enter and leave the RCD on the Same Side respectively, and the Earthing conductors are connected to the earth terminal inside the din-box enclosure etc.

My RCD states that it does not matter which side is Phase or Neutral, but ideally should follow the same convention as any other main switches or RCD's on the same installation for consistency if possible.

securespark · 4 Nov 2007

I use Hager & many other brands of RCD all the time. As John says, unless they have an earth connection or are specifically marked, you can wire them any way round, as long as the neutrals & lives are in line with each other.

JohnD · 5 Nov 2007

absoft said:
I am protecting each ring with its own RCCB by inserting the RCCB between the fuse box and the ring main

should have bought RCBOs

GaryMo · 5 Nov 2007

JohnD said:
absoft said:

I am protecting each ring with its own RCCB by inserting the RCCB between the fuse box and the ring main

Click to expand...

should have bought RCBOs

Which would have been useless if he has a 'fuse box' (as he mentions).
He does talk about MCB's but mentions 'standalone' use for some reason.

Maybe the OP can give a little more detail?

absoft · 5 Nov 2007

This is a great site; thanks for the help.
Yes I have a fuse box still so the combined MCB/RCCB is not an option without a new consumer unit.
I just wondered whether the MCB's were 'reversible' in terms of which terminal is on the supply side and which on the load. (I have in mind to also add MCB/RCCB protection to the cooker circuit via one of those 'garage' consumer units with a single RCCB and a single MCB; I would replace the 40A MCB with a 30A one though)

GaryMo · 5 Nov 2007

It doesn't matter if you feed the top or bottom of an MCB, either will work fine.

JohnD · 5 Nov 2007

Hi, Gary. I have led a very sheltered life and have never seen a Hager Fusebox with rewirable fuses.

I have seen lots of Wylex, some MEM, some GEC and various others including ones made of wood or cast iron.

absoft, a picture of this Fusebox or consumer unit would be very helpful to save us having to imagine what you've got.
//www.diynot.com/forums/viewtopic.php?t=99672

GaryMo · 5 Nov 2007

JohnD said:
Hi, Gary. I have led a very sheltered life and have never seen a Hager Fusebox with rewirable fuses.

Actually John, now you mention it, neither have I

absoft · 6 Nov 2007

The fuse box is a MEM; I said the RCCB was a Hager, totally seperate. Sorry for any confusion.

JohnD · 6 Nov 2007

picture! picture!

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How to wire a standalone RCCB (RCD)

kai

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