Wickes two mcb RCD CU

I'm not familiar with that particular CU, but is sounds like a perfectly standard layout.

Well, no. From the description given above the incoming supply must go to the top RCD terminals because the bottom ones would appear to be the outgoing feeds to the 'live' (strictly, phase) busbar and to the neutral bar.

The two outgoing final circuits are taken from the top terminal of each MCB and the neutral bar. The earth bar is common to everything: the incoming earth (or local earth rod, if it's a separately earthed TT installation), the outgoing circuit earths and any main bonding conductors.

HTH - but if not, please provide a photo somewhere.

Thanks for the reply.

The small link is for the live and is called a bus bar. It is three lugs that slot into the live terminals of all three switches of RCD and two mcbs.

Yes, that appears logical. Live in top of RCD and lives out to mcbs via a small bus bar. It is the neutral wire from the neutral terminal that goes directly to the output terminal of the RCD, which has thrown me. The neutral is not switched through the RCD, although a terminal is there to switch it on the RCD. I assess that this is to make the RCD work not being familiar of operation.

If an mcb has a switching mechanism for both live and neutral (two terminals on the input and output) can these be used and not take the neutrals from the common neutral terminal strip? It must be safer to isolate both live and neutral when the mcbs are off.

Sorry, I can't get a picture of it just yet. They are on the shelves at Wickes. ;-) Once again thanks.

Yes, and the Neutral bus bar will be elsewhere in the CU and fed via a link cable or rod from the other terminal on the *bottom* of the RCD.

The Neutral of the supply is connected to the *top* of the RCD - next to the Phase from the supply. The outputs from the RCD are at the bottom, one to the phase bus bar (metal thing with lugs), the other (typically [1]) via a cable to a neutral bus bar - multiway cable terminal with screw downs.

No - the neutral *is* switched via the RCD. Both phase and netural must pass out and return via the RCD in order for it to operate correctly.

They don't. MCBs in this type of CU are usually single pole and switch the phase only.

Thanks. I get it now. The CU has two terminal strips, earth and neutral. The live and neutral come in and connect to the "top" of the RCD switch. The earth goes straight to the earth terminal. The output of the RCD switch has the live going to the two mcbs via a amll bus bar link, the neutral to the neutral terminal strip. When the RCD is off there is no supply to the live bus bar or neutral terminal strip, cutting out the lives and neutrals to all circuits. This makes sense. The mcbs have the live from the output of the mcb and take take the neutral from the common neutral terminal trip.

Spot on.

For completeness.....

In a larger CU with the possibility of configuring a so-called "split" arrangement, there are normally two neutral bars connected initially with a link.

The supply phase and neutral normally go into an incomer switch (non-RCD if it isn't a TT system). The phase on the load side goes to a bus bar which hooks together MCBs that are not being connected via an RCD. The neutral on the load side of the incomer is connected to the neutral bus bar.

If there is to be no RCD at all (unlikely these days), MCBs are fitted all the way along and the link between the neutral bus bars stays in place.

If there is an RCD, then the phase bus bar is cut appropriately and the RCD fitted. The RCD takes its supply from the load terminals of the incoming switch. The load phase connection of the RCD goes to a second bus bar to feed downstream RCDs and then there is a neutral connection from the load neutral of the RCD to the second neutral bus bar. *Very Important*. The link between the two neutral bus bars must be removed.

Just the same as any CU. The master switch - or RCD - is double pole. MCBs

- or even fuses - are only on the line. Split load CUs are more confusing as you need two neutral busses - one for the RCD protected side and one for the non RCD one.