Layout for a simple consumer unit for a flat -

[Algy]

My daughter has just bought the downstairs half of a old corner shop converted to a flat 23 years ago. The wiring was done at the same time and contains a fuse type CU.

She is getting the wiring checked and the CU replaced with a MCB type. I mentioned to the potential electrician that I had heard that a split CU with RCD protected MCB on one side and just MCBs on the other (for those possible nuisance tripping sources) was best, however given it is a small flat, it only has 3 fuses (lights/sockets/cooker).

He suggested have a 6 + 6 unit with RCd + lights + sockets on one side and strangely another RCD + cooker on other.

Is this sensible? There will be a lot of empty slots in it of course, but I guess a 6 + 6 box is the smallest available? Do we need 2 RCDs? Should we just have all on one RCD? Or ..... ?

Advice on a layout for this small unit is appreciated.

I saw a forum discussion on whether a cooker should be on an RCD (tripping issues) and there was no real agreement.

Thanks.

 

[Lectrician]

I would fit a 4 or 6 way board, with a normal 100amp incomer, and fit an rcbo for the socket circuit, and normal MCB's for the cooker and lights.

Also, as a matter of course, the main equipotential bonding, and the supplymentary equipotential bonding should be upgraded.

 

[ebee]

RCD protection is a good idea electrically because it gives additional protection. However if one is fitted as a "main switch" it would mean loss of all circuits protected by it in the event of an earth fault (socket circuit earth fault means losing lights in dark making you electrically safe but break your neck by falling).
Socket circuits usually must be RCD protected and if the cooker control has a socket then yes that too.
Cookers (even brand new ones) tend to be electrically leaky anyway.
One consideration in a TN system is Plain switch and RCBO (RCD & MCB combined in one "breaker" )for each circuit, thereby affording both Earth fault & overcurrent protection for each circuit.
If circuits are split sensibly than any loss via a fault will only be to a small proprtion of the whole system.
Ideally if all points were on a seperate circuit each with RCBO`s then goody, but it will cost a fortune, the switchgear would fill a room and I`ve never met anyone who`s seen such a system.
Unless T Blar & Two Jags have one in their bunkers.

 

[Lectrician]

The cooker control unit socket, and indeed, any other socket will only require RCD Protection "if it can reasonably be expected to supply portable equipment outdoors" (your lawn mower, hover etc).

Not every socket requires protecting, although most sparks worth their salt will protect all sockets, the CCU being a possible exception - especially as cookers are inherently leaky!

 

[ebee]

The cooker control unit socket, and indeed, any other socket will only require RCD Protection "if it can reasonably be expected to supply portable equipment outdoors" (your lawn mower, hover etc).

Not every socket requires protecting, although most sparks worth their salt will protect all sockets, the CCU being a possible exception - especially as cookers are inherently leaky!

Agreed, but what is reasonable and what is not. In my view all sockets normally fall into this classification even bedroom ones (we all see extensions thrown thru bedroom windows for power tools). Exception perhaps 13 storeys up in a block of flats.

 

[Lectrician]

It's the good old regs wording again......

It would depend on install to install really.

In a block of flats we have done recently, the NIC where happy with the communal area sockets being fed via an RCD - the flats actually did have RCD protection to sockets, but we were told it was not necessary.

Similarly, in a large office full of computers, you wont want an RCD in site...........we provided a socket with integral RCD adjacent the two fire exits. That was also satisfactory in the eyes of the NIC.

In a domestic dwelling, all sparks, including me will usually RCD protect all sockets. It's just the cooker one that can be spurious. I tend to fit 45amp DP switches rather than a CCU anyway

I know the NIC dont make the rules, but it does give you some confindence.

 

[securespark]

He suggested have a 6 + 6 unit with RCd + lights + sockets on one side and strangely another RCD + cooker on other.

Is it an overhead supply? Is one of the RCD's a TD version?

 

[ebee]

It's the good old regs wording again......

It would depend on install to install really.

In a block of flats we have done recently, the NIC where happy with the communal area sockets being fed via an RCD - the flats actually did have RCD protection to sockets, but we were told it was not necessary.

Similarly, in a large office full of computers, you wont want an RCD in site...........we provided a socket with integral RCD adjacent the two fire exits. That was also satisfactory in the eyes of the NIC.

In a domestic dwelling, all sparks, including me will usually RCD protect all sockets. It's just the cooker one that can be spurious. I tend to fit 45amp DP switches rather than a CCU anyway

I know the NIC dont make the rules, but it does give you some confindence.

Yes again I agree, I almost never fit a CCU but a 45A DP instead for that very reason plus, in my view it`s a thro back to the days when we did not have enough sockets, it`s meant for occasional use of a kettle, but how often do folk run washer or dryer from it. So no socket on cooker circuit removes the temptation.