CU change. How many RCD's?

[D Skelton]

Hi people, I have a nice little consumer unit change to do in a couple of days. Quite a nice little job if you ask me but the funny thing is, it's in a flat and there are only three circuits. Lights, ring and cooker. What are your views on the type of CU I should put in? My thoughts are to use just a normal 4 way CU with main switch and just one RCD as I don't really see the point in using an 8 way dual RCD unit for such a small amount of circuits. Another thought I had was to use a 4 way board with each circuit protected by an RCBO, but this method puts the price up a bit.

The way I see it, if you can install a 12 way with 6 circuits protected by one RCD on each side then what would be the problem, if at all, with installing a 4 way with 3 circuits protected by one RCD? I mean, technically, no board complies with BS 7671 unless each circuit has its own RCBO but is this something that comes down to what is reasonable? By this, I mean is it reasonable to install an 8 way, dual RCD unit for just 3 circuits or would using just one RCD suffice?

Any thoughts?

 

[Spudnik]

RCBO's with main switch.

Size can be whatever will fit, but its best to have a couple of spare ways if possible.

 

[truckster]

Agree with Jason, it's a case of not losing everything if one cct faults out.

 

[Hawk81]

I would do the same as Jason.

 

[Sintra]

Definately go for the RCBO's

 

[D Skelton]

RCBO's it is then. Just for a little clarity though, what would be your reason for not using a single RCD?

it's a case of not losing everything if one cct faults out.

I agree, but like I said in my post earlier, how can you justify 6 circuits tripping out if one RCD faults out on a dual RDC 12 way unit but not be happy with only 3 circuits tripping out if they were the only circuits and protected by just one RCD that faults out?

 

[Paul.M]

Separation of circuits, if you have a 12 way split board with 2 lighting circuits you would put put d/s on one rcd and u/s lights on rcd2 that way the entire house isn't in darkness. With your problem of this flat only having the 3 circuits I would put the cooker and socket circuit on rcd1 and the lights on rcd2 that way the householder has got lights if the other trip, or for a bit more money use a rcbo for each circuit as above.

 

[truckster]

Convenience versus cost.

 

[Spoon]

We have a 16th edition cu, with just the 1 RCD. Its a bit of a pain when a bulb blows and sometimes trips the RCD.
I would go with RCBO's or Paul.m's idea.

 

[D Skelton]

Yeah, I'll go with RCBO's as well I think. It's just useful to sometimes get differing opinions on a topic but not many opinions seem to differ here

 

[Engineer54]

This is an absolute ''No Brainer'' What the hell are you arguing the ---- about?? You only have 3 circuits for god's sake. Not as if you had a 12 way CU, ....that's when you can argue about split RCDs etc...

 

[D Skelton]

Who are you ranting on about now?

 

[Engineer54]

Exactly what i said, ....It's a ''No Brainer''!!

 

[D Skelton]

Aren't you the clever one. Shame a friendly discussion had to be ruined by you, again!

 

[Paul.M]

Reg 314 Division of Installation. Every installation shall be divided into circuits, as necessary, to:- (i) avoid hazards and minimize inconvenience in the event of a fault. (iii) take account of danger that may arise from the failure of a single circuit such as lighting. (iv) reduce the possibility of unwanted tripping of RCD's......... It's only 3 circuits but we still have to take the above into account. Three rcbo's will satisfy all of the above in this case.