New CU. Please explain - Split Loads - RCBO/RCD's

[milllerr]

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I'm having a kitchen extension, and my old fuse board is being repositioned in part of the old kitchen.

I have agreed with my electrician to purchase the replacement board, but I have forgotten about exactly what configuration to buy. To save my embarrassment, could someone suggest what circuit configuration I should have in terms of circuit protection, i.e. RCD/MCB or RCCB/RCBO's. I believe RCBO's provide overcurrent protection, whereas RCD/RCCB's don't.

I have existing wring:

2 x lighting circuits
1 x ring main (which powers outside appliances such as pond pumps lawn mower)
Electric shower

New extension (or will have):

1 x ring main
1 x lighting
1 x cooker point
1 x cooker fan
1 x immersion
1 x boiler spur
1 x fire alarm

I quite like the idea of all the circuits having RCD protection, but I understand the idea of splitting the circuits so that light/cooker/immersion faults not turning off the power to the whole house. Is it best to have lights & ring mains on separate loads or what?

 

[Taylortwocities]

You just have to be embarrassed then.
The configuration, specification and layout of the board will be determined by the electrician. Go back and ask or you'll get the wrong thing(s).

He/she will be signing documents to say that the work they have done complies with BS7671. The work includes DESIGN, INSTALLATION and TEST.


In any case I can't believe that an decent electrician wouldn't be able to get a consumer unit at the same price as you could ( with trade discounts etc).

 

[mikhailfaradayski]

your embarassment will double after you get the wrong idea from here, buy a board which doesn't suit the job then have to go get another, probably at short notice.

I'm sure your spark wouldn't mind discussing it again, after all, its in his interest aswell that he has the right stuff

 

[Chri5]

I have existing wring:

2 x lighting circuits
1 x ring main (which powers outside appliances such as pond pumps lawn mower)
Electric shower

New extension (or will have):

1 x ring main
1 x lighting
1 x cooker point
1 x cooker fan
1 x immersion
1 x boiler spur
1 x fire alarm

Most will advocate RCBO's throughout as the absolute best set up. RCBO's all work on there own circuit, so if a circuit pops only that circuit dies.

With RCD's matched to a group of MCB's when the RCD trips all circuits on that rail fail.

An in between configuration would be an RCBO or suite of RCBO's for important circuits such as the fire alarm, security alarm (if installed) and the fridge / freezer (if you want the ultimate comfort / knowledge that the fridge / freezer won't be turned off due to another circuit on the RCD suite tripping).
Then the 2 x RCD rails are populated with general circuits.

The RCD rails should be populated to avoid mass failure of important circuits.

ie. Lights upstairs on 1 RCD rail, lights downstairs on 2nd RCD rail, same with ring circuits, fan them over both rails.

As for you intended outside ring, it's more common to have that as a radial circuit- 2.5mm TE at 20a or 4.0mm TE at 30a

If you go the way of 2 x RCD rails you also need to balance the loads, so don't have (say) 3 rings and cooker on 1 side and boiler and lights on the other (ie RCD1 3 x 30a + 1 x 40a = 130a , RCD2 3 x 6a + 1 x 20a = 38a).

 

[JohnD]

I have agreed with my electrician to purchase the replacement board, but I have forgotten about exactly what configuration to buy.

The electrician you mention often crops up on here. He seems to be the fully-qualified man who will do all the testing and issue certificates, but is always away on holiday so unable to answer questions or give advice. I've often wondered how he makes a living.

 

[milllerr]

Okay. I suppose I should have coughed I was an electrician in a former life, and if it was legal I would be doing all the donkey work installing all the new cabling and supplying the materials, including the new fuseboard and my Part P registered Electrician connecting up everything and testing and issuing the said certificate. However, it's not so ....... .

But RCBO's sound the best option, but quite expensive. Perhaps these for the ring mains & lights and an RCD and mcb's for the other circuits, hyperphectically that it is!

 

[stargazer]

I'm having a kitchen extension...

Given that you will need Building Regs approval for that, how are you going to avoid notifying the associated electrical work?
I'm no fan of the notification requirements of Part P, but can't see how you're going to get out of it.
You can still quite legally do the work yourself, which should not be a problem, especially if you were an electrician in a former life.
But you need to be up to speed with the current regs and notify the Council in advance.

 

[milllerr]

Yep, the planning permission/building regs approved long time since, and extension almost complete. I'm now looking at the CU hence my post.

I'm thinking of RCBO's for the ring mains & lighting, with everything else on MCB's off an 30ma RCD. Both controlled by a 100amp main switch.

Incidentally, the CU is fed by a 25mm 3core SWA, but I see that the MK main switch excepts up to 16mm. I seem to remember you could get lugs to terminate the cable wires to fit into the main switch terminals?

 

[ban-all-sheds]

Yep, the planning permission/building regs approved long time since

What did you say on your application would be the way you'd be complying with Part P?

 

[milllerr]

As I said previously, all the work will be carried out an tested and certified by my electrcian who is part P registered. This is how my building regs have been approved.

 

[davelx]

As I said previously, all the work will be carried out an tested and certified by my electrcian who is part P registered. This is how my building regs have been approved.

Then as TTC has already said, that electrician, who is going to take responsibility for the Design, Installation and Testing, is the person who has to decide what type of CU, CPDs, Circuits, cables runs, cables sizes etc etc etc are used. So ask him or her what you need.

 

[milllerr]

As I said previously, all the work will be carried out an tested and certified by my electrcian who is part P registered. This is how my building regs have been approved.

Then as TTC has already said, that electrician, who is going to take responsibility for the Design, Installation and Testing, is the person who has to decide what type of CU, CPDs, Circuits, cables runs, cables sizes etc etc etc are used. So ask him or her what you need.

This is a diy forum to get advice from your peers. Whilst I accept ultimately I can't certify this installation, I can certainly decide, if I so choose, what type of fuseboard and components it has. I may not decide to take the advice of my electrician, capable he is, but ask the advice of a wider audience, hence this thread.

I can't install gas boilers, but I can still decide if I want 'S' plan or 'Y' plan.

So I refer to my first post on this issue.

 

[LiamPope]

This isn't really a DIY forum - it's a club for pros where DIYers are often given short shrift (to be fair, in many cases, for their own good).

Have a look at this, and there are others similar from other manufacturers/organisations. It highlights some of the pertinent issues and considerations, and the various solutions available. See what takes your fancy. All RCBOs is the Rolls Royce of installations. Personally I've settled for a compromise of a twin RCD board with a few RCBOs on unprotected ways (currently cooker and smoke alarms).

Liam[/url]

 

[milllerr]

Many thanks Liam, most useful.

 

[davelx]

I can certainly decide, if I so choose, what type of fuseboard and components it has. I may not decide to take the advice of my electrician, capable he is, but ask the advice of a wider audience, hence this thread.

I can't install gas boilers, but I can still decide if I want 'S' plan or 'Y' plan.

So I refer to my first post on this issue.

Only if your electrician agrees to allow you to do so - he may well only agree to certify if you use the components and the design he specifies. His membership of the self-certification scheme explicitly prohibits him from signing off work that he has not either done himself, or has supervised someone working for his business to do.

BTW - I am a diyer, not a professional electrician.