Dual Split Consumer unit and Fire Alarms

[switch33859]

I am about to have my house rewired to 17th edition and have bought a dual RCB consumer unit. The feeds for the 2 RCDs from the main switch are already in place (bought with RCDs and MCBs all in).

I have read that the fire alarms should be on an independant circuit and not protected by an RCD.

Problem I have is im unsure if this cu I have bought (Wylex NH Range Dual RCD Split Load 10 way), has space for an RCBO.

So the questions I have are:

1) Can the fire alarm be run from an RCD protected circuit or is this a complete no-no?

2) There are 4 cables (2 neutral, 2 live) from main switch to 2 RCDs - it is possible to run additional cable from here (main switch) direct to single RCBO so not protected by RCD (what size would be needed - its looking pretty crowded at the base of the main switch)?

3) Do i need to take this cu back to shop and buy something different?

I have struck a deal with my sparky that i will do a lot of the donkey work - lifting floorboards, buying materials a) to reduce costs and b) he is extremely busy so it trying to squeeze me in - i have known him for years and trust him so will happily wait a bit but i don't want him coming if i don't have everything in place for when he arrives. I would ring him but the lucky get is on holiday in France..

Your help would be greatly appreciated.

 

[ban-all-sheds]

You must ask all these questions of your electrician, he is the only one allowed to make design decisions, as he will have to sign a declaration to say that he did all the work.

There's no problem with you doing labouring tasks, if you think about it unqualified apprentices work under the supervision and direction of someone qualified, but he will be held responsible for the design, so he must be the one to do it.

If you can't phone him then you'll just have to wait until he gets back from holiday.

 

[switch33859]

I don't want to do these works - i just want to have all the kit for when he comes back.

 

[ban-all-sheds]

Please read what I wrote again - he is the only person allowed to make design decisions and he must be the one to specify what you should buy.

 

[switch33859]

By trade i'm a Civil Engineer with over 10 years in the game. I am often asked by people for my expertise and advice (from friends, family, collegues and other Civils folk - outside my normal working requirements/responsibilities).

My answer is never i can't answer that you must speak to your builder/designer. I offer impartial advice as best I can because i feel this is part of my duty of being a professional. I often say though - 'you will need your designer to do the calcs for that, or your builder needs to be happy with that', but at least they have a suggestion(s) they can put forward, ideas that they have discussed and understand a little more than before.

Like everything in the building game there is always more than one way of doing things. I am simply asking for a solution that would meet current regulations based on all the information I have given so I may buy the materials and do some works in readiness for my Sparky coming to do the work.

When he arrives I would like to say 'this is what i thought for the fire alarms'. Im sure if it met regs he will be happy to install and if it doesn't im also sure he wont.

Just seems better than him coming and us wasting half a day driving to
get more kit.

Advice thats all im looking for.

 

[londonboy]

Take it back and buy one of these:

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_17_Consumer_Units/index.html

The alarm doesn't need to be rcd protected, but if you (or your spark) insists then at least with that board you could fit an RCBO.

Looking at those prices id buy the larger board (for expansion/extensions etc)

Hope that answers your question.

 

[Pants7478512]

They can be run from either a dedicated circuit from the distribution board or from a local regularly used lighting circuit.

If you are going to supply from a lighting circuit there should be some way to isolate the supply to the alarms without affecting the lighting.

They can be RCD protected or not (cable routing permitted), If they are RCD protected it is thought there is an advantage taking the supply from the lighting circuit.

 

[switch33859]

I thought it was a requirement that fire alarms had their own dedicated circuit not protected by RCD.

"The circuit supplying the fire alarm system should not be protected by an RCD unless this is necessary to comply with the requirements of BS 7671. Where an RCD is necessary for electrical safety, a fault on any other circuit or equipment in the building should not be capable of resulting in isolation of the supply to the fire alarm system."



If it can then can i just have them running off the downstairs RCD.

RCD 1 running --> Cooker, D/s Ring, Kitchen Ring, D/s lights, Fire Alarms
RCD 2 running --> Shower, U/s ring, Garage, U/s lights.

Cheers

 

[londonboy]

not be protected by an RCD unless this is necessary to comply with the requirements of BS 7671.

If the cable is chased into the wall then it needs rcd/rcbo protection.

Personally I think you have two options:
Run radial from cu on surface
Run radial from cu chased into the wall on an rcbo.

Don't just stick it on the same cct as your sockets.

 

[JohnD]

switch33859, we have every sympathy with you, because we know your electrician almost as if he was an old friend. He keeps agreeing to do notifiable work for householders, and asks them to buy the materials and do the design, before going away, so they have to come on here to ask for advice.

I can't think how the poor chap makes a living, because he has been continually out of the country or off sick for the last five years, and can't be contacted by phone.

 

[Pants7478512]

Your options are as Londonboy has suggested.

Are you sure your new consumer unit cannot be configured for some unprotected ways straight off the main switch? This will of course still depend on cable routing.

If you were to go down the RCD route it may be worth using mains radio-interlinked alarms, with one alarm on each lighting circuit, and battery backup.

 

[switch33859]

John D - while i know of many builders/plumbers/sparky's like this - this guy is a dear old friend of mine - an old stick who does a good job because that's all he knows and wants to do.

We did the design late at night at his house 2 days before he was due to leave - my fault for leaving it to late. Just an oversight. But i do understand how you might see my predicament as being created by one of these %^&*'s.

Cheers

 

[switch33859]

This is what i am not sure - at the moment the feeds to both RCDs from the main switch take up quite a lot of space.

Could it be as simple as running additional cables (1 live 1 neutral) from main switch to new RCBO - there is space on the unit - i have a 10 way unit and am only using 8 of the available slots.

What size cable would be required if this is possible.

So Unit would be

Main Switch --> RCD 1
--> RCD 2
--> RCBO

 

[londonboy]

Not allowed.

As I said buy the other board and your electrician will advise further.

 

[Pants7478512]

This will also depend on the type of supply to your property!

If its a TT it will all need RCD protecting anyway.