Add 2nd CU?

dunny · 25 Oct 2021

Hi all,

I am refurbishing my house bit by bit and the next big job is fitting a new kitchen. The whole house needs a rewire and this will be done as I refurbish each area. The house is fairly big so cable runs can be quite long. A couple of years ago I had an electrician install a metal CU and at the moment the only thing this feeds is a compressor in the garage. My intention is to add new circuits to this over time. I could use it now to power up the kitchen but it would be easier (I think) to install a second CU in the boiler cupboard in the kitchen. I could then use 1 CU for one side of the house and 1 CU for the other.

In the kitchen I need 6-8 double sockets (kettle, toaster, microwave, mixer, hoover etc), a separate circuit for the main appliances (fridge, freezer, washing machine, hob), a circuit for the double oven, a circuit for a couple of lights and a circuit to power the boiler controls.

I would like to pull the cables through myself but have some questions please:-

Is my plan to have 5 circuits to the kitchen overkill - is there a better way bearing in mind at the moment it is only the kitchen that will be rewired and it may stay that way for a while. Is a ring mandatory or can I use a radial nowadays?
I assume I would also need to pull a good earth through for coross binding in the kitchen?
Can I add a second CU to power this side of the house and if so what cabling would I need to pull through to wire it up? Does the cable come from the first CU or through a separate isolator like my existing one does?
When it comes to wiring up the lights can you still wire these at a JB or do I now need to pull down two cables per light switch?
Is there an issue with having 2 CU's both which have an RCD circuit on them?
Is there anything I am missing?

I have no problem paying the electrician to wire everything up and test at the end but since I am lifting floors for plumbing I would like to get the cables in ready myself if possible.

I have uploaded a couple of pictures of the CU I had fitted a couple of years ago if that will help. The mess above it will all be decommissioned over time.

Thanks

Dave

Harry Bloomfield · 25 Oct 2021

dunny said:
Is my plan to have 5 circuits to the kitchen overkill - is there a better way bearing in mind at the moment it is only the kitchen that will be rewired and it may stay that way for a while. Is a ring mandatory or can I use a radial nowadays?

No, five is reasonable - but I would suggest separating the fridges and freezers to have their own circuit, with nothing else on it. That avoids that circuit tripping if there should be a fault on another item and losing the contents of your freezer.

Avoid JB's - either two/three cables at the ceiling, or the more modern method at the switch - for things which need a neutral at the switch.

dunny · 25 Oct 2021

Harry Bloomfield said:
Avoid JB's - either two/three cables at the ceiling, or the more modern method at the switch - for things which need a neutral at the switch.

Is the modern method now a supply coming into switch from previous light rose, cable up to new light rose, neutrals joined at the switch, and live split at the switch?? So in terms of cables I would have an incoming supply at the rose, a supply down to the switch position, a cable back to the rose and a cable to the next light from the rose? So 4 cables at each rose and 2 at each switch up to the last rose which would have just 3 cables? Or is it all done at the switch so supply cable down to first switch, neutrals joined, cable back to light and third from the switch position to the next switch?

I assume the latter?

EFLImpudence · 25 Oct 2021

dunny said:
Is a ring mandatory or can I use a radial nowadays?

Rings are not mandatory.
Up to you. It depends on the location; no point having a ring with both legs in the same place.

I assume I would also need to pull a good earth through for cross binding in the kitchen?

No such thing as cross-bonding.
Bonding is not required in a kitchen - unless a metal supply pipe emerges from the floor in that kitchen.

Can I add a second CU to power this side of the house and if so what cabling would I need to pull through to wire it up? Does the cable come from the first CU or through a separate isolator like my existing one does?

You can have a second CU if you want.
The cable must be large enough for the demand - if you conceal the cable in such a way that it must be RCD protected, you will have to use a cable (e.g. Armoured) which does not need RCD protection.

When it comes to wiring up the lights can you still wire these at a JB or do I now need to pull down two cables per light switch?

There is no prescribed method.

Is there an issue with having 2 CU's both which have an RCD circuit on them?

No. Not sure what you mean as virtually all circuits require RCD cover nowadays.

Is there anything I am missing?

Probably.

I have no problem paying the electrician to wire everything up and test at the end but since I am lifting floors for plumbing I would like to get the cables in ready myself if possible.

It doesn't work like that.
You must employ a registered electrician before you start so that he knows what has been done.[/quote]

EFLImpudence · 25 Oct 2021

Is there an issue with having 2 CU's both which have an RCD circuit on them?

Ah, I think you mean what I mentioned above.

You do not want the kitchen CU supplied from an RCD protected way in the existing CU.

dunny · 25 Oct 2021

Thanks for the reply.

JohnW2 · 25 Oct 2021

Harry Bloomfield said:
.... but I would suggest separating the fridges and freezers to have their own circuit, with nothing else on it. That avoids that circuit tripping if there should be a fault on another item and losing the contents of your freezer.

As we've been recently discussing, I personally would advise against (literally) "... with nothing else on it". I would personally favour the fridge/freezer circuit also supply something (maybe something like under-cupboard lighting) who failure would be likely to be noticed fairly quickly - since, otherwise, the fridge/freezer circuit might remain 'dead' (due to operation of a protective device) for quite a long time before anyone noticed.

Kind Regards, John

dunny · 25 Oct 2021

EFLImpudence said:
No such thing as cross-bonding.
Bonding is not required in a kitchen - unless a metal supply pipe emerges from the floor in that kitchen.

The main incoming water supply is lead which then goes to copper so I assumed it would need earth bonding. I was therefore planning to pull an earth through all the way to this incoming pipe.

winston1 · 25 Oct 2021

The boiler controls don't need their own circuit. They can be powered from a ring via a FCU.
Installing a CU is notifiable work.

dunny · 25 Oct 2021

Thanks

JohnW2 · 25 Oct 2021

winston1 said:
Installing a CU is notifiable work.

It should be, but 'the law' only says that replacing a CU is notifiable.

However, installing 'new circuits' is notifiable - so, whilst if the rules/law were taken literally, installing a new (additional) CU, per se, would not be notifiable, installing any circuits from it would be.

I don't think that the rules are intended to make sense!

EFLImpudence · 25 Oct 2021

dunny said:
The main incoming water supply is lead which then goes to copper so I assumed it would need earth bonding. I was therefore planning to pull an earth through all the way to this incoming pipe.

Sorry, I was assuming the 'new' kitchen was in a 'new' place.

Is the pipe not already Bonded?

If not, then yes you will need a 10mm² cable.
However, if the new supply cable has a 10mm² (or larger) CPC (earth wire) then you can use that.

You really must get a registered electrician to supervise all this so that he is satisfied to sign the paperwork.

Harry Bloomfield · 25 Oct 2021

JohnW2 said:
As we've been recently discussing, I personally would advise against (literally) "... with nothing else on it". I would personally favour the fridge/freezer circuit also supply something (maybe something like under-cupboard lighting) who failure would be likely to be noticed fairly quickly - since, otherwise, the fridge/freezer circuit might remain 'dead' (due to operation of a protective device) for quite a long time before anyone noticed.

Or even better, a power failed alarm.

dunny · 25 Oct 2021

EFLImpudence said:
Sorry, I was assuming the 'new' kitchen was in a 'new' place.

Is the pipe not already Bonded?

If not, then yes you will need a 10mm² cable.
However, if the new supply cable has a 10mm² (or larger) CPC (earth wire) then you can use that.

You really must get a registered electrician to supervise all this so that he is satisfied to sign the paperwork.

No, the pipe is not bonded unfortunately. Earths anywhere in this house seem very hit and miss!! I have begun to realise that I would be best getting a plan from a spark. Its just that I want to get the cabling in asap as I am on a bit of a deadline and its proven difficult to actually get a spark out in the past!! I knew I needed one for the power up of course as I want it to be right!!

Thanks

JohnW2 · 25 Oct 2021

Harry Bloomfield said:
Or even better, a power failed alarm.

Sure - that was also part of our other discussion.

However, as I said, in the case of freezers even a power failure alarm is not good enough (i.e. satisfactory) for me! As I said, had I been reliant on power failure alarms, I could well have lost two or three freezers full of food over the past 2-3 decades, since the failures were of the the freezers themselves, with power still present - hence I have (battery powered) over-temp alarms on all my freezers.

Since it's the temp that matters, regardless of whether or not there is power, why not have an alarm which senses that? Let's face it, if the freezer is in a garage or outhouse etc., the problem could be due to someone having left the door/lid open

Kind Regards, John

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