Reusing a circuit

[ADringer]

Hi All,

I was planning on installing some underfloor heating running a fused spur off an existing socket. Yesterday I got round to actually looking at the socket I was going to spur from and realised it's already a spur.

I did have an electric shower on it's own circuit which has now been removed. I was thinking possibly using this to create a circuit specifically for underfloor heating as I might get some more at a later point (recently bought the house and am doing it up).

Some questions:

1. Some heating will be downstairs, some will be upstairs. Is this against regulations for a circuit to be over two floors?

2. I believe using an existing circuit does not fall under Part P. What if I needed to change the existing cable coming out of the CU?

3. Generally, what is the best way forward?

Thanks

Alex

 

[PrenticeBoyofDerry]

1. Some heating will be downstairs, some will be upstairs. Is this against regulations for a circuit to be over two floors?

No, but do read the manufactures instruction regarding the system you install, ideally local isolation for each zone would be advised

2. I believe using an existing circuit does not fall under Part P. What if I needed to change the existing cable coming out of the CU?

Part P is a building regulation and all domestic electrical installations fall under that regulation. The use of an existing circuit would not be considered notifiable, providing this was not to be used within the zones of a bathroom.

3. Generally, what is the best way forward?

Employ an electrician that can give you informed advice and prove that any existing circuits are suitable and safe for continued use/re-use.

 

[plugwash]

1. Some heating will be downstairs, some will be upstairs. Is this against regulations for a circuit to be over two floors?

No

2. I believe using an existing circuit does not fall under Part P. What if I needed to change the existing cable coming out of the CU?

All electrical work falls under part P, I suspect what you really meant to ask is whether it was notifable.

Installing a new circuit is notifiable. Afaict where "modifying an existing circuit" ends and "installing a new circuit" begins is not formally defined.

Work is also be notifiable if it's within a certain distance of a bath or shower or if it is in a room containing a swimming pool or sauna heater.

 

[ADringer]

I'm now thinking I will create a spur using a junction box on the existing circuit and just connect up my fused spur to this. This will save me from having to touch the consumer unit.

Any possible issues with doing this?

Thanks

 

[Iggifer]

nope so long as the junction box is accessible, or if not, a maintenance free one is used.

I would stick with leaving it accessible though, saves a lot of hassle in the future

 

[riveralt]

I'm now thinking I will create a spur using a junction box on the existing circuit and just connect up my fused spur to this. This will save me from having to touch the consumer unit.

Any possible issues with doing this?

Thanks

You have to follow the manufacturers instructions - while some do allow FCU's to be used they require an electrician to make an assessment of the likely load on the circuit.
They also require the circuit to be covered by an RCD and that the total circuit covered by the RCD is limited to a max of 4.8kw (around 20Amps in old money)
In all the recent installations where I have fitted electric under floor heating I have installed a new RCBO 16Amp circuit for each floor.

 

[ADringer]

Right - had another idea!

From what I've read on this site I think I can quite easily reuse the shower circuit:

1. Change the MCB from 40A to 32A as it's 6mm cable (The other socket circuits are 32A but I did read that it should be 16A/20A?)

2. Add a junction box on the 6mm and run a 2.5mm cable to the underfloor heating. As per manufacturers guidelines, this will be via a FCU

This can be done within the floorboards (I'll be using a maintenance free junction box) which I'm happy with as I won't have to chase cables.

I've never had to get a MCB changed, can a DIYer change it quite easily?

Thanks

 

[riveralt]

Right - had another idea!

From what I've read on this site I think I can quite easily reuse the shower circuit:

1. Change the MCB from 40A to 32A as it's 6mm cable (The other socket circuits are 32A but I did read that it should be 16A/20A?)

Change it to a 16/20A - as per manufacturers instructions. The MCB is there to protect the cable.

2. Add a junction box on the 6mm and run a 2.5mm cable to the underfloor heating. As per manufacturers guidelines, this will be via a FCU

Provided the load doesn't exceed 13A.

This can be done within the floorboards (I'll be using a maintenance free junction box) which I'm happy with as I won't have to chase cables.

Personally I site a sunken junction box next to the FCU and put a blanking plate on it for easy access.
Something like: http://www.tlc-direct.co.uk/Products/AP636.html

I've never had to get a MCB changed, can a DIYer change it quite easily?

Yes provided you can get the correct MCB and that you realise that even when you turn the Consumer Units main switch off - there are still live cables inside.
You will also need the appropriate tester that can measure continuity and more importantly insulation resistance - these figures are required by the manufacturer for their guarantee.
Finally none of this will safely happen unless the circuit is protected by an RCD. If the circuit is not protected by an RCD then you other option is to replace the MCB with an RCBO - provided your CU will accept this - though this may mean a change in the buz bar configuration.

 

[JohnW2]

1. Change the MCB from 40A to 32A as it's 6mm cable (The other socket circuits are 32A but I did read that it should be 16A/20A?)

Change it to a 16/20A - as per manufacturers instructions. The MCB is there to protect the cable.

I agree that one should comply with the manufacturer's instructions, but could you perhaps help me understand what you intended to convey by adding that second sentence? If one were working on the basis that "The MCB is there to protect the cable" (rather than on the basis of the MIs), one obviously would not need to go down to a 16/20A cable to protect 6mm² cable.

Kind Regards, John

 

[EFLImpudence]

Right - had another idea!

Not the way to proceed.

From what I've read on this site I think I can quite easily reuse the shower circuit:

Yes. It is a cable.

1. Change the MCB from 40A to 32A as it's 6mm cable

That makes no sense.

(The other socket circuits are 32A

This was not a socket circuit.

but I did read that it should be 16A/20A?)

Where? Why would the manufacturer require 16A or 20A?
Either it is a fusing maximum stipulation in which case the lower is not necessary or
it is a supply minimum stipulation in which case the higher is not necessary.

2. Add a junction box on the 6mm and run a 2.5mm cable to the underfloor heating. As per manufacturers guidelines, this will be via a FCU

If you use an FCU (13A) then 1.5mm² would be adequate but then the above (16/20) does not apply.

This can be done within the floorboards (I'll be using a maintenance free junction box) which I'm happy with as I won't have to chase cables.

Ok.

I've never had to get a MCB changed, can a DIYer change it quite easily?

As above regards testing so No.