Can I put sockets on a redundant shower radial circuit?

[Dandyman]

Hi,

I would like to put one, maybe two sockets in my loft.

We used to have an electric shower in the bathroom but have since changed to a mixer shower. The cabling is still there, going into the pull-cord switch on the bathroom ceiling; it is on an independent 40 amp radial circuit.

Can I use this circuit for one or two sockets? I understand I may have to swap the breaker for one with fewer amps? The cable used on the circuit is thicker than cable found on sockets, but I assume as long as the wire is too thick and not too thin, this is not a problem?

I wouldn't be doing the work myself, I would get an electrician acquaintance of mine to carry out the work, I would just like to know if my intentions are possible before I call him.

I would be grateful if anybody could advise.

Thanks.

 

[OwainDIYer]

probably yes.

The MCB would usually be taken down to 32A but given the cable is probably larger than that used on a 32A radial the electrician may decide it's not necessary to.

 

[plugwash]

Conventionally the largest breaker used on a socket circuit is 32A, I dunno if there are any regs actually requiring that though.

Also there are physical issues to consider. If the cable is 6mm it should be ok with MK sockets and big backboxes but if it's 10mm you will probablly need to use a junction box to step down to a cable size that will fit the sockets.

 

[sparkwright]

I too would use a 32 amp breaker (or RCBO as the case may be) and would do any additional wiring in 4 mm2 or higher.

Or, if you only happen to have 2.5 mm2 cable, fit a 20 amp.

 

[Dandyman]

Thanks for your replies.

The cable looks to be 10mm.

Having done some research online, a popular option seems to be installing a garage CU in the loft? Is this necessary? Also, am I able to install two sockets or just one?

 

[riveralt]

Thanks for your replies.

The cable looks to be 10mm.

Having done some research online, a popular option seems to be installing a garage CU in the loft? Is this necessary? Also, am I able to install two sockets or just one?

Did the online research not answer that question?

If it wired and fitted correctly you can run as many sockets as you like.

 

[Taylortwocities]

The cable looks to be 10mm.

You'll only be able to get one of those in a socket, and that would be a struggle

Having done some research online, a popular option seems to be installing a garage CU in the loft? Is this necessary? Also, am I able to install two sockets or just one?

That could be done but the CU would not really be readily accessible in the loft. Better to put it in an airing cupboard etc..
The sockets would have to be RCD protected, somewhere.
You could have as many sockets as you like within the rules for ring final or radial circuits.

Remember what a fuse/mcb is for: it is there to protect the cable so the mcb size(s) for the circuits served by the loft CU would have to be appropriate for the cable size that you run the circuit in.

 

[JohnW2]

The cable looks to be 10mm. Having done some research online, a popular option seems to be installing a garage CU in the loft? Is this necessary? Also, am I able to install two sockets or just one?

Assuming that the circuit is already RCD protected, I see no real advantage (and some disadvantages) of using a garage CU - you might as well just use an appropriate junction box to reduce the 10mm² cable (if that's what it is) to a size (2.5mm² or 4mm²) appropriate for wiring the sockets.

You can wire as many sockets, as a 'radial circuit' as you like. However, the MCB you use (hence maximum amount of current to be drawn by all the sockets) is determined by what size cable you use to wire them - 20A if you use 2.5mm² cable or 32A if you use 4mm² cable.

Kind Regards, John

 

[plugwash]

Having done some research online, a popular option seems to be installing a garage CU in the loft? Is this necessary?

It's not strictly nessacery but installing a small CU on the end of the cable can be a good option as CUs are designed to take big cables and it avoids any need to change the breaker in the main CU while also allowing you to use sensible sized cables for the runs to the new sockets.

Also, am I able to install two sockets or just one?

As long as the circuit is properly designed you can install as many sockets as you like.

 

[Dandyman]

Thanks guys.

I think I'd feel better going with the CU option but I'll call my electrician friend tomorrow and see what route he feels is best.

Thanks.

 

[JohnW2]

I think I'd feel better going with the CU option but I'll call my electrician friend tomorrow and see what route he feels is best.

You might find that one of the issue he raises is the 'lack of discrimination' you would probably have between the MCBs in the loft and main CUs - i.e. if there was a fault/overload on the circuit, there would be little telling whether one, the other, or both would trip. I personally don't see that as much of an issue in the situation you're describing, but some people don't like it. I would be interested to hear what your friend advises.

[note: whilst it's true that the garage CU would offer plenty of capacity for the 10mm² cable, the same would be true of appropriate junction boxes]

Kind Regards, John.

 

[Dandyman]

My electrician cannot fit me in for a number of weeks so I'm thinking of doing this myself via the junction box method. I know I'm not an electrician but I'm quite DIY savvy and have wired electrical sockets in the past etc, also, most of the wiring is already there, it's just a case of replacing the circuit breaker to a 20amp and installing the sockets via a junction box.

I know I need a 20amp type B breaker which I have bought. I have opened up the consumer unit (after turning all electric off of course), a question I have regarding this is - the current 40amp breaker that I need to replace just has a brown wire going into it, compared to numerous red and brown wires going into the other breakers - I assume this is because the 40amp breaker is on a radial circuit and the other breakers are on ring circuits? - So is it a case of simply taking the brown cable out of the 40amp breaker and putting it into the new 20amp breaker?

Also, what type of junction box do I need to run the 6mm cable into and the 2.5mm cable out of and to the sockets?

Thanks.

 

[riveralt]

My electrician cannot fit me in for a number of weeks so I'm thinking of doing this myself via the junction box method. I know I'm not an electrician but I'm quite DIY savvy and have wired electrical sockets in the past etc, also, most of the wiring is already there, it's just a case of replacing the circuit breaker to a 20amp and installing the sockets via a junction box.

Not really but what about your testing (Continuity, Insulation resistance, polarity dead/live, PFC, Earth Loop Impedance (external and combined), RCD times etc and certification - required by your Local Authority Building Control? How will integrate your RCD into the circuit?
What is your earthing system? And does it meet the current standards?
Is your main protective bonding in place?

I know I need a 20amp type B breaker which I have bought. I have opened up the consumer unit (after turning all electric off of course), a question I have regarding this is - the current 40amp breaker that I need to replace just has a brown wire going into it, compared to numerous red and brown wires going into the other breakers - I assume this is because the 40amp breaker is on a radial circuit and the other breakers are on ring circuits? - So is it a case of simply taking the brown cable out of the 40amp breaker and putting it into the new 20amp breaker?

No for reasons outlined above.

Also, what type of junction box do I need to run the 6mm cable into and the 2.5mm cable out of and to the sockets?

One that will handle 6mm2 T&E so probably a 60Amp jb.

I really think you should stop now and either wait patiently for your electrician to fit you in or consider hiring someone else - I feel that you have neither the competence nor the equipment to properly and more importantly safely complete this installation.

 

[Dandyman]

Thanks for your response, riveralt.

The circuit is already RCD protected and the house was completely rewired 5 years ago so I would think the earthing system does meet current standards.

The circuit was wired for the shower 5 years ago, professionally, so apart from swapping out the breaker, I assumed adding the sockets would have been similar to adding a spur socket?

 

[riveralt]

Thanks for your response, riveralt.

The circuit is already RCD protected and the house was completely rewired 5 years ago so I would think the earthing system does meet current standards.

You should be able to check that it does meet current standard by examining the first page of the Electrical Installation Certificate, the schedule of Inspections and the schedule of test results, that would have been given to the householder after the rewire.
It should identify what your Earthing system is TT, TNS or TNCS and the sizes of the main earthing cable (16mm2) and the main protective bonding cables (10/16mm2) to your gas and water supplies.

The circuit was wired for the shower 5 years ago, professionally, so apart from swapping out the breaker, I assumed adding the sockets would have been similar to adding a spur socket?

You are changing the circuits characteristics and altering the circuit layout - so it should be tested before it is energised. If you do not have one you can hire testers and obtain certificates from your electrical stores. The work is notifiable to your Local Authority Building Control so you should advise them before you start the work.