You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
I know there are a few very knowledgable sparkies in here so a query if I may...
We've an old garage / barn with it's own fuse board / RCD. There is a ring main for downstairs sockets on one fuse and I'd like to add a new double socket or two above my workbench.
However, on the same fuse and wired straight from the board is a single cable feeding a double socket upstairs. So the fuse is feeding both a ring main and a single spur. The spur is very close to where I want my new sockets so the question is a) can I add any more sockets to the spur or b) can I convert the spur into a second ring main so there are 2 ring mains running off one fuse?
I would convert the spur into a ring. I am a diyer not a trained sparky and I doubt it would meet regs
You can do either.
Fit an extended radial or change it to a ring main.
A spur comes off another socket. But if it has its own breaker it’s a radial circuit.
So disconnect it from that breaker and fit it to its own circuit.
The radial should be protected with a 16 amp breaker and expected load should not exceed this.
Changing to a ring in a barn should be easy enough as everything is surface mounted (I assume)
Personally I would make it one ring circuit. Run a cable from the upstairs spur to your new sockets then run a cable from your new socket to the last socket in your downstairs ring to make one big ring. Disconnect the ring feed from that downstairs socket so you only have 2 cables connected.
Alternatively if you have a spare way on your board create a separate ring for upstairs.
Just noticed you used the word fuses. If the board has rewirable fuses I would replace it with a modern consumer unit with some spare ways on it and create two ring circuits. Fuses aren’t great much better with circuit breakers.
The radial should be protected with a 16 amp breaker and expected load should not exceed this.
Assuming it's using 2.5mm twin and earth. You could use a thicker guage cable and run a higher current.
I’d never run more than 2.5 to a domestic socket.
4mm radials rather than 2.5mm ring are pretty normal these days
I'd be concerned with the current set up. What rating is the fuse? The single spur should be on a 16a and the ring on 30a so it is either too big for one or too small for the other.
Extending the ring and incorporating the existing spur and new sockets is probably the simplest solution to get something decent.
Other solutions will depend on fuse and cable sizes but I wouldn't just spur more sockets off the existing spur
DIYer, not a sparky.
It really depends on the load you're putting on the spur/2 extra sockets. If you're welding or similar then I'd turn it into a separate ring or extend the existing ring to incorporate it. If it's for a radio/speaker I would just extend the spur.
We have a spur off a socket in the ring but it's only used for charging phones and laptops.
In theory I guess two parallel rings should be ok but I expect it's not to regs. .
As others have said if you want two rings then I'd be swapping out the consumer unit for something more modern with more capacity.
Although to my mind, as your consumer unit in the garage/barn is just coming off one fuse/breaker from the main consumer unit that's that's the weakest link in the chain. It doesn't really care if downstream is a ring or a bunch of spurs....
As I say I'm not a sparky so take that with a large pinch of salt.
To answer some questions:
Modern consumer unit
16A at present (so yes, too small for ring)
No welding just general power tools but may run a small hoist in the garage and that will pull a bit of power.
Sounds like converting to single ring on 30A is the best way forward for what I need (as it is all surface mounted across joists etc so very easy access).
Thanks folks - very helpful.
DIYer, not a sparky.
It really depends on the load you’re putting on the spur/2 extra sockets. If you’re welding or similar then I’d turn it into a separate ring or extend the existing ring to incorporate it. If it’s for a radio/speaker I would just extend the spur.
Also diy here not spark, but also an electronic engineer so understand the principles.
You must not spur off a spur from a ring.
The purpose of the fuse/circuit breaker/mcb is to protect the cable from overloading. A ring circuit is typically protected by a 32A mcb. One 2.5mm2 t+e cannot safely take 32A (without potentially overheating and starting a fire… in a barn), but the load is shared across two cables in a ring so this is ok. A single spur can be taken off a ring, because it’s not possible to load it by more than 2X13=26A on a double socket. If you daisy chain another spur then it possible to plug in enough appliances to overload the 2.5 t+e and cause catastrophic failure.
Thanks for the info goldfish24 👍
Scrap all that! More investigation reveals we’ve got a radial plus a radial with 2 spurs. All run off 16A.
Best thing looks like convert it all to a single ring.
You’re welcome Jeffl.
OP. Aha! So it’s a 16A radial.
Well, the good news is, a radial with a 16A mcb is a pretty safe circuit to go adding sockets to, when using ordinary 2.5mm t+e. And you’re allowed to do it without any building regs signoff (unless it’s in a special location). It’s hard to connect things in such a manner that the cable can ever be overloaded, because it’s protected by a 16A limit well within the operating window of the 2.5mm2 t+e.
So, as long as you’re not operating more than 16A just add your sockets off the one upstairs and job jobbed. Check your work with a cheap socket tester.
If you want more than 16A, then you could take the option you’ve proposed here and convert to a ring. I’d advise against this. Several reasons - it’s notifiable work under building regs. That means it needs doing properly and testing with special equipment. The only practical way to do that is to employ an electrician. Second reason, it’s genuinely quite possible for an amateur to make a non-obvious mistake that can leave a ring circuit in a dangerous state and a potential fire hazard.
Safer bet would be to add a separate 16A mcb for a second radial. (Also notifiable if you’re sticking to the rules)
Safest bet employ an electrician.
I mentioned I’m an electronic engineer, but not what I design - fire detectors. I know that the leading cause of fatality from fire is electrical faults. I employ an electrician to do my electrics at home, despite having a doctorate in electronics.
@goldfish24 - sounds simpler than I thought.
OK to add 4 sockets off the single radial arm (i.e. 2x 2 gang)? Not because I'll be running lots of stuff at the same time, just for convenience above the workbench.
@goldfish24 thanks, useful info for me too, as I'm about to add some sockets to my garage. I currently have a radial circuit on a 16A breaker. Obviously you can only ever pull 16A through that before the breaker trips, so its pretty safe, as you say, but is there any limit in the regs to how many sockets you can add to the radial? I was planning to add quite a few, for the same reason as the OP - rarely use much power at any one time, but handy to have plenty of sockets to leave stuff plugged into rather than switching them over all the time.
Good to know it's not notifiable either. Still apply if one of the sockets is outside? I was going to get the spark to sign them off when he does the kitchen soon. Alternatively, I could get him to change it to a ring. Also want to get him to put a non-latching RCD in.
Just to repeat, I am not an electrician, my knowledge of wiring regs is part DIY, partly because my profession overlaps. I’d be very happy and not entirely surprised to be corrected if a real spark turns up at some point.
I know that wiring regs allows you unlimited sockets on a radial. Just googled it to double check. Fill yer boots. Yes it’s handy to have sockets where you need them, and 16A is often plenty unless you have big workshop equipment.
I understand that you can add sockets to an existing circuit without notification. This includes adding a spur to a ring(a spur must not be more than 1 double socket as above) or extending a radial.
The above no longer applies in certain areas - outside, kitchens, bathrooms. Anywhere wet. And outside includes outbuildings. They become notifiable. I don’t know if a barn counts as an outbuilding. It all goes a bit grey to me.
You explicitly cannot add a new circuit. That would cover replacing a radial with a ring. Basically anything that involves going into the consumer unit (aka fuse board) and changing things.
The rules can be downloaded here: https://www.gov.uk/government/publications/electrical-safety-approved-document-p
Electricians seem expensive, but they’ve trained in all this stuff. The good ones have remembered it.
If fitting sockets yourself, It is sensible to use an inexpensive socket tester to prove that you have wired polarity correctly and have a good earth.
The above no longer applies in certain areas – outside. And outside includes outbuildings. They become notifiable. I don’t know if a barn counts as an outbuilding. It all goes a bit grey to me.
Depends where you are but in England installing sockets outside is not notifiable now. Pretty much the only notifiable location is in the bathroom (and swimming pools and spas)
Thanks again and socket tester ordered!
@goldfish24 cheers, good of you to answer since I could probably have googled myself if I was less lazy. Agree about electricians. I'm loathe to pay people to do things I could do myself, but I'll certainly get it checked when I'm done, even if it's non-notifiable. FWIW, I have a doctorate electr(ical) engineering too, but I know plenty who also do who I wouldn't let anywhere near a socket with a screwdriver in their hand!
Depends where you are but in England installing sockets outside is not notifiable now.
Aha cheers Nickjb.