Circuit Wiring Query 1

[desertfox]

Hi all

I am considering putting a double socket in my garage near to where the distribution board is situated and was considering options of the best way to do this, my first idea was to run a mini ring main with the double socket directly to and from the distribution board, as I have already one spur socket running directly from the board so I can't add anymore spurs.
I know I can extend the ring main and add my sockets as shown in attached diagram B, but I am against this as it means cutting cables and using joint boxes, the neater and cleaner way would be to do my first idea and run a mini ring circuit as in diagram A attached, however I have no spare 30amp fuses, so it would mean connecting two more cables into the existing ring main.
Despite my google searches I can't find a definitive answer as to whether this breaks any regulations or not so I hope someone can help me in here.
I can't see any problem with doing what I prefer, as the fuse is the limiting factor whether I do circuit A or B but I am open to suggestions.
Lastly its probably important to mention I am UK based.

Regards

desertfox

 

[ScottyUK]

Option A is effectively two separate circuits fed from one breaker of fuse. Not pretty. Option B is the correct way to do it. Instead of junction boxes can you either re-cable direct from the other sockets? If you do modify the ring then you really need to check that you can meet the fault clearance times and that the earth loop impedance is sufficiently low.

A "spur socket running directly from the board" sounds suspiciously like a radial circuit and not a spur: different set of rules. A spur is a tap off a ring circuit. Use a 20A fuse and cable direct to the new socket in 2.5mm^2 cable. If the route is short then you will almost certainly not have problems with clearance times or loop impedance. Oh, and it's a new circuit so you'll need to get it checked to Part P of the building regs.

The IEE On-site Guide is a useful reference for domestic and light commercial installations, and is a lot easier to read than the regs themselves.


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If we learn from our mistakes I'm getting a great education!

 

[desertfox]

Hi ScottyUK

Thanks for the input, the sockets are less than 5m from the distribution board and I am only going to plug a freezer into it, the other socket will just be a spare used very infrequently.
I haven't connected to the board yet but I have used 2.5sqmm cable as recommended for sockets and I have looked at the fuse protection chapter in the IEE regulations I found online and I can't see that the fuse won't do its job,
is what I proposed initially outside the regulations only I couldn't see anything that says its prohibited, however I think I'll do method B and ask someone to check the work.

desertfox

 

[ScottyUK]

I can't think of any regs which option A specifcally falls foul of, but it isn't one of the preferred circuit configurations either.

Don't run the radial circuit directly from the 30A ring main fuses - a radial circuit needs a dedicated 20A fuse. If you have access to the 17th Edition there's a helpful diagram in Appendix 15 which shows what is permitted.


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If we learn from our mistakes I'm getting a great education!

 

[desertfox]

Hi Scotty

I've checked that I have a ring main, seperate ones for up and down stairs.
My plan now is just to spur the double socket from the distribution board and that appears to be allowed in the regs.
I suppose doing my option A isn't a good idea because maybe in the future someone else might starts spuring off it and then you have the problem of overloading.

Many years ago I started off as an apprentice electrician but left and went into engineering when they wouldn't send me to college to learn the theory.
Ironically later in life I obtained a HTEC in electrical engineering but I realise that doesn't make me a sparky lol.

Thanks again

desertfox