Is it permissable to have more than one spur coming off a ring at a single point? I want to spur off to a boiler and a double socket, and it would be much more convenient to use a single junction box.
- posted
15 years ago
Spurs from a ring
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- posted
15 years ago
If you take a spur to a FCU first, you can then have several sockets from that single spur. If you don't add an FCU, you can only have 1 socket from that spur.
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- posted
15 years ago
Yes, that's permitted, subject to consideration of the likely loading in relation to the as-installed rating of each leg of the ring circuit cable. In this case the loading of the boiler spur is likely to be quite light so the situation isn't very different from an ordinary double-socket spur.
Check the terminal capacity of your junction box though.
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- posted
15 years ago
Permissible, yup; can be tricky to get all the wires in though depending on the brand of socket etc.
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- posted
15 years ago
Doesnt it depend on the power of the boiler, How many watts is it? How thick are the wires on the ring, how many sockets on it, what size fuse does it come from?
Dont boilers usually have their own fat radial circuit?
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- posted
15 years ago
It's a gas boiler. The electricity supply is for the pump (a few ? tens? of watts) and the control circuitry (maybe one watt).
Normal T+E. Appropriate fuse.
You are thinking of immersion heaters I suspect.
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- posted
15 years ago
I had thought of that (I've played this sort of game in the past). That's why the spurs were going to come off a junction box :-)
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- posted
15 years ago
If we are talking a gas/oil boiler then not really - they are only going to be a few hundred watts at most.
That plays out in a number of ways...
The physical connection issue - which is more a case of selecting the right type or brand of accessory to make getting 4 sets of wires into the terminals easier.
The wires on the ring itself will usually be 2.5mm^2 T&E, however you may encounter some 4mm^2 if there was a particular reason for de-rating the cable.
The other issue is with older cables using 1mm^2 earth wires rather than the moderm 1.5mm^2 type. Here you need to take care with spurs if you have rewireable fuses since the single run of cable on the spur is not adequately fault protected by the fuse.
An unfused spur may only have one socket (double or single). However the quwstion here was about two separate spurs - but taken from the same point on the ring. In this case its not an issue sine one of the spurs is such a low demand. However in a more general sense one needs to look carefully if placing two general spurs in this way that you a are not in danger of overloading a single leg of the ring with a high point load too near to one end or the other.
The largest fuse that would normally protect a ring circuit is 30/32A. With modern 2.5mm^2 T&E that provides adequate fault (i.e. short circuit) protection for the spur's cable. The fusing in the plugs / FCU will provide the overcurrent protection for the spur cable.
Own radial, often yes; fat (as in high current) not typically (unless you were talking about an immersion heater circuit - but even those are often on 15A or thereabouts - less than the design load of a double socket).
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- posted
15 years ago
g: >> Dont boilers usually have their own fat radial circuit?
JR: > Own radial, often yes; fat (as in high current) not typically (unless
Oh yes, sorry, I forgot about gas, we don't get it here, I'd assumed the OP was heating lots of water with electricity as I hope to do (after I've got the cold water system mended and improved) [g]