Spurs


Postby peachy » Mon Jan 25, 2010 6:30 pm

Can you run a spur from a spur? :?
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Postby ericmark » Tue Jan 26, 2010 3:59 pm

If the spur is protected with a FCU then yes.
If direct from 32A ring with no fuse then no.

Look here Google "theiet.org/publishing/wiring-regulations/updates/bs7671-2008-corrigendum-jul08.cfm?type=pdf" to down load correction to regulations at the end is a very handy chart showing exactly what is and what is not allowed.
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Postby peachy » Sat Jan 30, 2010 2:49 pm

Thanks for your reply. Just to clarify and confirm our current situation:we are currently refurbishing bathroom and new shower requires a booster pump to increase the flow and it is situated in the airing cupboard (separate room to bathroom!). We have socket in airing cupboard which is a spur from nearby bedroom. This socket serves TV aerial booster. Anyway, are you confirming that we can run a spur from this socket (itself a spur) as long as it is a fused spur ?(which I understand is an elec requirement of the booster pump). We do have a ciruit breaker on our consumer unit in garage and this is reasonable new (fitted about 7/10 years ago by a professional. If we can do this it would save us a lot of time and trouble!!! Thanks
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Postby ericmark » Sun Jan 31, 2010 10:09 pm

[quote="peachy"]Thanks for your reply. Just to clarify and confirm our current situation:we are currently refurbishing bathroom and new shower requires a booster pump to increase the flow and it is situated in the airing cupboard (separate room to bathroom!). We have socket in airing cupboard which is a spur from nearby bedroom. This socket serves TV aerial booster. Anyway, are you confirming that we can run a spur from this socket (itself a spur) as long as it is a fused spur? (which I understand is an elec requirement of the booster pump).[/quote] The FCU will need to be at origin of first spur not between first spur and second. [quote] We do have a circuit breaker on our consumer unit in garage and this is reasonable new (fitted about 7/10 years ago by a professional. If we can do this it would save us a lot of time and trouble!!! Thanks[/quote]A circuit breaker can be a Switch, Overload, or RCD. It is the latter the RCD that you must now have. A RCD will have a test button and marked 0.03A or 30ma the old 100ma or 0.1A types will not do.
Most likely cure if missing is to fit a RCD FCU at the first socket. Also although your not allowed two single sockets you are allowed a single double socket. Not a clue why but that's the rules.

7/10 years is long time new regulations came in 2001 and 2008 and the latter is quite strict on use of RCD's. I have already given you link. I am sure you will find it easy to understand when down loaded it's very easy to follow.
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Postby peachy » Mon Feb 01, 2010 7:32 pm

thanks for the info, had a look at the iet regs and the diagram showing whats allowed, which was very helpful but still not 100% clear, so just to clarify:
our current spur in the airing cupboard is from the socket in adjoining bedroom, shall we change this spur in the airing cupboard to a fcu and then run a double socket from this and then a further double socket from that!
we do have the 30ma rcd
thanks again!!
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Postby sparx » Thu Feb 04, 2010 10:19 pm

hi, yes thats fine but why not change the existing socket to a double one? it still counts as one point, with aerial booster in one side and shower pump in other. why do you need 2 doubles?
(FYI Putting FCU first then allows an unlimited number of sockets as total load can only be 13A max due to fuse in FCU)
regards Sparx
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Postby peachy » Sat Feb 06, 2010 8:21 pm

Thanks for info, but I've managed to get my wires crossed!!!! On double checking info on booster pump it needs a fused spur. Therefore can I/should I:

* change the spur in the airing cupboard (which has been taken from the socket in bedroom) to an fcu, then run a double socket from this (I need a double) and then can I run a fused switched spur from the double for the pump.?

Thanks again for help
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Postby jimmy_one_ball » Mon Feb 15, 2010 11:14 pm

No mate, the pump is on a plug which is in itself fused so it is protected. You don't need an FCU for a water pump, simply plug it in and off you go. I'd say to check the fuse rating of the plug though, probably a 3A needed. Watts divided by Volts = Amps.
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Postby peachy » Fri Feb 19, 2010 10:06 am

Thanks for all your help, much appreciated.
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Postby oxoid » Tue Feb 23, 2010 12:48 pm

Can someone please explain why it is illegal to run more than one spur from a socket. Surely the combined power used by n sockets,all connected in parrellel, on a spur is no greater than the power consumed by n sockets on a ring or radial circuit. Providing the cabling is of required standard what's the problem?
In fact a radial circuit can be modelled as one socket with n parrellel connections on n spurs.
Or am I being thick. It's a long time since I was edificated in Ohms law
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Postby chris_on_tour2002 » Tue Feb 23, 2010 10:07 pm

oxoid - because all the power being drawn by the spurred sockets could be substantial if all sockets in use at the same time with heavy load appliances. all that power would be passing through the one socket providing the spurs rather than being distributed across the whole ring. this creates a potential fire hazard as temperatures in that circuit could become dangerously high.
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Postby sparx » Wed Feb 24, 2010 7:10 pm

oxoid,

the ring circuit consists of effectively 2 parallel 2.5mm2 cables effectively equaling 5mm2 protected by a 30/32A fuse/mcb.
A spur from the ring being only a single 2.5mm2 conductor needs to be current limited by design, thus it is considered unlikely that a single outlet even if a double socket would have say 2 X 3kW heater on it for example but if a second outlet was connected some distance away this could become the case.
Likewise a radial in 2.5mm2 has to be limited by a 20A device.
Also a radial run in 4mm2 can have only single outlet spurs in 2.5mm2 ,
So in order to protect the spur cables/connections from overload if more than one is required then a fused connection unit must be used at the start of the spur whose 13A fuse will limit the load for all the outlets, just like using a multi outlet extention lead.
Your point about cable being to required standard is the crux of the matter since the design of the standard domestic ring to which we allude states the sizes allowed by the IET.
Anyone who is prepared to design a circuit with all criterior/calcs. to demonstrate safe compliance with the regs can of course do so but this is outside the DIY forums brief I believe,
regards Sparx
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