Can I spur a spur from a spur?

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oldbutnotdead

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Catchy title and it isn't as shoddy as it sounds- should read 'Can I spur an FCU from an FCU' but it wasn't nearly as catchy

BCO has thrown me a wee curveball- he's just told me I need an extract fan in the utility room as part of other works (because the window was changed 2 years ago- why did I ever take this project on? I must be mad).

Anyway, there is a convenient power supply (ring final) in a double single backbox- 1 x 13A 1g socket and next to it a DP FCU for an outside socket. The DP FCU at the moment is spurred (2.5mm singles) from the 13A socket. Can I spur from that DP FCU to another DP FCU (Plan A to run this poxy 30 litre/second nuisance that'll never get switched on) or do I need to incorporate the first FCU into the ring (Plan B) before I can spur from it? Or is it even better practice to continue the ring through the 2nd FCU (Plan C) Pic attached- ish
spur spur spur.jpg

Ta for assistance- I've had a quick flick through the onsite guide but it wasn't that helpful. Downside for Plan C is pulling out a lump of Celotex which is rather tightly fitted between studs- very likely I'll have to wreck it to extract it.
 
Plan A you cannot do. It is a spur from a spur.

There are two options.

Plan B (as you describe) incorporate the FCU for the outside socket into the ring. Then you can spur the new FCU off that.
Plan C connect the new FCU to the LOAD side of the existing FCU. (all your other plans talk about spurs etc on the FEED side of the FCUs….)
 
Realistically, if you are already limiting the possible current on the outside socket (double?) by way of the 13A fuse in the FCU, adding the tiny load of an extractor fan is extremely unlikely to be risking overloading the spur cable, assuming it's 2.5 sq. mm, unless it's had to be derated by a huge amount.

And aren't the spur regulations from former editions of BS7671 now replaced by mere guidelines and recommendations anyway, so it would still be compliant if that was an issue?
 
Cheers all- yes has a feeling that Plan A wasn't a goer, Plan B is easy enough to implement so think that's the way forward.

TaylorTwoCities- yes I thought about that one but want to avoid having to have the outside power on for the extract to work (even though it is never going to get used :) )

deadshort- also considered that one but I don't want the thing running every time I turn the light on (it is total overkill, the major source of vapour in the room is a tumble dryer which has its own vent to outside). One thing BCO was specific about (and to be fair the ADs require it as well)- they're not bothered about overrun on light or humidistat but it must have a manual on/off control. Cheap fans I've looked at don't have a manual override....

PBC_1966- yeah, think you're right but I'll go for the 'definitely acceptable easy to understand' approach of Plan B. Outside socket is a single, it's there for badness (no specific requirement but always handy to be able to plug something in without having to leave door/window open)

winston1- wasn't sure about the legitimacy of that trick and ramming 4 x 2.5s into the back of the socket is going to be zero fun, think I'll go Plan B (or maybe Plan C if the insulation board will ease out sort of nice like :) )

Ta all
 
PBC_1966 said:
Realistically, if you are already limiting the possible current on the outside socket (double?) by way of the 13A fuse in the FCU, adding the tiny load of an extractor fan is extremely unlikely to be risking overloading the spur cable, assuming it's 2.5 sq. mm, unless it's had to be derated by a huge amount.
Click to expand...
I have to sympathise with that view. To consider doing things which might compromise safety (like trying to cram 4 conductors into the terminals of a socket) simply so that one could say that one had complied strictly with regulations would seem to be rather flying in the face of the spirit and purpose of those regulations.

Kind Regards, John
 
deadshort said:
Plan C wire it to the lighting circuit.

Regards,

DS
Click to expand...
He has already said there is a window and it would seem it does not open which is why he needs the fan. So the fan MUST be able to run without the lights being on. It was seem silly to run from the lights in that case, as it still needs some method of turning it on. There is nothing wrong in feeding one fuse connection unit from another, this is a standard method with shed wiring. 13A feeds shed and a 5A switched FCU is used for lights.

With a fan even a 1A fuse will not protect the fan but it will ensure any fault will not cause the 13A fuse to rupture and allow the fan to be isolated.

I was surprised when I read the regulations there is nothing to say you can't use a simple on/off switch with the fan. You can simply tell people to return to room 15 minutes latter and turn off the fan. However if it is automated then a timer is required to ensure it runs on. The simple pneumatic timer to me is ample. As said no one will ever push it anyway.

The problem is with open flue fires, it is unclear as to where in the house that fire can be to affect if a simple extractor can be used? It depends on the house and how many and where the air bricks are to allow air to enter the house. Only safe way is a heat recovery unit.
 
There's a window and it opens but that makes no odds- because I replaced the original window (quite a nice wood-framed one, trying to remember where I've put it now cos it wasn't in bad nick and came out in one piece) with a new DG window and door I've made a 'material change' which means I have to comply with current 'new' requirements rather than make ventilation no worse than it was before.

And I had to read the regs quite carefully and found to my surprise that the only requirement was a manual override- all the rest (timer, humidity etc) were 'could' and 'should'. And then confirmed this with BCO- 'you can have whatever automatic control you like or none at all, all we require is accessible manual on/off''
 
ericmark said:
I was surprised when I read the regulations there is nothing to say you can't use a simple on/off switch with the fan.
Click to expand...
I suppose that's not materially different from the fact that the regs can't realistically expect to 'insist' that an 'openable window', if present, is ever opened!

Kind Regards, John
 
ericmark said:
deadshort said:
Plan C wire it to the lighting circuit.

Regards,

DS
Click to expand...
He has already said there is a window and it would seem it does not open which is why he needs the fan. So the fan MUST be able to run without the lights being on. It was seem silly to run from the lights in that case, as it still needs some method of turning it on. There is nothing wrong in feeding one fuse connection unit from another, this is a standard method with shed wiring. 13A feeds shed and a 5A switched FCU is used for lights.

Did i say from the SL ?

DS
Click to expand...
 
oldbutnotdead said:
And I had to read the regs quite carefully and found to my surprise that the only requirement was a manual override- all the rest (timer, humidity etc) were 'could' and 'should'.'
Click to expand...
All of the "could" suggestions about timers, possibly linking to a light and so on are just guidelines in the Approved Document, not regulations anyway.

The actual regulation requires only that adequate means of ventilation be provided. If any building inspector wanted to try and argue that providing a suitably sized fan which is just switched on manually when required doesn't satisfy that regulation, I'd be demanding that he show me exactly where any regulation says so.
 
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