Supplying two loads (FCUs) from a spur

[LiamPope]

Hi,

Just want to check I have this straight.

Helping a friend install a shower pump in the airing cupboard. Only practical supply option is a spur from a ring which currently terminates with an FCU with a 3 or 5A fuse (I assume, for now, as I couldn't pull it due to it's silly location!) supplying a central heating controller and peripherals.

Am I right thinking I cant simply feed another 3A FCU from the supply side of this existing FCU for the shower pump, as I'll have a spur from a spur situation, but I could add two additional FCUs: A 13A FCU which I'll put the existing spur cable into (removing it from the existing FCU) which will form a 13A fused spur from the ring, and another 3A FCU. I'll then supply the 3A FCU for the shower pump and the existing central heating FCU from the load side of the 'master' 13A FCU.

Sound about right? Seems silly to have to add two additional FCUs for one new load, but I guess I do...

Cheers,

Liam

 

[Spark123]

You are correct in that you should not have a spur from a spur, what you suggest to get around this by adding a 13A FCU to protect the spur is fine.

 

[LiamPope]

Cheers.

 

[OwainDIYer]

Your suggestion of a 13A to two 3A FCUs is fully compliant

However in this case (inside an airing cupboard) with both FCUs being close together, unlikely to be used for any other purpose, and the nature of the loads being unlikely to increase, two adjacent 3A FCUs appropriately labelled would not IMO be unsafe. It would not however be compliant under the 'standard circuit'.

The main risk would be someone using the FCU to supply an immersion heater if the immersion heater circuit failed. Hence the appropriate labelling.

 

[ajrobb]

Would another alternative be to replace the existing FCU with a double gang socket? (This would require that the spur was run in 2.5 sqmm cable.)

 

[ban-all-sheds]

two adjacent 3A FCUs appropriately labelled would not IMO be unsafe.

But you'd have created a situation which could easily be made unsafe.

It would not however be compliant under the 'standard circuit'.

Nor would it be compliant with the Wiring Regulations.

 

[LiamPope]

Cheers for the suggestions. I think I'll go by the book to play safe.

Hard to see what would be wrong in principle with, say, a twin backbox with the two FCUs for CH and shower pump, though. Even if somebody later changed the fuses for 13A and used them to supply bigger loads, it's no different in principle to providing a double socket on the spur which could also be used to supply two 13A loads, but would comply with regs. Oh well - regs are regs

 

[ban-all-sheds]

Even if somebody later changed the fuses for 13A and used them to supply bigger loads, it's no different in principle to providing a double socket on the spur which could also be used to supply two 13A loads.

Except that a double socket may not be used to supply 2 x 13A loads....

 

[LiamPope]

Even if somebody later changed the fuses for 13A and used them to supply bigger loads, it's no different in principle to providing a double socket on the spur which could also be used to supply two 13A loads.

Except that a double socket may not be used to supply 2 x 13A loads....

I know that, but I dare say many people don't, and so the situation could well arise in practice, probably much more easily than somebody replacing 3/5A fuses in two FCUs with 13A fuses and connecting ~13A loads. Yet only the latter situation is prevented by a fully compliant installation.