Electric towel rail

[bobt]

Hi,
I have an electric towel rail that I'd like to mount in the bathroom. The shower has a pump under the bath that is connected to the CU on its own RCD circuit. At the base of the wall in the room behind the bathroom there is a FSU for the pump. Can I pair up an additional FSU here using the pumps supply to power my 400Watt towel rail? or is it better to create a spur from a socket and use that to connect the FSU to towel rail?

Thanks

 

[Qedelec]

The latter, you can,t have two FCU's off one point

 

[bobt]

Thats what I thought but queried it incase the situation was different for a device running on its own dedicated cable and CU fuse.
We've recently moved and about 18months previous to this the owner had a new central heating system installed by British Gas. Looking and the cabling in the hotwater tank cupboard they've taken a feed from the back of the FSU that supplies the emmersion heater and used that via another FSU to supply the central heating switch gear control box / valves / heating pump etc. This I asume should be on its own circuit.

Thanks

 

[Steve]

FCU! not FSU! i fear an FSU is something totally different.

And as long as the boiler stuff is no more than 3A, you should be ok - most are less than 3A, and your 'mersion should be on a 16A breaker, but it only draws 13A - do the maths yourself

 

[bobt]

But I've just been told by Qedelec that I can't have two FCU's off one point? So why is it 'Ok' to do this for the emersion and boiler but NOT for my shower pump and proposed towel heater?

Thanks

 

[Steve]

the second FCU probably comes from the unfused side of the first one. open up and look.

 

[JohnD]

From your description I gather your shower pump is on a dedicated radial, not a ring.

 

[bobt]

Correct. There is a 2.5mm cable direct from the CU (on its own mcb) to an FCU on the outside of the bathroom wall. Is it 'OK' to take a spur from the unfused side of the FCU to another FCU to power my towel rail?

I probably hadn't made myself clear in my original post as I never intended to run the 2nd FCU from the fused side of the first.

Thanks

 

[bobt]

Sorry for labouring on this question and I really appreciate the comments given so far, but I would like help to understand the reasons why its ok in one situation and not another.

Thanks

 

[JohnD]

A radial circuit is a piece of cable with one appliance on the end, and possibly others along its length like beads on a string. It does not return to the CU like a ring circuit. It can have more than one outlet on it, subject to the capacity of the cable and the fuse or MCB that protects it, but you don't have spurs*, you just put the outlets along its length. This can include one or more FCUs or sockets. However in houses it is unusual to have many sockets on a radial, they're more common for a single load like a cooker, shower or immersion heater.

If your radial just goes to the bathroom I can't see the point in trying to split it into a "Y" shape or have spurs on spurs. just have a look at how it runs and extend it from the end of the circuit.


On a ring circuit you shouldn't put spurs on spurs, because the capacity of the spur is only (about) one 13Amp load. If you put a spur on a spur you can't be sure that there won't be two (or more) 13Amp loads on it.




*There may be some rules for how to put spurs on a radial, but I don't know how.

 

[Qedelec]

Sorry to have confused you Bobt, I read your first post as being a spur off the ring. Not usual to have a dedicated radial for the pump alone.
Make sure it feeds the pump and is not a spur off the ring by carefull testing. Than as already said the loading is ok for a 2.5mm cable and can supply two FCU's. The total fusing of these FCU's must not exceed the rating or protective device for the cable. Don't forget to do a Zs & RCD test on the new provide and complete the certifacation to satisfy LABC

 

[Steve]

A spur on a ring is usually done in 2.5mm² cable - which, at best, can only supply 27A. ring protection is 30 or 32A, so only one double socket or one FCU is permitted - any more has the possibility of overloading it.

However, on a radial run in 2.5mm² - for example, an immersion heater circuit - you can extend the radial, as it were, because the whole lot should be on a 16 or 20A MCB, so the cable is protected - there is no chance of overloading it.

 

[plugwash]

depends on the type of motor. but afaict its not at all unusual for a strugling motor to draw significantly more current than the same motor operating normally.