Can you connect an FCU directly into a ring main?

[Splincher]

Hi,
Can you connect an FCU directly into a ring main? Rather than splitting the ring main and installing a JB I would rather fit the FCU direct.

Cheers

 

[westward10]

You may need to elaborate.

 

[Splincher]

I need to run an extractor fan for the hob in my kitchen, as I live in a bungalow I can easily access the kitchen ring main. So rather than splice the ring main with a junction box I would rather splice it with the actual fused spur unit.

 

[brianmoooore]

Splicing the FCU into the RFC is how it should be done. Using a junction box on anything other than a lighting circuit is a design failure.

 

[littlespark]

Splicing the FCU into the RFC is how it should be done. Using a junction box on anything other than a lighting circuit is a design failure.

Pretty sure a junction box is allowed as a spurring off point on an RFC. Not a design failure if it’s the most suitable way.

 

[brianmoooore]

It's certainly 'allowed', but from the point of view of testing and fault finding, it's better that all joints and connections should be readily accessible
I've reluctantly used junction boxes occasionally when making additions to non lighting circuits, but they should never be used in the initial install.

 

[littlespark]

Whatever’s most suitable for the job.
It sounds like an addition, but if it going beside an existing socket, then spur from the socket, or extend the rfc into the FCU.
Easier to terminate in a one gang box if it’s only one cable in, one cable out.

 

[brianmoooore]

If it is a 2G socket on the RFC, with only two cables present, then I'd spur from that to an adjacent FCU, so that the 1G FCU only has two cables in the more restricted space.

 

[swaRRR]

I get what you mean OP.

Look on Page 505 of the regs book, it shows the two ways of doing FCU's for adding sockets - directly connected and not directly connected to the ring final.

So you can either put the FCU as a point on the ring final or you can come off at some other point into the FCU. It's obviously less cable and fannying about to put it as a point on the ring final.

Interested in others opinions here though since the page i described (505 of the regs book) actually shows an FCU supplying fixed equipment needs to first be spurred off the ring final via a junction box in 2.5mm into the FCU before finally supplying the equipment.

I'm taking it this is just a quirk of the drawing since it should make no difference if you make the FCU part of the ring final and then come off with the supply to the fixed equipment? Adding an extra joint is bad practice surely?

 

[Splincher]

That’s what I thought, but I noticed that the binding screws on a FCU are way smaller than those in a 13 amp socket. After I saw that I thought perhaps running heavy currents through those type of connections was not such a good idea?

 

[nicebutdim]

That’s what I thought, but I noticed that the binding screws on a FCU are way smaller than those in a 13 amp socket. After I saw that I thought perhaps running heavy currents through those type of connections was not such a good idea?

You'll find a great variation in FCUs from one manufacturer to the next, but all should provide ample space for 2x 2,5mm2 conductors in L&N terminals.

 

[Splincher]

Thanks, you’re right. I am using MK but I have now looked at others from Toolstation and Screwfix and they provide room ok but the lockdown screws are half the size of a socket. I would not like to do them up very tight for fear of stripping threads!

 

[nicebutdim]

Thanks, you’re right. I am using MK but I have now looked at others from Toolstation and Screwfix and they provide room ok but the lockdown screws are half the size of a socket. I would not like to do them up very tight for fear of stripping threads!

There should be no issues terminating 2x 2.5mm2 conductors in an MK FCU.