FCUs

Ash · Nov 2, 2010

So this is bugging me beyond belief now.

In college we were taught to wire the ring then bring the FCU off separately to feed a spur.

I'm in work now being trained and atm we do kitchens. All the FCUs feeding the spurs to the fixed appliances are connected to the ring directly, and in an instance where I cut a wire too short, I suggested connecting it non-directly to which I was told this doesn't work.

It threw me, because I've done my own stuff where I used the method I was taught and it all worked fine.

I've been reading guides, the regulations and all sorts trying to find out if his method is what I'm meant to be doing, but nothing is clear enough.

From my thoughts, the FCU is literally just a fuse, so why does it need to be connected to the ring. Essentially if you put and unfused spur off a socket outlet, then put the FCU between it all you are doing is putting a fuse between it. So why does the fuse need to be connected to the ring?

This brings me to another question, can you have multiple FCUs coming from one socket outlet on the ring as long as they are all connected parallel like a radial circuit. The regs says you can have unlimited unfused spurs, so putting multiple fuses before all the spurs, is that allowed?

I didn't really want to argue this with the electrician training me, because I don't think that would bode well in the long run.

Apache · Nov 2, 2010

Is a proper spark formulating you an answer?

You can put a FCU in the ring - basically all you are doing is cutting the wire and re-joining the terminals in the FCU, giving it it's supply. Or you could spur to the FCU - either just as acceptable and I assume most would do what is most convenient (ie a bit of both). If you put the FCU in the ring you have 2 wires per terminal, take it at a socket you have 3. Three is cope-able with on 2.5mm but if it was a 4mm ring might be no space?

You can only add 1 spur per socket on the ring. You can take what you like from that one spur because it's protected by a fuse. So you could spur off the ring with a double socket, but if you went via a FCU you could have 3 double sockets - protected by the 13A fuse in the FCU.

SPECIAL LOCATION · Nov 3, 2010

Have a look at the illustration on page 362 Appendix 15 of BS7671..

This gives example of arrangement of ring final circuits and connection of spurs.

The key point for consideration is are you reducing the cable size CSA, or spurring off with the same cable CSA..

Look at the two spur examples on the left and right side of the ring pg 362!

Guinness

Evans Electric · Nov 3, 2010

There may be reasons for the guy to be doing as he does. You say its kitchens you are doing , where you get the isolation problem of a socket hidden behind an appliance so no means of isolation.

A switched spur at worktop height solves the problem, he may be looking at that way.

You can take an unfused spur from the ring but mustn't overload the cable with a load of sockets, hence by fitting a spur unit the 13A fuse protects the spurred cable by limiting the load.

Some kitchens will have DP switches feeding a single socket behind a unit .

alchemist · Nov 3, 2010

Depends on the situation. If adding to the circuit that's arleady in place a spur is probably easier but if doing an entirely new circuit from 1st fix, include the FCUs in the ring.

The FCU is there to protect the flex on the appliance in the absence of a fused plug, all the other cabling is protected by the circuit's fuse/mcb.

I have a question...

When you have the FCU above the worktop, if you don't want to put a plug on the appliance (inevitably ending up with a fuse in a place that's hard to reach), what would you use to connect the appliance to the FCU? Is there something like a smaller version of a cooker outlet that goes on the wall to connect the flex into?

Sorry to hijack the thread, it just seemed relevant.

tom1 · Nov 3, 2010

Depends on the situation. If adding to the circuit that's arleady in place a spur is probably easier but if doing an entirely new circuit from 1st fix, include the FCUs in the ring. The FCU is there to protect the flex on the appliance in the absence of a fused plug, all the other cabling is protected by the circuit's fuse/mcb.

I have a question...

When you have the FCU above the worktop, if you don't want to put a plug on the appliance (inevitably ending up with a fuse in a place that's hard to reach), what would you use to connect the appliance to the FCU? Is there something like a smaller version of a cooker outlet that goes on the wall to connect the flex into?

Sorry to hijack the thread, it just seemed relevant.

flex outlet plate,