Discuss fused spur of a fused spur from ring main in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

n180

-
Reaction score
23
Hi guys,

whats the regs regarding fused spurs?

Is it ok to have, from the ring main, a fcu, feeding another fcu, feeding another fcu etc or is it only one fcu per socket like a normal spur?

I've got a fcu spur from the ring main for a fan in the bathroom. I need to fit in an electric radiator in the bathroom. I'm thinking of taking the feed for the radiator from the FCU spur of the fan. Will that be ok?

Thanks in advance.
 
Mate, have a look at APPENDIX 15 in your copy of BS7671, it give you pictorial and written explanation, quite simple to understand and the diagrams are self explanatory. But to answer some of your questions, a spur utilising a FCU is usually used when you need to supply, something that is or has low current requirement, the FCU is designed so that you can fuse down, although it does come with a 13Amp fuse already supplied.
 
Thanks pete. I don't have the big one yet as I'm still in college. But I looked at the on site guide and found a note in appendix H, page 183. It basically says the total number of fused spurs is unlimited.

So I take it, it's absolutley fine to have a fcu fed off a fcu fed of a fcu etc. the Radiator is only 250w so combined with the fan they wont even be pulling 2 amps, so it should all be fine, right?
 
Thanks pete. I don't have the big one yet as I'm still in college. But I looked at the on site guide and found a note in appendix H, page 183. It basically says the total number of fused spurs is unlimited.

So I take it, it's absolutley fine to have a fcu fed off a fcu fed of a fcu etc. the Radiator is only 250w so combined with the fan they wont even be pulling 2 amps, so it should all be fine, right?


No a fused spur is what it is what that means is, you can with a fused spur from the RFC as many times as you like, NOT from spur to spur.
 
Put a 13amp unswitched spur adjacent to the socket, then you can run whatever you like within reason from the outgoing or load side of that.
 
No a fused spur is what it is what that means is, you can with a fused spur from the RFC as many times as you like, NOT from spur to spur.

Oh right. I totally misunderstood the onsite guide. So basically a spur of a spur is never permitted, even if its fused.

I'll have to just stick in a juntion box in the ring cables under floorboard and get a fused spur off that.

Put a 13amp unswitched spur adjacent to the socket, then you can run whatever you like within reason from the outgoing or load side of that.


Correct me if i'm wrong dave, but what I think your saying here is, I can just stick in the cables for the fan and radiator in the same fcu as they are both low wattage? Is that right?
 
Oh right. I totally misunderstood the onsite guide. So basically a spur of a spur is never permitted, even if its fused.

I'll have to just stick in a juntion box in the ring cables under floorboard and get a fused spur off that.




Correct me if i'm wrong dave, but what I think your saying here is, I can just stick in the cables for the fan and radiator in the same fcu as they are both low wattage? Is that right?

Not really mate as both items should have their own means of isolation with appropriate fuse too. But from the initial FCU you can loop from the SFCU for the heater to another for the fan. If your initial spur from the ring is from under the floor make sure you use a MF connection box rated to at least 32a.
 
Not really mate as both items should have their own means of isolation with appropriate fuse too. But from the initial FCU you can loop from the SFCU for the heater to another for the fan. If your initial spur from the ring is from under the floor make sure you use a MF connection box rated to at least 32a.

Why 32A??
Any leg of a RFC only needs to be able to carry 20A.
So junction boxes can be rated the same.



Sent from my iPhone using Tapatalk
 
Just a thought but i know the regs says you cant feed more than one point from a ring but what is the difference between two 13 amp fcu and 1 twin socket especially if you are only putting small loads on them and fitting 3 amp fuses
 
Just a thought but i know the regs says you cant feed more than one point from a ring but what is the difference between two 13 amp fcu and 1 twin socket especially if you are only putting small loads on them and fitting 3 amp fuses

But if you put a 13a unswitched spur straight from the ring you can run 'unlimited' beyond that.
 
But if you put a 13a unswitched spur straight from the ring you can run 'unlimited' beyond that.
Yes i agree with you dave and that would be the way i would do it. It was just a an idea where the regs says you can't run two fsu from one point of a ring (total load 26 amps) but you can fit one twin socket (total load 26 amps)
 
a fcu fed off a fcu fed of a fcu etc.
a spur of a spur

You need to be clear how you describe this. If you mean loop in and out of the supply side of a string of FCUs, each supplying one load, then you are constructing a radial branched off a ring which is not permitted. I would tend to accept it where the loads are fixed and small and the FCUs all together, however it would be better to make them part of the ring.

The other scenario that I don't think you mean, but your description isn't clear, is whether it is acceptable to make a fused spur from a ring and feed the supply side of another FCU from the load side of the first, and so on. This is Dave's suggestion, which doesn't fall foul of the circuit layout as each FCU creates a 'new' circuit with its own characteristics. With 13A fuse in the first one and 3A in the second to fuse a light or fan down from the 13A fused spur, I would think it quite suitable, but you can't really cascade any further as the fuses can't be coordinated.
 
I’m not suggesting that the OP takes this post too literally but it’s interesting how readily we all comment about radials off a ring not being permitted. Being totally pedantic it’s not quite the right language. I’ve never found a reg saying that (look at 433.1.204 carefully). The appendix diagram seems to be the main guidance that is followed.
The main issue is that the person installing it can’t be in control of the loads for the lifetime of the installation so wise practise is not to run multiple socket points off a spur but I don’t believe it is explicitly prohibited.
Ducks for cover!
 
Just a thought but i know the regs says you cant feed more than one point from a ring but what is the difference between two 13 amp fcu and 1 twin socket especially if you are only putting small loads on them and fitting 3 amp fuses
I'd have said the regs do let you have more than one socket on a radial off the ring if the loads are known (though I accept it is rarely done, not widely understood to be the case and I've never done it), and there is therefore no difference if it is FCU's or sockets.
It's incredibly rare to see this done - I've seen it once in a hotel lobby with single floor sockets and a 40w table lamp on 4 tables, all on a spur of a RFC. It blew my mind at the time, but my conclusion was that it is allowed. Had they all been wired into FCU's that actually makes it safer as the loading is even more locked down.
 

Reply to fused spur of a fused spur from ring main in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock