Spur off Double Socket.

[Mark328]

OK, but only do it if you really are confident and comfortable, and make sure that you don't 'touch anything'!

Yes - but, as I said, looking in the CU alone would not tell you for certain that it's a ring (it could be a radial with a ';branch' originating at the CU),but if there is only one wire connected to the fuse holder for that circuit,then it must be a radial.

What is the 'rating' of the fuse protecting the circuit concerned?

Kind Regards,John

30A but then who knows if that's the correct cartridge fuse, house is over 100 years old

 

[JohnW2]

30A but then who knows if that's the correct cartridge fuse, house is over 100 years old

Assuming that the circuit is wired in 2.5 mm² (rather than 4 mm²) cable, that would only be acceptable today if it were wired as a ring (20A, or possibly 25A, would be the maximum acceptable fuse size if it were a radial).

 

[Mark328]

I think it may be easier(and more importantly safer) to just extend the TV power cord and run that through the side of the chimney breast and into trunking (instead of the 2.5mm that currently goes from existing twin to single spur off behind the tv).

I would just change the faceplate to some sort of plate with a hole for the flex. Same for the fireplace flex, flex through hole already in side of chimney breast and both flex's can just be plugged into existing twin.

So best flex for extending tv power flex?

 

[sparkwright]

You don't need to know.
You fit the unswitched FCU where the existing twin is, and still keep the existing twin.

 

[Mark328]

All the replies have been greatly appreciated. So nice not to have the snobbery of not just employing an electrician, thank you.
One question I do have though is how can I plug in an 8 gang extension lead into the existing twin but when I want to add a twin spur off there is so many factors to take into account. I would of thought an 8 gang extension lead is a much bigger risk to the circuit.

Would I be correct in saying that this is ok as the 13a extension lead fuse protects the circuit so its ok?

If that is the case, why can I not just spur off the twin with an FCU and then onto a new twin regardless if the existing twin is a spur itself, surely the FCU would protect the existing spur twin.

Im more intersted in the rationale where you can seem to get away with murder via an extension lead!

 

[securespark]

My understanding has always been - only one unfused spur, from any point on the ring - as per @PrenticeBoyofDerry post.
.

The number of non-fused spurs should not exceed the number of sockets directly connected to the circuit.

 

[JohnW2]

One question I do have though is how can I plug in an 8 gang extension lead into the existing twin but when I want to add a twin spur off there is so many factors to take into account. I would of thought an 8 gang extension lead is a much bigger risk to the circuit.

It's not really much, if any, of a 'risk', since the 8-way (or even a hypothetical 80-way ) extension will have a 13A fuse in its plug (and maybe also in the extension), so actually can represent little more than a single item plugged in with a 13A plug [the 'catch' is that a 13A fuse will allow a lot more than 13A to flow, but in some senses, it "shouldn't"!)

Would I be correct in saying that this is ok as the 13a extension lead fuse protects the circuit so its ok?

As implied above, yes, OK.

If that is the case, why can I not just spur off the twin with an FCU and then onto a new twin regardless if the existing twin is a spur itself, surely the FCU would protect the existing spur twin.

As above, an N-way extension connected via a 13A fuse (in its plug) is no different from any single item with a 13A fuse in its plug which could be plugged in. A more questionable thing is why the guidance suggests that an unfused spur can only supply one single socket, whereas it can supply one double one!

It's perhaps worth pointing out that the restriction of an unfused spur to supplying one (single or double) socket exists in 'guidance' in the Appendix of the regs, as is not a 'regulatory requirement'. However, there is an issue as regards cable. If you use 2.5 mm² cable, since that would be adequate to supply,at most, 2 x 13A loads (hence, possibly, just one double socket). If you used 4mm² cable, I personally see no (electrical) reason why you could not supply at least one additional socket.

 

[Ragnar_AT]

You could pull the fuse, open sockets until you find one with two cables, disconnect the wires and then check for continuity between both reds, both blacks and both earths. If you get continuity on all three, it’s a ring, otherwise it‘s a radial or a broken ring. If it’s a ring, you could go with the fused connection unit. If it’s a radial you need to check the wire size and might need to reduce to a 20 A fuse.

How many rooms does the circuit supply? You might be able to go down to 20 amps even if it’s a ring if that’s enough power for your needs. That’s what electricians often do if rings are broken and can’t be fixed without bashing massive holes.

 

[JohnW2]

The number of non-fused spurs should not exceed the number of sockets directly connected to the circuit.

Your quoting the OSG again, but can you explain the electrical sense in that 'guidance'?

There's certainly nothing in BS7671 which says anything like that.

Indeed if anyone wanted to comply with that guidance but also wanted to have a lot of unfused spurs, they could simply install dozen or two additional (but actually 'unwanted') sockets - since I don't think that even the OSG limits the number of sockets one can have on a circuit, does it?

 

[Mark328]

Thanks all but too much hassle for the desired outcome. Will just run the flex through mini trunking and plug into existing twin. It's been emotional.

 

[securespark]

John

One wonders why any publication contains any information at all.

 

[JohnW2]

John, One wonders why any publication contains any information at all.

Well, specifically, onel certainly wonders why the OSG contains some of the 'information'/guidance that it does. For example, as I asked someone earlier, what do you think about ...

As a rule of thumb for rings, unfused spur lengths should not exceed 1/ 8 the cable length from the spur to the furthest point of the ring.

 

[securespark]

Some of the information that has appeared since the early days is labelled "rule of thumb".

The regs themselves are not perfect either, but what I do with the OSG is look for the associated reg numbers in the margin.

 

[Harry Bloomfield]

A more questionable thing is why the guidance suggests that an unfused spur can only supply one single socket, whereas it can supply one double one!

If you have the two single sockets, then the two could be widely separated. Two widely separated sockets, would be much more inclined to be used to maximum capacity - potentially a 3kw heater, plugged into each socket. Much less likely, is two 3kw heaters, plugged into one twin outlet, because they would be so close together.

I vaguely remember, back in the mists of time, that two single sockets were once allowed to be spurred off one location of a ring circuit???

 

[JohnW2]

Some of the information that has appeared since the early days is labelled "rule of thumb".

True in some cases, and that one alerts one to the fact that one may feel inclined to take the 'rule of thumb' with somewhat of a pinch of salt. That is true in terms of the sentence from the OSG I just quoted, but it is not true of the adjacent sentence which we started by discussing, namely ...

The total number of fused spurs is unlimited but the number of non-fused spurs is not to exceed the total number of socket-outlets and items of stationary equipment connected directly in the circuit.

The regs themselves are not perfect either, but what I do with the OSG is look for the associated reg numbers in the margin.

Indeed, and in relation to the two bits from the OSG which we have just discussed, we would not find an "associated reg numbers", since there aren't any