Tracing a spur

[Woodendhead]

While looking into where I could (or get a spark to) put a spur in for a TV loft amp, I discovered the logical point for an existing spur looks like it is part of a ring main or what I fear is spur on a spur.

Now I am beginning to worry about the wiring in this place.

I know how to confirm if it is a ring or the dreaded spur on a spur unless I have a damaged cable / broken ring, but any ideas on tracing the spur.

Also in my investigation I have found another spur I have no idea where this runs to, but as of tonight I do know it is not the known spur as I know they are on different rings. I had though I have traced the spur but no. Hence I am getting a bit worried.

The suspect spur on spur from the end I know about runs up into the between floors space, the socket that could be the is in the room / wall directly above hence my suspicions. The other runs down into the same space on the landing.

What I am not going to get away with is pulling floorboards up to trace these.

Thanks in advance for any ideas.

 

[Taylortwocities]

There's no easy way.

Look for a socket with three cables in the back of it
BUT
your spur could just as easily be fed from a junction box under the laminate/tiled/close carpeted floor

 

[ericmark]

The normal way is to disconnect at the consumer unit and connect the ring main cables line to neutral so one huge loop is formed. Then using a low ohm ohmmeter you measure the resistance line to neutral on each socket. All ring main sockets will have same reading. Non ring main sockets i.e. spurs will have a higher reading.

However although you can that way id ring or spur it does not really help curing the problem.

Easy cure is change the 32A MCB for a 20A MCB and in most cases this does not cause a problem. Some times where washing machines or other high amp items are on ring there is a problem.

 

[ajrobb]

It is possible that you have a radial circuit rather than a ring final circuit. (Most sparks now prefer radial circuits to ring final circuits.) A radial circuit in 2.5 mm² T+E cable will usually have a 20A MCB (or a 15A fuse) whereas a ring final circuit in the same cable will usually have a 32A MCB (or a 30A fuse). IF you have a radial circuit then there is no limit to the number of spurs off spurs you are allowed because they are actually branches.

What is the MCB or fuse rated at on the circuit in question?

 

[Woodendhead]

I am 99% sure it is a ring it has a 32A MCB and the house is the same age as myself.

I am sure my multi meter will not detect the resistance in the cables even the very expensive one I lost would have been beyond the sesitivity of the meter, I am electronics person to degree level.

 

[SparksElectrical]

No, it's not going to be much use. Sorry.

Easy enough to see if it's a ring or not, plug a socket tester into the socket, go back to the C/U and look for an MCB with 2 lines in it, turn it off, if the socket tester shows no power, you've found the ring. Simples.

As already said, it's possible but not a great idea to do that the spur could have been taken off a JB somewhere under the flooring. It does mean that testing is almost impossible if this has been done.

Can you not follow the cable back to the feed? Nothing obvious on other accessories? I've even seen sockets taken from lighting circuits so look there too.

It is permissible to have a spur from a spur so long they are fused and there's no more that 2 sockets. Neon fuse links aren't that expensive and will keep you within current regulations. Just make sure that it's not already spur from spur . . . . or even worse, from another circuit. I know the TV amp isn't much of a drain but do make sure that the circuit it's on isn't already at capacity?

 

[ban-all-sheds]

Woodendhead - one test you can do with a basic multimeter is this:

Having established that the socket is on that 32A MCB remove the line conductors from it and test for continuity between them. If you don't get it then it's a spur supplying another socket. (Or the ring is broken, but that's easy to check at the CU too).

If you do get continuity that won't show that you don't have a bizarre circuit, e.g. a figure of 8 or a bridged ring (but you can check for that by separating the conductors at the CU and seeing if the continuity at the socket remains), but at least it'll rule out the spur-from-a-spur scenario.

You might as well do the same checks for neutral and earth at the same time.

And in the bit-of-a-fag dept, take off every socket front to see if you do actually have any spurs...

 

[ban-all-sheds]

Easy enough to see if it's a ring or not, plug a socket tester into the socket, go back to the C/U and look for an MCB with 2 lines in it, turn it off, if the socket tester shows no power, you've found the ring. Simples.

No - not simples.

You'd see exactly the same behaviour if it were two radials or, depending on how the tester works, a partially broken ring.

 

[Woodendhead]

Looks like I am going to have to take sockets off, personally I don't like going in the CU and "mucking" about in it.

If I can't work it out myself, better to pay to get the spur put in, maybe get the CU inspected at the same time as that is due in a year or two anyway.

Just hope I don't break another dry wall back box doing the checking.

Thanks for the advice anyway.

 

[Taylortwocities]

If all you want is power in the loft for a TV amp then you can power it from the lighting circuit.
Just mark the socket as "TV amp only" so nobody plugs in a fan heater or use a 5amp round pin socket.

 

[holmslaw]

..

 

[Taylortwocities]

Yes, but (if you take the time to rad the thread) the OP has a problem trying to identify if the circuit he wants to spur from is, or is not, a spur already.

I was trying to offer a more simple alternative for him so he does not have to rip up his floorboards.

 

[holmslaw]

..

 

[Woodendhead]

Not considered that, is that within the regs plus if the amp ends up being powered via a switch mode with the plug all in one, I would need a 13A socket thus risk misuse (not by me), and FCU with a 3A fuse and a big warning would mitigate me a bit but not much.

Another solution is to get a mast head amp powered over the coax, then just put the power supply injector in the house.

 

[SparksElectrical]

Easy enough to see if it's a ring or not, plug a socket tester into the socket, go back to the C/U and look for an MCB with 2 lines in it, turn it off, if the socket tester shows no power, you've found the ring. Simples.

No - not simples.

You'd see exactly the same behaviour if it were two radials or, depending on how the tester works, a partially broken ring.

You'd only see 2 radials if they were taken from the same MCB surely? Fair point on the broken ring though.