melting cables!

[bri]

Can anyone explain some lighting problems im having.

About a week ago all the lights started flickering when turned on (on one of the upstairs circuits) and then 5 days later they all died on that circuit. When i checked the fuse box, the live wire insulation had melted just above the fuse, the fuse was still switched on and the RCD was still on?. There should be 6 lights in total on this circuit and a fan in the bathroom. 4 of the lights have 60W bulbs and 2 have 3x50W bulbs = 540W, i dont think this should overload the circuit?.

Bearing in mind that on the other upstairs circuit some of the lights stay on even when their fuse is switched of!, although they are all still working at present . In addition the 32 amp fuses also all have 2 live wires in them, is this OK as never seen it before in a fusebox?.

 

[plugwash]

bri almost all domestic sockets are wired on rings which return to the fuse box

if its a rewireable fuse then it's probablly the wrong fusewire
if its a cartrige fuse check it really is a fuse
if its a breaker then it's either seriously dodgy or the wrong rating

also sounds like you may have cross connections between cuircuits

an install in that kind of mess needs inspecting by a pro unless you are extremely knowlageable (which you obviously are not being unuable to recognise a ring)

 

[bri]

Thanks Plugwash, the 32A fuse question was just an additional query really, as i know what a ring circuit is...i was just unsure as to how safe having 4 wires going into one fuse is...that would suggest that there are two rings on one fuse?, which i dont think is right....i agree its a mess though.

As for the lighting circuit, i think there may be some cross-connections but as only one (of 2) upstairs light circuits is out and the circuit isnt overloaded (i think) i wondered if there could be any other causes for the problem of the wires overheating (short-circuit?) but cant see why the MCB hasnt tripped?

 

[dingbat]

Bri, as plugwash has suggested this sounds like one for the professionals. If you don't know what circuits are connected to each fuse why not call a local electrician to carry out a periodic test and inspection? If you have four conductors going into one fuse it sounds like the kind of installation I see every day - added to ad-hoc until nothig is being protected properly.

You may not like the conclusions and recommendations, but overloaded circuits may cost you much more in the long run.

 

[plugwash]

yeah a short is a very possible cause i think from what you have said now my initial idea of a cross conenction is fairly unlikely

2 rings on one breaker is a no-no

you need to use a continuity cheker to fins out which pairs of wires from the 4 are rings and seperate them

as for the breaker if it's the right rating then was probablly faulty

personally after a melting incident i would say the whole cuircuit should be replaced i wouldn't even bother faultfinding the old wireing (though check the accessories before reconneting to new wiring) because where there has been a melting! on part of the cuircuit other parts of it almost certainly have hidden damage

i presume 2 rings were put on a breaker because the box was full. Also if one mcb failed in a non safe way i would be suspicuos of the whole box and especially of other breakers of the same rating in there (what brand is it anyway) so a cu replacement may be in order.

a cu replacement isn't that hard but you must be very carefull to make your joins well. to isolate the cu the board may supply an isolator if not then you need to pull the service fuse (don't wory about breaking the seals)

it is ok to have lights on a ring but they must be fused down with a fcu fitted with a suitable fuse i guess the lights that don't turn off with eier upstirs lighting cuircuit are on the ring you need to trace theese and make sure they are suitablly fused

 

[Sym]

Bri - If you have melting by the fuse, you may also have melting further up in the wiring. I would definatly inspect it all or take it all out and start from scratch.

 

[Big_Spark]

A short is very unlikely to be the cause of the problem for a couple of reasons.

1) the circuit is MCB protected and this should trip with a short faster than any fuse ever will...

2) This is the most likely one to go, he said it has an RCD main switch, so if there was any inbalance on the circuit, whether Live-Neutral, Neutral-Earth or Live -Earth, the RCD would operate.

It might be one is U/S, but both is unlikely, so the chances of it being a short are very slim indeed.

Melting cables in the consumer unit, well there are a number of things that can be the cause..

1) Loose Termination resulting in arcing and heat generation.

2) MCB is faulty and causing heat build-up..rare bu no unheard of.

3) Overloaded circuit which is not enough to trip the breaker but enough to cause heat generation in the board.

4) Incorrect breaker rating or type fitted, coupled to overloaded circuit.


These are the most common causes for what your seeing, however as everyone above has pointed out, call a professional. The entire installation requires a FULL Test and Inspect with a full report written up. Remedial work to correct any problems should be high priority.

Your lighting problems suggest that there is a loose connection or duff MCB causing the problem, but the PTI will show this.

Regarding the lights staying on when the circuit is off....this should be cause for concern if we are talking about cieling mounted lights. If they are wall lights, then they may have been spured off the ring-main or even the downstairs lights, you'd be surprised what some people do in the name of saving money.

The most likely cause is that the two lights in question are wholly fed from another circuit, if there was a cross connection on the live side of the circuit then all your lights would stay on when the breaker was off as they would be double fed..like a ring but from two breakers..Having an RCD in place makes it unlikely that a neutral-live fault is the cause, though if the RCD is faulty it is not impossible.

I would like to say good luck, hope it isn't too expensive, but it does sound nastily like a rewire could be on the cards..of at least the upper floor lights anyway.

 

[bri]

thanks for all the advice, the problems have only occurred since an electrician installed new electrics to an extension on the house, i think he has used the existing board and fuses to add the new circuits to, since he has done the job there is a red 1mm (live?) cable loose in the box floating around which wasnt there before, so may have become disconnected or has just been left. Unfortunatly this electrician has been back twice and the problem seems to have got worse so i will have to find another one to check it all out

cheers Bri

 

[AdamW]

There is an assumption that has been made by all which hasn't been confirmed here: is the lighting circuit going through a 5A protection device?

This has spurred my suspicions that someone has incorrectly chopped around the electrics in the past:

Bearing in mind that on the other upstairs circuit some of the lights stay on even when their fuse is switched of

Thus it is not impossible that someone who has done this has spurred off a lighting circuit, and uprated the lighting fuse to cover this and is thus pulling too much current through the 1.5mm cables.

Perhaps you should get a tester, and try switching everything off except one circuit at a time and check everything you can!

 

[Big_Spark]

Thus it is not impossible that someone who has done this has spurred off a lighting circuit, and uprated the lighting fuse to cover this and is thus pulling too much current through the 1.5mm cables.

Adam, the fuse would need to be really big for that effect to be the case. 1.5mm Twin and E has a rating of up to 22A (depending on installation method) I have seen situations where 1.5mm Twin has been used to draw loads as high as 25A without damaging the cable.

It is unlikely a domestic lighting circuit will pull this much load.

I think two things we can all be in agreement on though are this, 1) Call in a Profeesional Electrical Contractor, 2) Don't call the one who did the work last time!

 

[AdamW]

Ah, but my point is: if there are lights that are not on the lighting circuit (as was suggested by the original post), then the same person who did that might have spurred off the lighting circuit to install some sockets or fcus in an act of unity with his european spark cousins... In which case these new sockets might be used now for more than the original lighting circuit was intended. Or possibly even there is one of those quartz bathroom heaters wired into a 13A fcu on a 1.5mm circuit. Now, there was no mention of a 5A fuse for the lighting circuit (although there was mention of 32A mcbs) which could mean that if my "what if?" is correct then whoever had done said work installed an uprated fuse to stop it blowing whenever they turned on their new bathroom heater.

A lot of what ifs, but there is no evidence here to the contrary!

I definitely agree that a pro needs to be called in here though, it sounds like a bit of a muddle.

 

[securespark]

In my exp, 4 conductors in a fuse/mcb means a ring plus two spurs...

 

[Big_Spark]

In my exp, 4 conductors in a fuse/mcb means a ring plus two spurs...

Simon, we're discussing a lighting circuit

 

[plugwash]

yes but the original poster mentioned his rings as well

either way of you find 4 conducotrs in a mcb you need to get a continuity tester (a multimeter will do) and find out which pairs if any are parts of the same ring and which if any are radials

then rings go on a 32A breaker and radials on a 20A breaker

 

[Big_Spark]

Aha, I just re-read it and your right Plug, he does mention rings.

I would advise him to look at changing his consumer unit. His concern is that a couple of rings may be on the same breaker as there is no room in it. Well as you should have about 20% empty space in a CU/DB, he clearly does not have that.

It might well be worthwhile him looking into upgrading and getting the whole installation checked at the same time.

It'll be cheaper to get all the work done at one time than piecemeal.