Burning cable, what should i do??

[moulton]

Every time I use my shower, I can smell a fishy smell coming from the shower switch (located) far away from the shower. I opened the switch up, and noticed some charring on the inside, and on some of the cable which runs from the fusebox. [This was installed professionally you understand].
So I replaced the switch, and the cable myself, using very heavy duty cable (cooker cable) but the burning smell has retuned. Does anyone know what's going on, help me please

 

[Steve]

Give us some sizes - rating of MCB/fuse, cable size (mm), rating of shower and switch, and switch type. Might be able to help then

 

[moulton]

Give us some sizes - rating of MCB/fuse, cable size (mm), rating of shower and switch, and switch type. Might be able to help then

Hiya Crafty, Thanks for the reply.
Right here goes:-

The Shower is a Triton T80 si (9.5w)
40amp fuse (from fusebox) switched.
45amp/250v switch [One of those with the big red light on it looks like a cooker switch]
and the cable, well, all i can make out of it is 2 x 6 - 2.5 sqmm??
I think that means, a 2 core cable with 2.5mm copper wires inside it.
Hope this helps Crafty, cheers.

 

[SwindonSpark]

moulton wrote:
the cable, well, all i can make out of it is 2 x 6 - 2.5 sqmm??
I think that means, a 2 core cable with 2.5mm copper wires inside it.

Is this the "heavy duty" cooker cable you mentioned earlier that is now installed?

Or is this the cable you removed?

 

[Big_Spark]

Moulton, that cable is too small by a long way, and a prime example of dodgy DIY.

That shower has a maximum load of 41.5A and as such should be fed by 10mm cable, not less. Some here may try to claim that 6mm will be good enough, but good enough gets people killed. The rating for 6mm is 32A so this will not do.

I would suggest that you stop messing about with it yourself, the fact that you thought this was cooker cables tells me that your not experienced enough to do this work, as such call in a professional spark.

 

[SwindonSpark]

I agree with FWL_Engineer.

10mm at least, not 6mm! Much better Iz figure.

Also worried about your 40A fuse ( In ) when your Ib figure is 41.5A

 

[Adam_151]

and the cable, well, all i can make out of it is 2 x 6 - 2.5 sqmm??
I think that means, a 2 core cable with 2.5mm copper wires inside it.
Hope this helps Crafty, cheers.

I guess it means 6mm cable with 2.5mm earth, that would make sense.

Oh and 6mm cable is not big enough (see FWL's post), but I wouldn't have thought it should have started melting, maybe get a bit too warm, give too big a volt drop to be spec, etc. but not melt, so that seems a little strange

 

[Steve]

I operated a 8.5KW shower on a 6mm cable and 32A MCB for about 6 years (not saying this is correct, i know its bordering on dangerous, but it worked), only when one of the connections started working loose did one of the cable ends start melting. I suggest you check all of your connections, in the fuse box, switch and shower, and if any are loose, you have found your problem. If not, dont use the shower and call a pro.

 

[Big_Spark]

Crafty, that is REALLY REALLY bad advice.

He has already indicated that he has a 9.5kW shower (41.5A) running on 2.5mm cable..loose connections are not the issue, the size of the damned cable is. It is way too small and likely to start a fire.

You may have got away with running 8.5kW (36.8A) from 6mm cable, that will fall into the upper range of what the cable is able to deal with in the type of installation you find in a home, but 41.5A is way above this upper limit and the ONLY solution is 10mm Cable.

Giving out advise that is advising someone who obviously has little knowledge of electrical systems to do something then ignore the underlying problem is fool hardy.

 

[delmel]

I would suggest always use 10mm covered then for future upgrades even if you had only a 7,2kw shower as i have. You mentioned it was fitted proffessionally.
was this an electrician or a plumber ?

 

[Big_Spark]

You mentioned it was fitted proffessionally.
was this an electrician or a plumber ?

Delmel. he may have been told it was fitted professionally, but as it is 2.5mm cable I find it difficult to believe that any professional would wire it in this cable. To be honest I would be surprised to this wired in this manner by a DIYer, except by one with no idea of what they are doing, but arrogant to ask or look in a book.

 

[Damocles]

If anyone cares to visit the TLC website and use their cable size calculator they will find that 6mm cable is ok for a run of 20m powering 9.5kw at 230V, PROVIDED the cable is laid where it has direct ventilation to cool it, so not enclosed in anything.

The most likely cause of this problem seems to be bad connections at the switch. The cable might or might not be overloaded but that is not going to cause localised heating just at the switch. It is not a cable problem which has been found here. If the cable is running in a loft, is it laid above the insulations.

Is any of this cable exposed anywhere so you can feel it after a shower and see if it has got warm?

While we are on the subject of safety, does anyone know just how great an overload current for how long a time a 6mm cable can carry? Cable is inherently cabable of carrying an overload because it starts off cold and takes time to heat up to working temperature. The calculations assume a cable is carrying that current constantly, which it is not. A shower might only be on for 5 minutes.

 

[Steve]

Crafty, that is REALLY REALLY bad advice.

He has already indicated that he has a 9.5kW shower (41.5A) running on 2.5mm cable..loose connections are not the issue, the size of the damned cable is. It is way too small and likely to start a fire.

You may have got away with running 8.5kW (36.8A) from 6mm cable, that will fall into the upper range of what the cable is able to deal with in the type of installation you find in a home, but 41.5A is way above this upper limit and the ONLY solution is 10mm Cable.

Giving out advise that is advising someone who obviously has little knowledge of electrical systems to do something then ignore the underlying problem is fool hardy.

I wasn't advising him, just telling my story.

I guess it means 6mm cable with 2.5mm earth, that would make sense.

Thought we were going along this line anyway. Sorry if i got my wires crossed.

 

[Big_Spark]

The most likely cause of this problem seems to be bad connections at the switch. The cable might or might not be overloaded but that is not going to cause localised heating just at the switch. It is not a cable problem which has been found here. If the cable is running in a loft, is it laid above the insulations.

Dam, we have already establish that the cable is 2.5mm NOT 6mm.

And as for you pointing out that 6mm can be used to supply more power if it is ventilated is about as much use as farting in a lift. Have you EVER seen perforated tray in a well ventilated area in a DOMESTIC premises..Nope, thought not, so there is no point mentioning it.

All this conjecture you guys are lobbing into this is getting away from the fact that this circuit is DANGEROUS AND NEEDS TO BE ATTENDED TO BY A PROFFESIONAL, someone that actually knows what they are doing.

OBTW..6mm T&E does not have a 2.5mm Earth core, it is and always as been 4.0mm. The designation on the cable mentions above is 6 stranded 2.5mm, which is OLD 2.5mm at that as all 2.5 mm is solid cored these days, and has been for over a decade.

 

[kai]

Modern 6.0.sq.mm. cable DOES have a solid 2.5.sq.mm earth, whilst 10.0.sq.mm cable has the stranded 4.0.sq.mm earth, that's the easiest way to tell them apart at a glance. Check in any cable manufacturer's website or catalogue dated after 2001.