H
holmslaw
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Dead shower, charred cable
- Thread starter CBX
- Start date
P
PrinceofDarkness
You've already made that most eloquent point, 'holmslaw'.
Are you the forum bully, by any chance?
Lucia.
Are you the forum bully, by any chance?
Lucia.
if you're refering to the link that BAS gave, that's the SI.. that's all it says and is the law..
your "additional notes" are most likely from the approved document? in which case they are useless as they are not what the law says at all..
K
kai
Shower pull switches can seem very unreliable at times, why can't you use a 60amp din-rail fitting main switch instead??, Note they are rated at AC22A duty, so they are designed for on-load use, and can safely switch the shower even if it's running (if you have kids about eh?) 
Ah bloody hell. Now I'm not even sure whether the cable is 6mm2 or 10mm2.
I was looking in a diy shed today at both 6 and 10 (though I'll probably not buy from there) - and the cross sections didn't look that much different. The 10 - although a larger total cable cross section circumference, didn't come anywhere near 10mm on either the live nor neutral. Maybe 7mm.
The copper stands looked slightly thicker than the 6 counterpart when compared side by side. Have I completely misunderstood how you are supposed to identify the existing cable size?
I was looking in a diy shed today at both 6 and 10 (though I'll probably not buy from there) - and the cross sections didn't look that much different. The 10 - although a larger total cable cross section circumference, didn't come anywhere near 10mm on either the live nor neutral. Maybe 7mm.
The copper stands looked slightly thicker than the 6 counterpart when compared side by side. Have I completely misunderstood how you are supposed to identify the existing cable size?
P
PrinceofDarkness
CBX: The size of a cable relates to its cross sectional area (pi r squared and all that). In the case of multi-wire (stranded) cables its the sum of the csa's of each strand.
Measurement of the overall circumference/diameter isn't always helpful, since manufacturing tolerances vary according to the age and quality.
As an approximate guide: the major sheath dimension of a 6mm T&E cable can vary between 12.5mm and 15mm, whereas a 10mm cable can vary between 15.5 and 19mm.
Given the size of your existing shower unit, either of those sizes will be adequate.
If you're going to poke around in your consumer unit, take care.
Lucia
Measurement of the overall circumference/diameter isn't always helpful, since manufacturing tolerances vary according to the age and quality.
As an approximate guide: the major sheath dimension of a 6mm T&E cable can vary between 12.5mm and 15mm, whereas a 10mm cable can vary between 15.5 and 19mm.
Given the size of your existing shower unit, either of those sizes will be adequate.
If you're going to poke around in your consumer unit, take care.
Lucia
Ah of course. If the diameter was 10mm, the cross sectional area would be 78mm2, or 50mm2 if only counting strand area. I knew I was missing something basic.
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Update, OK so my cable is 6mm2. Contrary to what I expected, it's actually the load side of the pull switch with the burnt Live cable. In the shower the cable is fine, and in the consumer unit (I was careful) the cable looks fine.
Presumably this points more towards a bad connection on the load side of the pull swtich rather than too much load for the cable etc?
I should point out that loft insulation has been put in recently by me, and although I was careful to lay insulation under the cable, and also treat it with care, I suppose it's possible moving the cable could have weakened the connection into the pull switch. Or it simply has been getting worse over the last 5 years.
I'm planning to renew the 2m section of cable to the shower, the pull switch (with an MK 45A one), and perhaps 5m of the supply cable as there's a little damage (not thermal) to the insulation about 30mm from the end and I'm not sure there's enough slack to cut it back.
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Update, OK so my cable is 6mm2. Contrary to what I expected, it's actually the load side of the pull switch with the burnt Live cable. In the shower the cable is fine, and in the consumer unit (I was careful) the cable looks fine.
Presumably this points more towards a bad connection on the load side of the pull swtich rather than too much load for the cable etc?
I should point out that loft insulation has been put in recently by me, and although I was careful to lay insulation under the cable, and also treat it with care, I suppose it's possible moving the cable could have weakened the connection into the pull switch. Or it simply has been getting worse over the last 5 years.
I'm planning to renew the 2m section of cable to the shower, the pull switch (with an MK 45A one), and perhaps 5m of the supply cable as there's a little damage (not thermal) to the insulation about 30mm from the end and I'm not sure there's enough slack to cut it back.
P
PrinceofDarkness
CBX: the supply side to the pull switch must be as taught as a banjo string if you can't manage a few inches of 'slack'. Have another look, you're bound to be able to tug a little somewhere along the route. Alternatively, you might be able to relocate the new switch by a few inches to gain some slack. It would be so much cheaper than replacing a certain length by using a joint-box - which in turn might also be a source of a loose joint.
That problem is bound to have been a loose connection at the switch terminal(s) - and nothing to do with your recent activity with the loft insulation. Such loose terminals create an awful amount of 'local' heat due to the arcing and sparking of the high-resistance joint.
Lucia.
That problem is bound to have been a loose connection at the switch terminal(s) - and nothing to do with your recent activity with the loft insulation. Such loose terminals create an awful amount of 'local' heat due to the arcing and sparking of the high-resistance joint.
Lucia.
Well I suppose the cables aren't that tight. I assume you mean try to pull the supply cable through enough for a little extra, but not the load cable which has been burnt (I'd never get enough through to cut back to be sure of good unoverheated copper).
However, given I'll have to buy some cable anyway, I thought I might as well buy 10m which should be enough for both pieces. I do understand about the extra joint concern - if it's needed I'll keep an eye on it (and the new pull switch) every so often to start with, and probably every 6 months in the future.
The shower episode has taught me a lesson. Don't just assume a registered sparky's work is perfect.
However, given I'll have to buy some cable anyway, I thought I might as well buy 10m which should be enough for both pieces. I do understand about the extra joint concern - if it's needed I'll keep an eye on it (and the new pull switch) every so often to start with, and probably every 6 months in the future.
The shower episode has taught me a lesson. Don't just assume a registered sparky's work is perfect.
The saga continues. After having bought some 6mm2 and removing the shower, I can now see the shower is labelled 9.6 - 10.5 Kw.
I'm guessing a 16m run of 6mm2 with this shower is a no no?
If so, pretty sh** that the electrician hired to do the job 5 years ago wired it in like that.
I'm guessing a 16m run of 6mm2 with this shower is a no no?
If so, pretty sh** that the electrician hired to do the job 5 years ago wired it in like that.
P
PrinceofDarkness
That's a nuisance, CBX. Do you know for certain that the original electrician wired to that particular shower - and not to a lesser rated one - since replaced? This happens frequently where a shower unit is upgraded but is still connected to the original circuit.
Whilst it's true that most electricians would naturally install 10mm for large showers, I don't see a great deal for you to be concerned about with your existing 6mm cable, even though it's right on its limit for current carrying capacity.
I wouldn't advise you to replace the cable to the consumer unit using the new 6mm cable - but I would advise you to carry on using the existing 6mm feed after trimming-back the terminations, since the damage was only due to local heat damage from loose terminals. In other words, if you were to replace like-for-like, those two 'wrongs' wouldn't make a 'right'. So carry out the simple repair/replacement of the shorter length - and ensure that your conections are sound.
Lucia.
Whilst it's true that most electricians would naturally install 10mm for large showers, I don't see a great deal for you to be concerned about with your existing 6mm cable, even though it's right on its limit for current carrying capacity.
I wouldn't advise you to replace the cable to the consumer unit using the new 6mm cable - but I would advise you to carry on using the existing 6mm feed after trimming-back the terminations, since the damage was only due to local heat damage from loose terminals. In other words, if you were to replace like-for-like, those two 'wrongs' wouldn't make a 'right'. So carry out the simple repair/replacement of the shorter length - and ensure that your conections are sound.
Lucia.
Presumably the ratings at 230V and 240V, so 42-44A.
It's borderline, but given the route you describe
6mm² would be just about OK, subject to it not getting much above 35°C in the loft, the airing cupboard or next to the hot pipes.
http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
But then you have to consider that the MCB should be replaced with a larger one, as the shower load is over 40A, which means the cable might need replacing anyway.
- http://www.diynot.com/forums/viewtopic.php?p=81696#81696
- http://www.tlc-direct.co.uk/Book/4.3.1.htm
- http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf[/list]
I'd say replace it with 10mm², or even 16mm², depending on what breaker sizes are available to you.
Yup.
P
PrinceofDarkness
CBX: stick with the devil that you know. Your MCB might have a slight 5% over-current through it, but it isn't an excessive amount - and it certainly isn't a constant '24/7' load.
I prefer to design a circuit so that the MCB is carrying 80% of its nominal rating. However, with existing circuits loaded to the hilt - but for a short period, I make practical allowances rather than going by a theoretical text book.
The very thought of someone using 16mm cable (as mentioned above) for a domestic shower, is ludicrous.
Lucia.
I prefer to design a circuit so that the MCB is carrying 80% of its nominal rating. However, with existing circuits loaded to the hilt - but for a short period, I make practical allowances rather than going by a theoretical text book.
The very thought of someone using 16mm cable (as mentioned above) for a domestic shower, is ludicrous.
Lucia.
H
holmslaw
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