srobrien Posted November 18, 2011 Share Posted November 18, 2011 Hello all you electrical type people.. Right I have an electric shower over the bath in our new house. I am looking at relocation the fused switch in the hall. When I took the faceplate off I noticed that the live incoming wire was blackened at the end and there was verdigris in the core. What could have caused this? The shower has been running for ages with no problems and would never have noticed this if I had never taken the facia off. Anything to worry about? Cheers R Quote Link to comment Share on other sites More sharing options...
AK350Z Posted November 18, 2011 Share Posted November 18, 2011 Looks like its got damp and arced or overheated. how many KW is your shower? cable size looks about right, but hard to tell from the pic. IMO it shouldn't be passing through a fused spur at all, It should be fed straight from a dedicated MCB with RCD protection. edit: also your back box is not earthed! Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 18, 2011 Author Share Posted November 18, 2011 Hi yeah the live comes from dedicated RCD first. Not sure on KW as I never installed the shower. It's a triton excite so should be about 8.5? Quote Link to comment Share on other sites More sharing options...
ChrisS Posted November 18, 2011 Share Posted November 18, 2011 As Andy says,looks like damp got in. Noticed the wallpaper has been stripped, so if that was done a while back that's probably it. Quote Link to comment Share on other sites More sharing options...
AK350Z Posted November 18, 2011 Share Posted November 18, 2011 Maybe down to bad contact or loosening in the back of the switch, either way, it needs remade at the very least. It's a double pole switch, which is fine, but is it really fused too? Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 18, 2011 Author Share Posted November 18, 2011 Cheers chaps looks like an old wound so will redress the cable and keep an eye on it. Oh and I'm an idiot it's not a fused switch just one with a wee light on it. R Quote Link to comment Share on other sites More sharing options...
Beavis Posted November 18, 2011 Share Posted November 18, 2011 That does not look like a fused spur to me, more like a double pole switch of approx 30-40 Amps. It looks like the connection was a little loose in the first place causing the cable to heat up. Re-make the cable off if you can and get a new switch. I assume this is located outside of the shower? Really it should be and certainly out of reach if standing in the shower! If it as a rating of 8.5kw 6mm cable will be fine above 9.5kw and above and then we end up moving into 10mm territory. Make sure that back-box gets earthed also. Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 18, 2011 Author Share Posted November 18, 2011 Damn that's where the moisture issue is coming from!! Haha. You are correct it's just a switch. R Quote Link to comment Share on other sites More sharing options...
AK350Z Posted November 18, 2011 Share Posted November 18, 2011 If you can't pull any extra slack on that cable it will need to be replaced For 8.5kw I would recommend 10mm2 depending on the cable run. That does not look like a fused spur to me, more like a double pole switch of approx 30-40 Amps. It looks like the connection was a little loose in the first place causing the cable to heat up. Re-make the cable off if you can and get a new switch. I assume this is located outside of the shower? Really it should be and certainly out of reach if standing in the shower! If it as a rating of 8.5kw 6mm cable will be fine above 9.5kw and then we end up moving into 10mm territory. Make sure that back-box gets earthed also. Great minds and all that... Had a quick google, and they do make a 9.5kw version of that shower. Plus i'd be temped to future proof it if the cable ends up being replaced. Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 18, 2011 Author Share Posted November 18, 2011 Sweet thanks for the help. I am moving it to the other side of the wall in a cupboard. The electric shower will be removed next year and the hall is getting plastered next week so want rid of all unwanted boxes and switches. Thanks all for the assistance R Quote Link to comment Share on other sites More sharing options...
Stew Posted November 18, 2011 Share Posted November 18, 2011 If you need Sparky help Ross give me a shout, My old man is a sparky to trade and he often has lots of supplies lying about. He also has a lot of buying power at the wholesalers so can get stuff (even showers etc) at reasonable money. Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 18, 2011 Author Share Posted November 18, 2011 Cheers mannie need to pop over and catch up soon Quote Link to comment Share on other sites More sharing options...
Zugara Posted November 18, 2011 Share Posted November 18, 2011 This is caused by an inferior connection only, high amps at the connection point = burning. Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 18, 2011 Author Share Posted November 18, 2011 This is caused by an inferior connection only, high amps at the connection point = burning. Thanks Pal, connection will be getting remade tomorrow. R Quote Link to comment Share on other sites More sharing options...
leonk Posted November 18, 2011 Share Posted November 18, 2011 Beavis said.. Make sure that back-box gets earthed also. and get some rubber grommets for where the cable comes through the metal box Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 19, 2011 Author Share Posted November 19, 2011 Right had the box off the wall again this morning, the switch was getting quite hot during use and there was a strange fishy smell which I can only assume is melting insulation. The shower is 8.7-9.5 kW The switch is 45amp DP and its MCB says 63amp on it so assume that's maximum load. The cable is 6mm Does this sound ok? Im gonna change the switch and backbox out today and redress the burnt cables. Hopefully solve the issue, R Quote Link to comment Share on other sites More sharing options...
Beavis Posted November 19, 2011 Share Posted November 19, 2011 Right had the box off the wall again this morning, the switch was getting quite hot during use and there was a strange fishy smell which I can only assume is melting insulation. The shower is 8.7-9.5 kW The switch is 45amp DP and its MCB says 63amp on it so assume that's maximum load. The cable is 6mm Does this sound ok? Im gonna change the switch and backbox out today and redress the burnt cables. Hopefully solve the issue, R You have problems!! 63 amp breaker? 1. The current rating of 9.5kw will draw approx 41 amps so you need a MCB no bigger than 45 amps. Remember the breaker or fuse is there to protect the cable and not the appliance. A 63 amp breaker will not be protecting a 6mm cable! 2. 6mm cable as a maximum cable rating of approx 38 amps so really its undersize (just) for that current rating of shower been used. 3. For now you need to replace the switch its f@cked and you really need to ditch the 63 amp breaker and downsize it to a 45 amp max breaker. (this will at least give the 6mm cable better protection for now) 4. In the long term though you need to get the cable replaced and upgraded to 10mm, if you can do it now then great. Quote Link to comment Share on other sites More sharing options...
MK-Ultra Posted November 19, 2011 Share Posted November 19, 2011 Hi mate, it depends on how the cable is run. i.e is it in conduit in the wall, does the wall have insulation in it? These factor can contribute to what size cable you need. If your shower has a max power of 9500Watts it will be pulling 41Amps. According to BS7671 the wiring regs, the current carring capacity of 6mm cable in a stud wall were the cable IS NOT touching the inner wall surface is only 23.5AMPS, and were IT IS touching is still only 35AMPS. So it looks as thou your cable is under sized It may need changing for a bigger size i.e 10mm. Which could well be a pain depending on how far the run is. The switch is the correct rating , but your MCB will need down sizing to protect the cable. This is why you may not have noticed any problems, even thou your cable is undersized and your shower is pulling too much power it still wasnt enough to trip the MCB. Edit: just seen Beavis' reply Quote Link to comment Share on other sites More sharing options...
Beavis Posted November 19, 2011 Share Posted November 19, 2011 Edit: just seen Beavis' reply At least we are singing from the same hymn sheet Quote Link to comment Share on other sites More sharing options...
MK-Ultra Posted November 19, 2011 Share Posted November 19, 2011 Edit: just seen Beavis' reply At least we are singing from the same hymn sheet True!! Must remember sometimes there is a reason when you click submit it doesnt post first time Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 19, 2011 Author Share Posted November 19, 2011 Goddamnit sometimes I really want to just punt the previous owner in the stones!!! I will post up a pic of the mcb when I get home to confirm. R Quote Link to comment Share on other sites More sharing options...
leonk Posted November 19, 2011 Share Posted November 19, 2011 I'm sure your'e not but make sure you are not looking at the main incomer which will be rated at 63A rather than the individual MCB which is protecting the shower circuit. That should be 40A Awaiting picture. Quote Link to comment Share on other sites More sharing options...
Ebized Posted November 19, 2011 Share Posted November 19, 2011 Edit: just seen Beavis' reply At least we are singing from the same hymn sheet No 'resistors' this time then Quote Link to comment Share on other sites More sharing options...
srobrien Posted November 19, 2011 Author Share Posted November 19, 2011 I'm sure your'e not but make sure you are not looking at the main incomer which will be rated at 63A rather than the individual MCB which is protecting the shower circuit. That should be 40A Awaiting picture. You might be on to something there im a total idiot. its on a board seperate from the main fuse box, and it has 3 switches. One says 63amp but can't see a rating on the others. I'm not a sparky I know enough to get by but when it comes to fuse boxes and load ratings I'm lost. It's a black art to me. Give me a bucket of oil any day. Haha. Here is a pic: Quote Link to comment Share on other sites More sharing options...
MK-Ultra Posted November 19, 2011 Share Posted November 19, 2011 Ok, yeah that 63amp is the main switch the smaller one is for the circuit. It would appear the space to the left of the 40 amp breaker is blank/spare. As previously said that shower is drawing too much current for your cable size. I would recommend changing that cable to a 10mm. In the mean time if you can pull enough of your existing cable into that switch point, you could re-make that connection in the switch. Just make sure you strip enough of the cable back till you can see bright copper. i.e it isnt black/damaged. Also for the sake of a few pound get yourself a new switch. That is a temporary solution, as i said i would recommmed changing that cable. Hope this helps. Quote Link to comment Share on other sites More sharing options...
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