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A lighting CB wont re-set and shower CB rating query.

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alw94

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I completed the wiring on an extension of some relatives of mine and certified it about 5 months ago. Now, the main part of the house has some old wiring and I have fixed, repaired and moved sockets and lights but I haven't carried out any testing on this side of the house. The extension wiring is mine from start to finish and is all checked out. I have just had a call to say that a week ago both RCDs tripped and that that since then the CB for downstairs lights won't re-set. Now, instead of phoning me, they contacted Southern Electric as they have one of those monthly service contracts. He has commented on the shower I fitted (9.5kw shower/10mm cable) being on a 50a CB. At the time I was looking for a 45a CB but, as far as I remember, Wyles don't do a 45a CB, so did a bit of checking and plumped for the 50a CB thinking that this and the 10mm cable would also allow for any changes in future. The guy from Southern Electric had to phone his boss who have recommended as 32a CB. This can't be right can it? Looking at other posts I think I'm on safe ground. Any comments from you folk?

Now, he hasn't checked anything else - actually, it's not clear at all just what he has done - but the downstairs lighting circuit still won't re-set. All I have done to this circuit before was to change a pendant and used this circuit for the smoke alarm in kitchen and hall. Considering that all was well for 5 months this problem has only occurred after both RCDs tripped. Could it be as simple are bulbs blown causing problems? I've asked them to switch all lights off, re-set CB and then go around switching on one room at a time but they are not even sure of some of the lights are on or off as they are dimmers. I live 200 miles away and they want me to go down to sort it out but am really pushed to find the time. Any helpful tips from you folks about assessing the possible problem before making the trip?

It, of course, is making me feel uneasy about whether I've done something wrong but short of not quite tightening wires up, I can't really see what. It doesn't help that it took 5 days for them to come to me. Instead they went to Southern Electric, an apprentice friend of their son and other people who all have a comment to make. When I first spoke to them they apparently had problems with sockets I fitted but I think we've got to the bottom of those and they are ok.
 
New installation added for the extension of the house. No previously installed circuits extended. What was in previous is still in unchanged apart from the d/s light which I connected the smoke alarms into that is all. New board fitted to 17th and tested. Basic checks first time (2yrs ago) met osg. I know I need to go back and find on what the problem is and a new set of results for all circuits is needed. To make sure and to cover old and new.
 
10.5KW...so thats 45.65A....so call it 46A.......your 10mm cable can carry 64A method c (clipped direct)....so in this case go for a 50A MCB...but check the install method first..(how the cable`s been run)...through insulation for instance as that will knock down the CCC..........
 
No, no insulation. It is a short run as the new bathroom on other side of the cupboard housing the board. Both are on the ground floor, so loft doesn't come into it. No insulation in ceiling above the bathroom. No grouping of cables either. I did consider all this and that is why plumped for the 50a. My mistake to confuse the issue by stating originally it was a 9.5kw. I guess the SE guy assumed it to be a 9.5kw thought too. Glenn, I appreciate you taking the time to even respond and check what I've done. I realise that I've sound like a real muppet and obviously can't go up against you guys for knowledge and wouldn't even try but apart from initial testing of the unchanged circuits I have been careful re the installation & testing afterwards. Full testing to be done on Friday to try and sort the tripping.
 
No, no insulation. It is a short run as the new bathroom on other side of the cupboard housing the board. Both are on the ground floor, so loft doesn't come into it. No insulation in ceiling above the bathroom. No grouping of cables either. I did consider all this and that is why plumped for the 50a. My mistake to confuse the issue by stating originally it was a 9.5kw. I guess the SE guy assumed it to be a 9.5kw thought too. Glenn, I appreciate you taking the time to even respond and check what I've done. I realise that I've sound like a real muppet and obviously can't go up against you guys for knowledge and wouldn't even try but apart from initial testing of the unchanged circuits I have been careful re the installation & testing afterwards. Full testing to be done on Friday to try and sort the tripping.
not a muppit mate and none of us know it all.....iam still green mate....just if altering circuits then inspection and then testing should follow....as for the cable run....your post didn`t mention about the method and any grouping so i was going a bit blind but in this case use a 50A...it will be ok although i suspect that this 10.5KW shower will not be used up to full potential and as such may not pull enough current to affect a 40A.........
 

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