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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.
 
manufacturers like to exagerate the current draw of their appliances.....same for cookers n all....hence your diversity you can apply....first 10A then 30% of anythin left...unless using a cooker with a socket built in then you add 5A...seeemples.....
 
Checked a 10.5kW shower the other day and it was pulling 43A and on a 40A rcbo with 10mm cable. mcb was warmish (only just so prob anout 40 degrees) after running for approx 20min. I guess it would be better on a 45 or 50A rcbo but that was on full hot for more than normal so I decided to ok it.
 
Checked a 10.5kW shower the other day and it was pulling 43A and on a 40A rcbo with 10mm cable. mcb was warmish (only just so prob anout 40 degrees) after running for approx 20min. I guess it would be better on a 45 or 50A rcbo but that was on full hot for more than normal so I decided to ok it.
well under normal operating conditions...cant see the users turning it up full.....and burning themselves....this is the thing....you get people wanting these showers with crazy outputs and they never get anyware near there full potential...mad innit.......
 
Cheers for the quick replies. I need to check it was a 9.5kw because something made me go up to the 50a rather than the 40a. It may be that it was a 10.5 but I haven't got my notes to hand. If I phone them they won't know either. I used this for my assessment and nothing was mentioned then.

Any tips on the lighting circuit as, if I have to go, it'll have to be done in a day, as I haven't the time to stay longer. Not looking forward to this as it's a 5am start and won't get back to 9-10pm depending on what needs to be done.
 
Cheers for the quick replies. I need to check it was a 9.5kw because something made me go up to the 50a rather than the 40a. It may be that it was a 10.5 but I haven't got my notes to hand. If I phone them they won't know either. I used this for my assessment and nothing was mentioned then.

Any tips on the lighting circuit as, if I have to go, it'll have to be done in a day, as I haven't the time to stay longer. Not looking forward to this as it's a 5am start and won't get back to 9-10pm depending on what needs to be done.
so did you ask the inevitable question.."have you had any work done sinse i was here last"?.....IR mate on the offending circuit......at the board first to verefy theres either a short circuit or a breakdown in insulation and remember to disconnect anything electronic being fed from this circuit first wont you mate as you could fry it..lol....
 
then if/when you have verefied theres an IR problem then you can seperate the circuit at the various points on the string......till you find the portion thats causing it....test strappers in both directions wont you n all as it may be something they`v hammered into the wall...hanging pictures or whatever..lol.....
 
10mm twin and earth depending on the installation method ie clipped direct can be rated at 63 amps check the current capability of the cable in the way that it's installed a 50 amp breaker may be fine, regardless of the power of the shower being less
 
Cheers. You wouldn't believe some of the problems I've had with the builder they used removing parts of the circuit and plasterboarding over switches! I'm always that last to know about problems and I spent half my time fixing bits and pieces for them instead of installing the testing the extension. There is always something else. Oh yeah, what about them removing sockets and leaving earth off...and neutrals...and a live! I had to quickly fix one ring main before my assessment. Not a good start. It's been a proper pain in the arse. Ferking family...
 
10mm twin and earth depending on the installation method ie clipped direct can be rated at 63 amps check the current capability of the cable in the way that it's installed a 50 amp breaker may be fine, regardless of the power of the shower being less
indeed but if you cant verefy the installation method for the whole run......better to err on the side of safety here and as has been mentioned here already....noware near the actual current draw.....40A good......
 
indeed but if you cant verefy the installation method for the whole run......better to err on the side of safety here and as has been mentioned here already....noware near the actual current draw.....40A good......

Yeah I agree, but what I was getting at was southern electric pointing out this as wrong... Could be completely fine and I'm sure the op would have checked the installed cable or actually installed it before putting on a 50amp
 
Cheers. You wouldn't believe some of the problems I've had with the builder they used removing parts of the circuit and plasterboarding over switches! I'm always that last to know about problems and I spent half my time fixing bits and pieces for them instead of installing the testing the extension. There is always something else. Oh yeah, what about them removing sockets and leaving earth off...and neutrals...and a live! I had to quickly fix one ring main before my assessment. Not a good start. It's been a proper pain in the arse. Ferking family...
well the point here is you identified 1s and dealt with em then didn`t you...
 
Prior to starting I did the ze & zs on the system but didn't check the individual circuits. The changes I made to the main house was new pendants, socket, moved socket & cooker switch from directly above cooker. I haven't extended or anything. I get it though - full checking would've highlighted possible problem areas. I'm just ****ed at having to go at short-notice to fix it when if they had told me I could've gone at the weekend. I still would've been ****ed but it would've been better timing. The lack of notice has been a feature though as whenever the builder has been plastering, removing switches etc I'll turn up and they'll tell me something somewhere is not working. I'll try and sort it before getting on with what I'm there for. How about the guy rendering around the lights and sockets outside instead of removing and re-fitting? Anyway, moan over. I'm just tried to help them.

I've checked my notes and went for the 50a as it is a 10.5kw shower. I fitted the the shower installation and it is clipped direct but didn't think there was any diversity allowed on a shower. Which is why plumped for the 50a. I get the full power not being likely for too long.
 
what book you using for you max Zs tables?...osg?...brb/bgb?.......as their both different.....one of em need a correction factor appled.....and this could affect whether the circuit Zs values obtained complied or not.......
 

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