Help please!

[Prince1983]

Hi All,

I hope you guys are well and have had a good day!

its actually my first time on here and I was wondering if you could give me some advice please.

i wired up an oven with a cooker switch and then cooker outlet plate. Did the continuity test and insulation resistance test and everything was ok with results. I then switched the mcb on and everything was fine. I then switched on the cooker switch and the oven went bang!!! The RCD tripped but the MCB did not so looking for an earth fault. Then I disconnected everything. I did an insulation resistance test from the CU to the cooker switch and the readings were greater than 999M ohms. i then did an IR test from cooker switch to the outlet plate. everything was then also ok. i then did an IR test on the cooker lead and the earth to line reading was 0.26M ohms suowing an earth fault. I then connected from the Consumer Unit to the cooker switch and outlet plate without the cooker connected and everything was fine no trips. Could you please help me in deciphering this problem, thank you.

 

[billy badger]

Check the connection box on the oven. Many come with several connection options for different voltages and are supplied with links to fit as required. If wiring tests ok it sounds like the oven is incorrectly connected. If it went bang it's surprising that MCB did not trip.

 

[telectrix]

either that or a knackered oven.

 

[CrazyScozzese]

May just be a dodgy cooker. I had one straight out of the box with a live wire trapped between two panels once.

If you are careful with the metalwork, as a quick test you could put a plug on the cooker with a 3a or lower fuse if you have one, plug it into an RCD protected socket. If it pops without any heat turned on it is dodgy. If it pops the RCD when you blip on the heat same goes. The fuse will limit any damage. A 2 amp MCB is better for testing like this, but this type of testing is only for when you don't want to rip the new appliance open.

 

[Prince1983]

Thanks for your reply guys. I was thinking it would be the cooker but what threw me is that someone had wired the cooker with 2.5mm cable, but was working fine. But when I replaced it with a 6mm cable it blew! Any ideas?? Thanks.

 

[telectrix]

that last post suggests you've wired it wrong at the cooker. maybe a N-E reversal, or a live conductor shorting to E.

 

[GLENNSPARK]

Thanks for your reply guys. I was thinking it would be the cooker but what threw me is that someone had wired the cooker with 2.5mm cable, but was working fine. But when I replaced it with a 6mm cable it blew! Any ideas?? Thanks.

come on son...
i think you`v answered your own question...havn`t you...

 

[Darkwood]

As above ...It worked ok before you upgraded the cable and its now gone bang have you checked the new connections since...
Did you insulation test to the outlet plate i.e. with the cooker switch in the on position.
Have you screwed through the cable when putting the outlet cover on.
Have you checked your connection in the oven ... maybe the flex grip wasn't holding properly and as you pushed it back it pulled the core(s)out of its/their terminal(s).... etc etc

When you have done all the above then start your thread
Its seems a simple problem shouldn't be too hard to pin down.

 

[Prince1983]

Are you talking about the actual hob? Because I didn't wire that up. With my readings and with visual checks everything was wired as should be. Could it be that at the hob it is connected wrong as I have not yet checked it. The only other thing that I can think is that for some reason on the cooker outlet plate I put the line into the earth marking and earth marking into the line marking, but it was still line feed to line load and earth feed to earth load and neutral feed to neutral load. That should not affect it should it as essentially its just a junction box? Am I wrong.

 

[CrazyScozzese]

... if the live connected to the Earth 'marking' is connected to the earth of the back box.

 

[Prince1983]

No the back box was also connected to the earth at the live terminals...

 

[Darkwood]

Are you talking about the actual hob? Because I didn't wire that up. With my readings and with visual checks everything was wired as should be. Could it be that at the hob it is connected wrong as I have not yet checked it. The only other thing that I can think is that for some reason on the cooker outlet plate I put the line into the earth marking and earth marking into the line marking, but it was still line feed to line load and earth feed to earth load and neutral feed to neutral load. That should not affect it should it as essentially its just a junction box? Am I wrong.

OMG!!!! did you just say that.... why oh why if its marked up as earth its probably screwed to the metal bracket plate and dare i ask why on earth you would ignore the markings!!!

The earth terminal isn't usually isolated terminal its grounded down to the bracket on its fixing.

 

[Prince1983]

Thank you. I understand that was not the best thing to do but I immediately just took it as a connection box. I have now rectified that problem. But with the cooker flex into the the hob connection unit now reading at 0.26M ohms, is it safe to assume that the flex will need replacing and the rest of the hob will be ok or is it a case of having to buy a new hob? Your help is greatly appreciated and I still don't know why I did that, it was rather silly of me making that mistake.

 

[Darkwood]

If as i suggest this was the cause nothing will be damaged the fault was at the outlet plate and it was screwed down tight therefore their shouldn't be any damage cause except to your ego!

I going to be harsh here ....

Your profile states clearly on your qualifications - you have 2365, 17th Edition, Part P

Having these would mean you follow the BS7671 meaning you connect as indicated on the terminals so in essence you contravened the regs you follow and learned a valuable lesson i hope... i seriously hope your future posts merit a higher level of competence or expect to be bombarded with some demoralising comments .... yes we all have a blonde moment but try not to advertise it to hundreds of qualified sparkies in this case...

PS welcome to the forum :seeya:

 

[Prince1983]

Very blonde of me and I agree with you! And yes have definitely learnt a lesson! But where I am now confused is that the flex to the cooker is reading at at 0.26M ohms. Is that normal? And thanks for the welcome.