Cooker/Grill is tripping only the lighting circuit

[Shep2013]

Hi there,

I am new to this but was wondering if anybody had any ideas..

When the oven and grill are both on they often seem to trip out the downstairs lighting circuit..

* The cooker is run on its own 10mm supply which does not trip out, but is on the same side of the consumer unit as the downstairs lighting.
* The downstairs lights are on their own 1.5mm radial consisting of 2 pendant lights, 2 sets of wall lights and 6 downlights in the kitchen (mixture of 50w halogen and 3/5wLEDs
*Nothing else trips out and it is only when the Grill and Oven are on at the same time
*The washing machine is also on (Downstairs ring and is still running)

Anybody have any ideas what could be happening??

Cheers

 

[Iggifer]

what's tripping then, the rcd? or the mcb for the lights?

If it's the RCD sounds like one of your elements could be failing and tripping the RCD.

 

[Shep2013]

Its the MCB for the lights - The RCD (also with the cooker on is not tripping

 

[Iggifer]

interesting. is this repeatable behaviour?

 

[Shep2013]

The house was completely rewired about 10months ago but it is only more recently I have noticed it happening.

3 times in last couple of weeks

Sometimes it will let you reset the MCB and it will go again within a couple of mins, other times it wont reset until you have finished cooking.

Luckily has been light every time so far so can finish cooking then reset!

 

[JohnW2]

When the oven and grill are both on they often seem to trip out the downstairs lighting circuit. [MCB]

Goodness. As I'm sure you realise, this is pretty extraordinary, verging on the totally bizarre - and, at first sight, it's very difficult to think of a possible explanation for what you describe (other than a complete c**k-up of the wiring! - an {obviously incorrect} connection between the two circuits could cause this to happen).

Does this happen regardless of whether any of the lights are on at the time? Has the oven/grill ever tripped the lighting MCB when none of the lights were switched on?

Kind Regards, John

 

[JohnW2]

...(other than a complete c**k-up of the wiring! - an {obviously incorrect} connection between the two circuits could cause this to happen).

You could test for a cross-connection. If, with the oven/grill off, you switch off the oven circuit MCB, then if you then attempt to switch the oven on, if there is a cross-connection,it will try to get all it's power via the lighting circuit and hopefully cause the lighting MCB to trip immediately. [if the oven comes on, with it's MCB 'off', and stays on for any appreciable period of time, then switch it off quick - because goodness knows where it would be getting its power from!]

Kind Regards, John

 

[Shep2013]

Hi John,

Thanks for your thoughts on this, I agree, it is very strange!

The cooker is definately getting it power only through its own 10mm supply but i tried it just in case and as soon as you turn its mcb off the display turns off.

I can be 100% sure that is no cross connection between the 2 after it leaves the consumer unit.

I am not an electrician but i personally rewired the whole house when i was renovating it (under the supervision of a qualified electrician who told me what cable to run and then checked it was all correct as i proceeded - 3visits and he then finally came back wired up a new consumer unit and tested it all and sent to BR. So i know exactly how it is wired (except the CU) if this helps.

I have just tried the oven and grill on max with no lights on and after about 3 min it has tripped the lighting circuit.

As i say i am not an electrician but have a grasp of the basic and am completed stumped by how this can possibly be happening!

Could it be anything to with the wiring in the CU? or would this not mean the cooker and RCD would short?

If it helps the cooker MCB says B40, does this mean 40Amp? And the lighting is B6

Thanks again

 

[Shep2013]

PS. The Cooker circuit runs down the wall and under the downstairs floor and the lighting circuit runs straight up under the upstairs floor so they dont go anywhere near each other

 

[flameport]

Probably a thermal effect - when the cooker is on the MCB for that will heat up, and the heat is sufficient to trip the adjacent lighting MCB (as it is of much lower rating than the cooker one).
Could be made worse by a loose connection for that MCB.

 

[Shep2013]

Probably a thermal effect - when the cooker is on the MCB for that will heat up, and the heat is sufficient to trip the adjacent lighting MCB (as it is of much lower rating than the cooker one).
Could be made worse by a loose connection for that MCB.

Hi Flameport

Thanks for your thoughts..

How would you suggest solving this then?

The Cooker MCB is next to the lighting MCB and upstairs sockets.

Would you swap its position to where the upstairs sockets are now? This would put it between the downstairs sockets and upstairs sockets (which are on the other RCD)Both are rated at 32 - as they have a higher rating any thermal effect wouldnt have as much of an impact?

Also is this something i can test? would it be a noticable heat coming from the ccoker MCB and is this normal?

Many Thanks

 

[JohnW2]

Probably a thermal effect - when the cooker is on the MCB for that will heat up, and the heat is sufficient to trip the adjacent lighting MCB (as it is of much lower rating than the cooker one).

I suppose that's possible, but I would have thought that one would have had to raise the temperature of the casing of a B6 (from outside) to a high enough temperature to melt it (or, at least, do thermal damage to it) before the MCB would operate (purely thermally) with absolutely no load on its circuit. I somehow doubt this is the explanation - but I may,of course, be wrong!

Could be made worse by a loose connection for that MCB.

That could certainly exacerbate any thermal things which were going on.

Shep2013: Is there any sign of either of the MCBs getting noticeably hot, or having suffered any thermal damage.

Kind Regards, John

 

[JohnW2]

The cooker is definately getting it power only through its own 10mm supply but i tried it just in case and as soon as you turn its mcb off the display turns off. I can be 100% sure that is no cross connection between the 2 after it leaves the consumer unit.

Right. If there is no cross-connection outside of the consumer unit (and no cross connection within the condumer unit), then that almost eliminates any 'electrical'explanations - leaving a 'thermal' one, such as suggested by flameport, as all I can currently think of (even if it does sound unlikely to me!)

I am not an electrician but i personally rewired the whole house ....

Nor am I - so no need to apologise or feel defensive about it

I have just tried the oven and grill on max with no lights on and after about 3 min it has tripped the lighting circuit.

That's pretty quick. If it were a thermal phenomenon with the MCBs, I would think that they'd both have to be getting pretty hot.

Could it be anything to with the wiring in the CU? or would this not mean the cooker and RCD would short?

A cross-connection between circuits within the CU could cause such a phenomenon, but if (as you say) the oven's lights go out when you switch off its MCB, that really rules out any cross-connection, anywhere.

If it helps the cooker MCB says B40, does this mean 40Amp? And the lighting is B6

Yes, B40 is 40A and B6 is 6A. The 'B' indicates how high a current overload (beyond the 40A or 6A) is needed for the MCB to trip 'immediately'. Type 'B' MCBs are the norm in domestic installations, with a very few exceptions.

I'll keep thinking!

Kind Regards, John

 

[viewer]

Are there any fans in the kitchen?

 

[JohnW2]

If there is no cross-connection outside of the consumer unit (and no cross connection within the condumer unit), then that almost eliminates any 'electrical'explanations - leaving a 'thermal' one, such as suggested by flameport, as all I can currently think of (even if it does sound unlikely to me!) .... I'll keep thinking!

I've thought a bit more!

There's a simple way in which you could eliminate (or not) all 'electrical' explanations, hence (as far as I can make out) leaving only flameport's 'thermal' one. .... temporarily disconnect the lighting circuit from the MCB, so that there is nothing connected to the load side of that MCB, but leaving the lighting MCB 'on'. Then try your oven+grill. If flameport is right, the lighting MCB should trip even though there is nothing connected to it.

Kind Regards, John