Cooker Circuit

[Ewan32]

Hi everyone,

I have just joined the forum as I'm sure someone may be able to help with a strange problem I'm having with the cooker at home.

Many years ago I did an apprenticeship with British Steel as an Automation Technician and that involved quite some time on domestic and industrial electrical.  Since then I moved into IT and Computing so I'm a little rusty with the heavier stuff

OK, the problem I have is that recently the Bosch Hob and Oven setup we use has intermittently started playing up and power is lost to both the hob and oven - even the neon on the isolating switch goes off but the circuit breaker doesn't trip (its still in the up position).

I have pulled out the oven and see the mains wiring comes from the cooker switch to the oven and then in parallel up to the hob.

If I leave everything untouched for about 3 hours the power returns on its own (flashing clock etc).

I had a guy out to check over the cooker and hob but when he arrived (like going to the dentist with toothache) it worked fine and he could find nothing wrong.

It has worked fine since last Saturday until last night when I was using 2 rings on the hob and then it went off again - no power to the hob ; no power to the oven (clock display off) ; no neon lit on the cooker switch BUT the circuit breaker still in the up (active) position.

I have checked the cooker switch but all the connections seem to be OK, nothing loose.

Is it possible the circuit breaker itself is faulty as I would have thought if it were the oven or hob drawing excessive current it would trip the breaker properly ?

Why should the power restore itself without anyone touching anything after being off for about 3 hours or so ?

Any and all constructive suggestions /  advice gratefully received.

Many thanks

Ewan

 

[Andy™]

id start with checking the switch

 

[Doc Hudson]

Id also check the connections at the consumer unit for any loose terminals. Is the breaker correctly secured onto the live bar, is the neutral secured in the neutral bar. Continuity and IR tests down the cable as well wouldn't be a waste of time.

Doc H.

 

[ProDave]

Look for anything that has the slightest hint of getting hot. a poor contact, which is almost certainly what you have, will result in things getting hot.

I would have expected the electrician to have checked that the mcb is clamped to the busbar correctly.

Since it's hard to get someone there when it's actually gone faulty, I would start with replacing the switch and double checking the mcb connections.

 

[Evans Electric]

Both the above posts need checking out Ewan .

I too am thinking loose connection which could be , as Andy & the Doc have said :-

MCB busbar connection loose

MCB cable connection loose

The Double pole switch , loose connection

The splitter box loose connection 

Without a load the timer etc probably work until you switch rings on .

You need a mains tester but we cannot encourage you to start messing with electrics unless you are competent enough .

Look for anything that has the slightest hint of getting hot. a poor contact, which is almost certainly what you have, will result in things getting hot.

I would have expected the electrician to have checked that the mcb is clamped to the busbar correctly.

Since it's hard to get someone there when it's actually gone faulty, I would start with replacing the switch and double checking the mcb connections.

So would I  Dave but I wouldn't bank on it .. 

 

[Ewan32]

OK thanks guys.

We've lived in this place for 8 years or so and never had any problem with the cooker previously and the fact the MCB isn't tripping is what's puzzling me.

So just a few more questions if you don't mind ?

Would the cooker switch just fail - it rarely (if ever  gets used just stays in the ON position and its located inside a cupboard - no there isn't anything hitting the switch,  I've emptied the cupboard as that was my first thought .

How easy / difficult is it to replace the MCB, is it a case of removing the cover and releasing 2 screws and what are the chances of the MCB being faulty ?

Why would it all "reset" itself after a few hours ?

Cheers for the help lads, appreciated !

 

[Andy™]

switches do fail, either loose connection thats burns out or the switch contact. common failure, more so on showers

MCB's are there to detect overload and fault current. they are not designed to detect a faulty contact thats gone open circuit

 

[roys]

Switches do just fail, cooker circuit = plenty of current = plenty of heat especially if something is not quite right like a slack connection on dirty contact on the switch.

Easy to change a MCB if you know what you are doing (competent), power off, source correct replacement, fit replacement, tighten screws to correct torque.

Reset itself, probably to do with it cooling back down and when it cools down the resistance lowers and it is all OK again for a short while.

So it summary and as said above, it needs all the connections checked, if they are OK you want to be looking at changing the switch and / or the MCB. Must state only do this if you are competent to do it, don't want you getting hurt.

 

[Ewan32]

Many thanks gentlemen.

I really do appreciate your suggestions which I'll investigate further over the weekend.

Regards

 

[kerching]

Any weird smells of "fish" when the oven fails?a lot of accessories smell,fishy when they get very hot.

As said before....my money is on a loose connection

Just saying

 

[Murdoch]

Look for anything that has the slightest hint of getting hot. a poor contact, which is almost certainly what you have, will result in things getting hot.

I would have expected the electrician to have checked that the mcb is clamped to the busbar correctly.

Since it's hard to get someone there when it's actually gone faulty, I would start with replacing the switch and double checking the mcb connections.

He said he had somebody to look at the appliances not the circuit........ I've got a client with 2 perfectly good dishwashers because an appliance repair man didn't realise that the socket was knackered and the neutral had failed!

 

[Evans Electric]

Ewan you seem to be focused on the MCB  is there a reason for that ?

Did you take the switch plate off to check it ,  like shower switches , they can & do fail , either cheapo makes or loose connections. 

 

[Rob_the_rich]

it does sound like a loose connection at, or upstream of, the cooker switch.

Switch off at the main switch on the CU before opening the cover. check the terminals as above. Assume everything is still live unless you can prove it is dead, don't touch anything, including screwdriver shaft or bare ends of wires. There is a risk involved here and if you are unsure of what you are doing, please don't do it and get someone in.

What rating of mcb is it for the circuit?

What ratings are all the other mcbs?

I am thinking of swapping the mcb with one from another circuit of the same rating, or swapping the wires, but we need more information about what all your circuits are and if there are RCDs present. A photo would be great too, but I don't think you have enough posts yet to upload it to the forum, a moderator might help you there.

 

[Ewan32]

Hi all,

I have to go away until end of the week on a business trip but when I get back I'll start investigating.

Perhaps I'm totally wrong but the reason I suspect the MCB is because it remains in the ON position even when the power to the cooker switch is interrupted (i.e. Neon goes out). I don't think it can be a problem related to physical wiring because if left alone for a few hours and without me touching anything, the power comes back on by itself - neon lights on cooker switch and clock flashes on the oven.

Seems to work again then for a few hours / days and then the problem starts over again. As I said before, we've been here 8 years or so and never had a problem with it before - just suddenly started happening week last Tuesday !.

I thinks its going to be a case of disconnect oven and just use hob on its own to start with and see what happens.

Cheers for all the suggestions / support - most appreciated !

 

[Lurch]

What make is the CU/MCB.

 

[Andy™]

Perhaps I'm totally wrong but the reason I suspect the MCB is because it remains in the ON position even when the power to the cooker switch is interrupted (i.e. Neon goes out). I don't think it can be a problem related to physical wiring because if left alone for a few hours and without me touching anything, the power comes back on by itself - neon lights on cooker switch and clock flashes on the oven.

!

just ignore post 7 then, its not as if i have an almost identical problem at least once a month and its almost always the switch thats at fault and not the MCB

 

[ProDave]

Hi all,

I have to go away until end of the week on a business trip but when I get back I'll start investigating.

Perhaps I'm totally wrong but the reason I suspect the MCB is because it remains in the ON position even when the power to the cooker switch is interrupted (i.e. Neon goes out). I don't think it can be a problem related to physical wiring because if left alone for a few hours and without me touching anything, the power comes back on by itself - neon lights on cooker switch and clock flashes on the oven.

Seems to work again then for a few hours / days and then the problem starts over again. As I said before, we've been here 8 years or so and never had a problem with it before - just suddenly started happening week last Tuesday !.

I thinks its going to be a case of disconnect oven and just use hob on its own to start with and see what happens.

Cheers for all the suggestions / support - most appreciated !

Think this through.

If the NEON goes out, it means there is NO POWER getting to the hob and the oven.

So it WON'T be a fault with the hob or the oven, so disconnecting one of them will not prove anything.

It has to be the switch or the MCB. If you don,t want to pay someone for hours of diagnosis, then just pay someone to change the switch and the MCB.

As has already been stated now at least twice, the function of an mcb is to turn off in the event of over current (a fault). If as we suspect you have a faulty switch that's going open circuit, why would you think the mcb will trip.  With your fault no current will flow so the mcb can't possibly turn off.

Feel free to ignore the advice given, we like wasting our time.

 

[Essex1]

This is less than an hours work for a sparky mate.

 

[Sharpend]

This is less than an hours work for a sparky mate.

Yes but is he qualified? The sparky mate that is!

 

[Essex1]

Yes but is he qualified? The sparky mate that is!

Grrrrrrr!