New Oven tripping mcb massively

[Misterbarlow]

Hi everyone, stumbled across your forum while googling tonight, hoping for a bit of advice...
I have some electrical knowledge, and I fit/change electric meters for a living for past 20yrs for one of the big six!

Have been given a brand new (but faulty) oven by a relative, an Electrolux EOB3400EAX.
They got it brand new, don't know from where, cant find it on many websites, must have got it online??

The person who gave it to me said they got few days before Christmas and hadn't used it, as it was tripping out their electric from the off, and they were worrying about Christmas lunch failing etc as had lot of family coming over, they just thought it was too much for their wiring or mcb, so they just got another oven for Christmas which worked ok, and so this one been sat in the garage, and easy come for some, they couldn't be bothered sending it back so they asked if I wanted??

My prev oven been in use about 8yrs, no issues, wiring all good and up to scratch here..

So. wired it up, turned on, all seemed ok, turned the dual element oven on, was on about an hour or so to burn off factory residues & smells etc, all looking good, nice and hot working fine...

Went to rotate knob to grill to burn that off, and as I moved it one click there was massive pop and a flashover from the consumer unit area, and the mcb (40A dedicated cooker circuit, nothing else on it except ceramic hob [which was off]) had operated, the RCD did not operate.

I rotated control knob back to O position and tried to reset the mcb, but again a huge pop & flashover right in my face, we are talking sparks flying out of the mcb all over the floor, major flashing..

In the end I could only reset the mcb by switching off the cooker switch on the wall, but as soon as I pushed it back down, POP and sparks flying everywhere again...

So I have swapped back for now and old one working fine again, and checked inside cons unit and everything is good and tight...

I took the back and top off the oven and had a good poke about, and all seems visibly ok, no loose wires or spades etc, no black marks anywhere..

Just wondering if anyone has any advice on how to start fault finding, be shame not to use it, its a brand new £300 oven...
I assume its likely either one of the elements or the control knob??
How do I test the elements?

Thanks..

 

[MJPD29]

Use your multimeter set to ohms to test the elements. Sounds like it could be an element, does it only happen when you turn the grill on? And all connections on the elements for the grill are ok?

 

[Wilko]

... Went to rotate knob to grill to burn that off, and as I moved it one click there was massive pop ... In the end I could only reset the mcb by switching off the cooker switch on the wall, but as soon as I pushed it back down, POP and sparks flying everywhere again ... So I have swapped back for now and old one working fine again ...

Hi - it does sound like a direct short circuit, I would not be trying it out again. FYI the "sparks flying out over the floor" is likely molten metal from that MCB and I'd replace it now, just saying. Probably only a few £. You will need some test gear to find out what's at fault within the cooker. The elements should be about 20 to 40 Ohms end to end and some meg Ohms to E, the outer metal covering of the element.

 

[dmxtothemax]

Most likely the griller element is faulty,
And probably shorting to ground.
New elements are readily available and not expensive.
check it with a ohms meter.
There should be high resistance to ground.
Anything less than a few meg ohms is faulty.

 

[SparkyChick]

Personally I'd be looking inside the cooker at the wiring loom/main switch.

If I understand the OP correctly, he turned the oven on and that was fine, turned the grill on and it went bang. Then he turned the grill off and was still not able to energise the cooker (he turned it off on the wall to reset the MCB and when he switched the isolator back on it went bang again).

 

[Misterbarlow]

Yes, it worked to start with on dual oven (no fan) setting for an hour or so, only when I operated the rotary selector it tripped, but I never even got to grill, only got one click,

clockwise it goes...

OFF (at 12 oclock)
LIGHT
DUAL OVEN (NO FAN)
TOP ONLY OVEN (NO FAN)
BOTTOM ONLY OVEN (NO FAN)
LOW GRILL (NO FAN) (6 oclock)
HIGH GRILL (NO FAN)
FAN HIGH GRILL
FAN DUAL OVEN
FAN LOW GRILL
OFF

I only switched from DUAL OVEN to TOP ONLY OVEN and it operated... then I could not re-energise it without tripping again, even in the O position...

 

[Deleted member 105166]

They got it brand new, don't know from where, cant find it on many websites, must have got it online??

Is there any visible corrosion on the internals?
If so, possibly substitute "online" for "on a beach"

 

[Misterbarlow]

Some more info...
I cannot find this model for sale online anywhere.

After speaking to the relative I got it from again today, they had some paperwork from the oven, it appears this model is not on general sale and only made to go in new build homes, and when they told me the name of who they bought it from, I put two and two together, I now suspect it's been half inched from a building site?

Hence why they were so happy to just cut their losses and buy another give it to me, and not attempt to take it back to a retailer etc..

So, that aside, I have just read on several sites that oven elements are hygroscopic and absorb moisture if sat a while, and it's common for some new ovens to trip the first few days of use until the moisture is dried out of the element.

If this has been sat in storage somewhere for maybe weeks, possibly in a portakabin on a site, or a half built house, then in my relatives garage for almost a month now unpacked with no plastic around it etc, could it be that an element has just absorbed moisture & needs drying out?

He told me in their house it was just tripping the mcb normally, not a violent spark fest like I had, so it's got worse during the time is been sat in the garage.

Thing is I am hesitant to power it up again now?

 

[Andy78]

This happened to my cooker once. All the missus did was wash it down with copious amounts of water. Turned out the selector unit behind the dial was fried after that.
Based on your description I would be surprised if there wasn't something black and crispy lurking about inside somewhere, and not a lost oven chip.

 

[ruston]

Repeated closing on the MCB is only going to make matters worse; as you are finding out.
If it is damp it would more likely trip the RCD not the MCB.
The only way to find the fault now is by dead testing using the methods previously described. I also agree there will be black crispy stuff inside now , probably the wiring harness as well as a faulty element.

 

[Misterbarlow]

Possibly found the culprit??
Checking all the elements with a megger, across the grill element blade to blade is 57, either blade to earth blade is zero.
Then noticed some blackening on one blade...

 

[DPG]

Was there something actually shorting the blade to ground then

 

[Misterbarlow]

Couldn't see anything, but at it's brand new everything is shiny and this is the only blacking I could see..

 

[Andy78]

The earth wire that lays across the blackened terminal when connected, that's not damaged and the source of the problem is it ?

 

[telectrix]

looks like a dead short L-E on that element.

 

[SparkyChick]

Looking at the two ends of that element with the blackening... the one which is black appears to be slightly longer than the other. Is there any blackening on the rear panel? I'm thinking manufacturing tolerances not good enough and it's shorted out to the case.

 

[DPG]

Whatever it is you need to be sure that you have found it - otherwise you risk it happening again.

 

[johnduffell]

Yes my money is on casing as well.

We bought a "seconds" oven cheap that was all dented on the external panels, goodness knows how looked like a fight with a fork lift.

I took all the flimsy back and bottom panels off and straightened as best I could and inspected before powering the thing up for the first time. Inside was very similar to yours apart from without the blackening in my case.

 

[Misterbarlow]

Good call JohnDuffell, just looked and didn't realise the back case is dented, looked on the inside and bingo!!



Bit of hammer work later and might wrap the blades in tape for extra, and I reckon it should be good to go...

 

[DPG]

Nice one!
I'd still consider replacing that MCB as well though. It's been closed on to a direct short several times now, and it sounds like it hasn't fared too well.