Fan oven

[neiloneil]

After 2-3 years working perfectly, my Mums oven went pop the other day, accompanied by a plume of smoke and a smell of burnt electrics. I turned the power off, then turned the oven switch to off, then the power on, seemed ok, oven switch back on then got 3 or 4 pops in quick succession, so turned it all off and called an electrical repair shop.
The lady my mum spoke to said it sounded like a faulty fan, took the details of the cooker (New World 60edom) and sent a repair man around the following morning.
The repair man spent a while looking at the cooker, then informed us that the cooker is fine, but the house electrics are in a dangerous condition. He showed me on his mega meter that the neutral wire had continuity with earth. He said he couldn't do the tracing of the fault as he was only qualified to work on the appliance, but could recommend a good electrician to do it. That cost £44 call out.

It seemed strange to me that the circuit should suddenly develop a fault so I switched off power to the fuse box and tested the cooker socket. I found continuity between the neutral & earth wire so I disconnected the neutral output wire witch solved this reading and meant it was in the cooker cable junction box or the wires in between. I didn't find a short, but I re-made the connections and the whole thing seemed ok.
I double checked the readings , re-connected the cooker and turned the power on. Then I turned the oven switch on --- big bang, flash, and more smoke.

To me it seems like it must be a cooker fault. There is no earth short now unless its too high a resistance for my multimeter.

Can anyone suggest what may have happened, and what to do now?

 

[securespark]

How did he test for this fault and where? Was the oven disconnected at the time?

 

[Taylortwocities]

Indeed. Neutral is at, or very close to, earth potential so it would look like a short if he tested without disconnecting at the supply end.

If you are getting snap, crakle and pop from the cooker then it's the cooker.

If you disconnect the cooker from the supply (and insulate the ends) and turn on the supply. If you dont get crackles then its the cooker.

 

[neiloneil]

The cooker was just switched off at the wall switch.
He disconnected the neutral wire on the back of the cooker and put a probe on it, he touched the other probe on the cooker casing. His mega meter passed 500v, proving the short circuit.
My multimeter also showed up this short, but after tracing it to the cooker to wall connection box, the short disappeared.

 

[securespark]

What you say indicates an NE fault with the cooker.

That does not necessarily mean your fixed wiring is faulty or dangerous.

Did he test LE or LN as well?

 

[neiloneil]

I think he tested LE & LN, but not sure.
If, as you've both suggested possibly the cooker is at fault, then I need to be sure as it means I have been lied to and cheated out of money.
If I disconnect the cooker and test the terminals on the back should they all be insulated from each other? I will check these now.

 

[securespark]

It is difficult to get any reading of meaning with a multimeter. For insulation resistance tests, you really need an IR tester.

I don't know whether your oven includes any electronics in its circuitry.

I also don't know if it is the type that does not work unless the clock is reset.

It may be best to limit your tests between live conductors and earth. Omit the LN test.

You should find a minimum of 2 Megohm between LE and NE of the oven supply cable (assuming that cable is connected correctly).

OOI, why did he say that your installation was dangerous? Aside from the IR tests, did he do any others? Did he leave any paperwork?

 

[neiloneil]

they all showed open circuit (to my multimeter s precision).
I checked with the oven switch turned on and got continuity between L & N.

Update
Just tested with higher precision and got 4M ohms between L & N (all switches off)

 

[neiloneil]

Its difficult to read what he wrote. i'll scan it and put on here.
He didn't do any other checks to see if the mains supply was faulty as he was unqualified.

Untitled

• neiloneil
• 4 Jul 2009
• 1

 

[ColJack]

work caried out reads as "no fault found" and "checked with meger".

no idea what it says for fault reported..

as TTC said, disconnect the cooker entirely from the wall.. then switch the circuit and the switch back on.. if no flash bang then it's the cooker or the wire from cooker to the wall that's at fault..

I'd also put a stop on that cheque untill he's been round and tested it properly.. no way I'd pay 40 quid to be told it was house wiring without some proof..

or get a sparky out and if the house checks out ok, send him the bill as it was his insistance that the house was at fault that prompted you to get it checked...

 

[dextrous]

work caried out reads as "no fault found" and "checked with meger".

no idea what it says for fault reported..

disconnect the cooker entirely from the wall.. then switch the circuit and the switch back on.. if no flash bang then it's the cooker or the wire from cooker to the wall that's at fault..

I think you'll find it says - balance due £44.85, paid by cheque

 

[ColJack]

I think you'll find it says - balance due £44.85, paid by cheque

you being silly now?

it doesn't say that where it says "Reported fault:"

 

[dextrous]

I think you'll find it says - balance due £44.85, paid by cheque

you being silly now?

it doesn't say that where it says "Reported fault:"

Yep, just being silly. Anyway, Reported fault looks like "Earth fault" to me

 

[ColJack]

i thought that, but the E doesn't look much like an E to me, and the r looks different to the r in world, the r in cooker or the r in meger..

this is why I steadfastly refused to learn joined up writing in school....

the teacher called my parents in and told them while I was there, to which I replied " I can't read your remarks on my homework, or my parents writing, or even my own notes when I'm forced to write joined up, so I write in block capitols to make it easier to read"

 

[dextrous]

i thought that, but the E doesn't look much like an E to me, and the r looks different to the r in world, the r in cooker or the r in meger..

If you look at his "F"'s and add that looped flick at the bottom (the start of his pen stroke?), it does seem consistent with being an "E".

Think the "r" is a small "R" and his way of flowing into it from a capital "A".

But, enough of handwriting analysis (what's it called? calli.... (as in calligraphy, but that's not it) something?? ). Seems a bit mean to charge £40 and not actually resolve anything, especially if the op seems to have narrowed it down to being an earth fault on the cooker side of things and not the main circuit.