Electrical Shock from Oven?

[eveares]

Hi all, I have a new fan oven (Electrolux EOB8851AAX Steam Oven) what is a few months old and today i noticed i was getting very noticeable electric shocks of it when i was touching another earthed surface.

Now the oven is protected by a RCD and a suitable MCB (16A for the oven) like all circuits in our house (Had house rewire as part of a extension) and has is own 45A isolator with a plug, with a normal microwave fed from the isolators plug.

It is to note that while i am getting noticeable and rather painful shocks, the RCD has not tripped and am guessing so because the current imbalance is less than 30ma.

Now the other day i used the microwave and when i turned it on, a electric pop/bang occurred and stopped working/heating up the food - just assumed the microwave broke due to old age so replaced it.

Could the microwave of damaged my new oven causing what is normally a earthed surface to become live?

Finally I measured the voltage between the ovens surface and a earth in a plug socket with my multimeter and was getting a brief spike of around 20-120v of DC current before going back to 0v

(An yes I tried measuring AC current with multimeter, but got nothing!?)

Any ideas, help would be most appreciated.

Regards: Elliott V

 

[Spark123]

You shouldn't be getting 120vDC. I can't think of anything in an oven that would use that sort of voltage DC. Your RCD probably won't be able to detect DC, bog standard ones are an AC device.

With the oven off at the mains, can you measure the resistance of a metal part to your earth on the sockets and post back the result, it ought to be around zero ohms?

 

[eveares]

The voltage i was getting was normally 40-80v, but did on occasion go well over 100v!

It was like a spike of dc current was read then multimeter went back to 0v.

Also with the power off, there is no conductivity or total resistant between the metal part of the oven and the plugs earth - Because i have just found a screw missing what links the earth tab/connector to the metal case!!! :/

(My electrician wired it and had the L,N & E terminals fall inside the case!; i also think he found a screw as well if i remember rightly!)

Do you think i should replace the missing screw, would such a device normally create earth leakage, even while in standby/off?

Also my electrician has just also had his annual inspection on my propriety!

 

[bernardgreen]

It would appear that there is no effective earth connected to the cooker.

(My electrician wired it and had the L,N & E terminals fall inside the case!; i also think he found a screw as well if i remember rightly!)

More than likely part of the earthing circuit.

Do you think i should replace the missing screw, would such a device normally create earth leakage, even while in standby/off?

If it is a vital screw, such as the one that connects the earth cable to the cooker then YES

If there is no earth connection to the cooker there can be no earth leakage in the cooker until the cooker is earthed by someone touching it.

With only Live and Neutral connected the frame of the cooker will float some where between 0 and 230 volts due to capacitive coupling between wires and frame work. Very little current can flow through that coupling hence the voltage readings will seem strange as the loading of the meter will affect them.

If the micro wave blew up in a big way with a high earth fault current then there is a very remote chance it broke an already weak earth connection in the wiring leaving the cooker wthout an earth connection from the CU.

 

[crystal ball]

Had a similar problem at a customers last week, getting shocks from washing machine, tested socket circuit all ok, tested continuity to washer ok, but when it was plugged in via a 2 way adaptor no earth continuity, sprung connection in adaptor had become sloppy and not making contact

 

[FDJ]

It would appear that there is no effective earth connected to the cooker.

I would bet that there is a Delta or Y "suppressor" capacitor which, with the lack of an earth is causing the metalwork to float at 1/2 mains volts.

Frank

 

[eveares]

Thanks all, and sorry for the late reply!

Don't know a lot about capacitors; but when i put the screws in right after my last post the problem went away and everything was normal.

Were you suggesting that the electrical current was being induced to the case or that the case is directly connected to a capacitor.

 

[bernardgreen]

Two wires side by side act like a capacitor, a wire close to a piece of metal will act like a capscitor. The value is very small and refered to as stray capacitance. The amount of AC current that can flow through a stray capacitor is very small. Enough to give a tingle of a shock or make low energy lamps act strangely when the switch is OFF ( stray capacitor in the wires to the switch passes a small amount of energy to the lamp ).

Some equipment has real capacitors between Live and the frame, (which should be earthed) to act as filters to reduce voltage spikes and interference on the mains supply. These can pass enough current to give a more serious and harmful shock to some one touching the frame when the frame is not earthed.

 

[Spark123]

But it was DC, not AC.
Anyhow, glad to hear it has been fixed.

 

[FDJ]

It was like a spike of dc current was read then multimeter went back to 0v.

Meter should have been on AC V range NOT DC V.
OP is confusing Current and Voltage.