Oven not tripping RCD

[shabz]

This oven that has meggered in at only 0.35mohms (faulty grill element), it is on a RCD protected circuit however it does not trip the RCD. I have tried it on one of those plug in 30ma RCD and it does not trip that either. Shouldn’t the rcd trip with such a low resistance reading?

[leavemetogetonwithit]

Re: Oven not tripping RCD

I did once ask on here how low an appliance has to go to activate the trip and I calculated 8000 ohms (30ma / 240v) using Ohms law. No one answered to confirm, so I guess no-one really knows.
1 megohm is the safety limit. It has to be well above what will actually cause a trip situation to allow plenty of margin. And still not all dwellings have trips so you’d need 30+ amps of fault current and some, to flow to protect you in those situations! So that’s why the earth’s so important.
Ask Martin to give you lots more info. 😀
Mike.

[Seamy]

Re: Oven not tripping RCD

Depends on the installation & how good it is in particular the earthing, if its a neutral to earth problem sometimes it won’t trip. Put a clamp meter in the earth connection to the appliance in question & moniter the leakage current, anything above 28mA should trip a 30mA RCD.

[Brains]

Re: Oven not tripping RCD

You will find that most RCDs will start tripping at about 22mA. This is due to cable capacitance.

The 30mA trip rating for RCDs was set based on shock current survival rates 😈 (can’t remember the EN standard for this).

Keep in mind that most modern RCDs operate based on differential current measurement. i.e difference between line and neutral currents.

350kohms represents about 0.7mA of leakage.

Keep in mind that when you measure the insulation resistance of an element it is cold. When hot, the element insulation resistance could be driven a lot lower.

HTH

Regards

[Pigpen4]

Re: Oven not tripping RCD

Have you checked for correct wiring?

I went to a cooker the other month that was ‘playing up’, to find that one of the rings was below 1 meg and it hadn’t tripped the RCD.

The oven wasn’t working properly, was the reported fault.

Her ex- had installed it and connected the brown to the blue and the black to the red wires – see http://www.flickr.com/photos/pigpen4/5409598165/

I think she was very lucky!

[neon_3SP_glow]

Re: Oven not tripping RCD

Pigpen4 wrote:Have you checked for correct wiring?

I went to a cooker the other month that was ‘playing up’, to find that one of the rings was below 1 meg and it hadn’t tripped the RCD.

The oven wasn’t working properly, was the reported fault.

Her ex- had installed it and connected the brown to the blue and the black to the red wires – see http://www.flickr.com/photos/pigpen4/5409598165/

I think she was very lucky!

I had this exact fault few weeks ago. It suprised me that the machine worked at all, but almost everything was ok apart from the fan oven cutting out after a few seconds. Madness

[shabz]

Re: Oven not tripping RCD

Thanks all for shedding some light on this 😉

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