RCD tripping

[baps]

Hi folks,

We've had some sporadic tripping of the RCD recently. Probably needs a little background in case that helps.

• About a year ago, RCD trips and wont reset.
• Disconnect appliances one at a time until RCD resets; offending appliance seems to be old cooker.
• Remove the cooker, everything is fine so we replace the cooker. Just a cheap freestanding unit.

Now, perhaps once a month, the RCD will trip, usually when using the cooker. Strangely, it appears to be when we're turning off a ring or oven. RCD resets again just fine. This is a new phenomena though, didn't even know what the RCD was before the old cooker tripped it.

So, wondering if this is something that should be investigated? Did call an electrician we've used before, but he seemed to think "it's probably fine" and couldn't suggest a cause for this. Just not sure, so other opinions would be welcome.

Many thanks,

Baps.

 

[jj4091]

What type of rings do you have? The curly element type are just as prone to failing as oven elements which cause tripping of r.c.d., but it is slightly strange that it happens when you are switching off rather than on. Is it one particular element that causes the problem or any of them?

 

[baps]

Old cooker had those wires in a curly circle for the hob. New one has solid plates. Unfortunately, it's never happened when I'm using it, just the other half who says it's when she switches off a ring. I guess it's possible that's not what she's doing with it trips though (she panics a bit when it happens).

Baps.

 

[baps]

No other suggestions as to why this is could be happening or if it is likely to be unsafe? Would prefer not to pay for a callout to have a spark tell me there's nothing wrong/nothing they can do if I don't have to, so any thoughts appreciated.

Baps.

 

[securespark]

It's very tricky to diagnose an intermittent earth fault like this without specialist equipment. Even then, it can be a PIA.

 

[baps]

Would you suggest leave it then or do you think it may be unsafe?

Baps.

 

[John D v2.0]

It's possibly a fault elsewhere between neutral and earth. As a result when the neutral voltage increases due to the slight resistance, enough current goes via the cpc to trip the RCD.
If you get an electrician to do an insulation resistance test it might help with diagnosis

 

[baps]

Ok, thanks John!

 

[slippyr4]

I had something similar with the cooker where I used to live.

It'd occasionally trip the RCD then turning the oven off.

Turned out to be a faulty element- IR test was fine when cold but when I heated the oven, killed the power and tested quickly I got a much lower IR.

As to why it tripped when turning the oven off- I'm pretty sure that was down to the oven switch. It was a rotary multi contact switch that controlled several element functions by moving contacts with cams. The switch cut phase and neutral to the element, and I think it cut the neutral first, by a hairs breadth.

So when neutral disconnected, the faulty bit of the element was at 240V rather that some fraction thereof, so the fault current increased, from somewhat below 30mA to somewhat above.

Of course, that may or may not be what's happening here for the OP.