What might have caused RCD trip?

[pooksahib]

Hi. Every few years the element of my fan oven will 'blow'. The electric for the whole house cuts off and all I need do is flick the RCD switch back on and fit another element.

The current element is just a month old and yesterday dinner-time something odd happened: dinner was just about ready when the power went out and I was already blaming the new element. Unlike before, though, the RCD switch refused to be flicked. I had to turn the cooker off at it's socket before the RCD could be reset. Odd, I thought, still believing the element had failed.

This morning, I put the oven on just to be sure but it heated up no problem. So, if the element is sound and the cooker needed to be switched off in order to reset the RCD, can anyone suggest what caused last night's cut out? Thank you.

 

[AndyPRK]

its normal that if the element fails at one end, then you need to use the red switch to isolate it and switch the rcd back on.

I'm sure it will trip again in a few days !

 

[ericmark]

With a neutral to earth fault the current flow is dependent on the voltage difference between neutral and earth, in the DNO supply the two are connected together, so are normally the same, so the voltage with raise slightly dependent on load, so an earth to neutral fault with say a toaster with a bit of damp bread will not trip the RCD as the load is low say 600 watt, but as the load increases say switching on a kettle then the RCD trips as the neutral is rarely switched, so toaster left plugged in yet off causes the power to trip but it seems as if kettle is at fault.

So very likely there is a neutral to earth fault with some thing left plugged in. But the oven is a high load and has caused the voltage to raise on the neutral.

It is also possible that the element has absorbed water, and the oven being hot has pushed the water out again, the instrument used is an insulation tester that uses 500 volt, and rather than guess far better to test. I got a new un-calibrated one for £35 so not too expensive.

 

[pooksahib]

Interesting, thanks lads. In the past, I've never had to isolate the cooker before resetting the RCD but in all those past cases, the element was totally blown. In this case, where I had to isolate the cooker first, the element is still heating up so I'm guessing that when the element fails totally, it negates the need to isolate the cooker.

I've yet to cook another dinner with this element but if the same thing happens then it looks like, from what ericmark says, I'll maybe have to switch off a few other things around the kitchen...

 

[ericmark]

I'll maybe have to switch off a few other things around the kitchen...

Not switch as often a switch is on line only, unplug so neutral also disconnected.

 

[pooksahib]

Dooly noted...