30mA RCD Tripping, New Induction Hob

[nitro23456]

Hi guys

New AEG induction hob fitted on 32 amp radial in 6mm cable, 45 amp dual connection unit to AEG hob (7.5 kw) and also electric oven (3.2kw).

All good for 3 weeks until today. My son flicks on bathroom light (4 x spots) and RCD trips. Single RCD protects all circuits on the CU. Plunged into darkness.

I turn off all MCB's and turn back on in turn after RCD on first. Last one to turn on is the radial. RCD trips again. I've checked all connections on this hob/cooker circuit and all is ok.

Again it trips when that circuit is turned back on. However, this time i turn this MCB on first and no trip. I get everything back on and then wife turns on bathroom lights and it all goes off again.

Everything is fine by itself, but a combination of everything now seems to trip RCD.

Advice please....

 

[JohnW2]

Any major spillages/floods in the vicinity of the oven/hob recently?

Kind Regards, John

 

[DetlefSchmitz]

So, definitely no circuits not protected by the RCD?

 

[JohnD]

you say there are a number of circuits passing through this RCD. It's quite possible that, excluding the hob, there is already a leakage of (say) 29mA. If this is the case, you need to identify the other sources of leakage. It is quite likely to be a watery appliance, such as a washing machine, kettle, fishtank, fountain, boiling water tap, outdoor socket or lamp exposed to rain, boiler or CH pump, or it could be PCs.

Try unplugging all appliances on the affected circuits connected to this RCD. Does the tripping stop?

Do both the upstairs lights and the downstairs lights pass through the same RCD?

 

[JohnW2]

Do both the upstairs lights and the downstairs lights pass through the same RCD?

... Single RCD protects all circuits on the CU. ....

Kind Regards, John

 

[DetlefSchmitz]

already a leakage of (say) 29mA.

...of course 14mA (+1) would do it...

 

[JohnW2]

...of course 14mA (+1) would do it...

In practice, probably true - but I don't think that an RCD is actually required to trip at half of IΔn, is it? ( I think that it is required not to trip below 0.5IΔn)

Kind Regards, John

 

[JohnD]

29mA used for comedic effect.

 

[EFLImpudence]

It must not trip at 15mA but must trip at 30mA - so anywhere above 15mA up to 30mA.

They're usually about 26mA.

 

[nitro23456]

I got as far as turning all sockets off, all MCB's off. Then RCD back on. All MCB's back on then started turning sockets back on one by one until wife decided to help matters by flicking bathroom lights on.

It seems everything is ok by itself but everything together is too much. I have aborted for the day. Everything is on other than the cooker circuit and everything is happy, but as I say I previously had this circuit back on as well but not with the hob/oven in use - this circuit seems responsible for a good chunk of the leakage.... is this normal for induction hobs? Was previously a ceramic hob.

No floods or spillages, I've had it all out and checked everything. And yes one RCD protecting everything.

Next on my suspicion list is the bathroom halogens as both my son and wife have now managed to trip - is it possible that a failing halogen (all 4 currently turn on) could be causing more of an earth leakage than say 3 weeks ago when everything was ok?

 

[JohnW2]

Next on my suspicion list is the bathroom halogens as both my son and wife have now managed to trip - is it possible that a failing halogen (all 4 currently turn on) could be causing more of an earth leakage than say 3 weeks ago when everything was ok?

Bulbs/lamps do not have an earth connection, and therefore can't really result in an earth leakage, per se, themselves.

However, if some appliance (commonly one in the kitchen or utility room) has developed a neutral-earth fault (often due to water), then, as has been said, switching on any load, anywhere (on the same RCD), can result in increased current though that fault, thereby potentially being the 'last straw' (which turns 29mA into 30mA, 26 mA into 27mA or whatever) that can result in the RCD tripping.

Kind Regards, John

 

[nitro23456]

Time for a professional i think.

What do you guys use to test this sort of thing?

 

[DetlefSchmitz]

In practice, probably true - but I don't think that an RCD is actually required to trip at half of IΔn, is it? ( I think that it is required not to trip below 0.5IΔn)

Kind Regards, John

As you probably knew, my point was that it is potentially a lot easier to trip an RCD than most people think. 15mA+ may be enough. Where the problem is 'random' tripping, this may be the reason. I won't post again, as it is not important to me to have the last word.

 

[JohnD]

it's possible to use a portable appliance tester on all your plug-in things. but not for hard-wired ones like your boiler (probably). I'd bet a pound to a penny it will be something watery, or a metal-sheathed heating element (as found in immersion heaters and oven elements). Outside lamps are watery. And I think more likely to be a combination of more than one thing. Unplug your washing machine tonight. Switching off is not as good as unplugging.

there is a faint chance it will be a damaged cable gnawed by rodents, but vanishingly improbable. It could be worsened by condensation in garage switches and sockets.

Reconfiguring your consumer unit may do the trick. A single RCD for all circuits is a recipe for disaster. Can we have some photos of it please.

 

[ban-all-sheds]