New cooker tripping RCD

[maffoo]

Firstly, I am not an electrician so please go easy on me and if I have omitted anything please ask.

We've had a new cooker and induction hob installed from Ikea. Here's some information on the setup :-

• New consumer unit, 100A 30mA RCD feeds 8 MCB's
• First MCB in line from the RCD is a 40A MCB for the cooker
• New cable from the above MCB to cooker switch (10mm)
• New cable from cooker isolator switch to cooker terminals behind cooker (10mm)
• Induction hob wired in to cooker terminals (2.5mm)
• 13A fused spur wired in to cooker terminals which feeds the cooker (hard wired cable from cooker)

The RCD is intermittently tripping and it "appears" to be the cooker/hob causing this. Here is some information about the various situations after some troubleshooting :-

• Cooker and hob work fine, appear to have no issues
• The RCD has never tripped whilst the cooker or hob have been in use, even at the same time
• The RCD has never tripped whilst the cooker switch has been turned off
• The RCD has tripped only once when turning on, but mostly when turning off
• The RCD trips hours after the cooker/hob has stopped being used, but isolator switch remains turned on
• On one occasion I couldn't get the isolator switch to turn on without the RCD tripping. After switching off the fused spur to the cooker (leaving only the hob) the power could be turned on. As soon as the fused spur to the cooker was turned on, the RCD tripped again

So after troubleshooting the above, I assumed it was the cooker causing the issue so phoned Ikea and they sent a replacement. However, this is physically damaged so also needs to be returned. In the meantime I have read up on earth leakage and got myself an earth leakage meter as there are a lot of recommendations that maybe the leakage is nearing 30mA throughout the house and it may be the hob/cooker are causing this to go over the threshold.

I've not had time to test everything throughout the house yet but I've measured the hob earth leakage and it's 5mA. Considering the whole house is limited to 30mA, this seems a bit high to me. What is the "normal" leakage for an appliance like this? I will test the cooker shortly too and I suspect that this could be "high" as since the cooker has not been connected at all, the RCD hasn't tripped with only the hob connected.

Any comments appreciated.

 

[Toneyz]

Surely instead of all or nothing approach, why not a mix of MCB's and RCBO's as appropriate? But the sum total of leakage is a concern

1. The OP has already got the consumer unit fitted and would be a waste of money spent.
2. I don't think the OP has the room for a split consumer unit.

 

[maffoo]

Wow, catching up on all that was interesting

Quick update: All MCB's have now been replaced with RCBO's and I've had no issues since. Granted, I've had the cooker replaced since then but it's very unlikely that was causing the issue.

In response to the "why buy an earth leakage tester?" question. I'm just a very technical person with an interest in almost everything. I wanted to narrow down the problem myself. I'm not saying I'm qualified to do what most people do on these forums, but I've learned some things and that's better than when I originally posted the question. Totally unrelated, there's a cheap earth leakage tester on eBay if anyone is interested

 

[DPG]

Thanks for the update Maffoo.

 

[telectrix]

Wow, catching up on all that was interesting

Quick update: All MCB's have now been replaced with RCBO's and I've had no issues since. Granted, I've had the cooker replaced since then but it's very unlikely that was causing the issue.

In response to the "why buy an earth leakage tester?" question. I'm just a very technical person with an interest in almost everything. I wanted to narrow down the problem myself. I'm not saying I'm qualified to do what most people do on these forums, but I've learned some things and that's better than when I originally posted the question. Totally unrelated, there's a cheap earth leakage tester on eBay if anyone is interested

you got a link to that el tester?

 

[DPG]

Search earth leakage tester and scroll down until you see the red second hand one that is currently around 32 quid. And then click the agree icon

 

[telectrix]

similar to the cheapo i got.poor resolution and prone to giving erratic readings. jaws won't clamp 2 x 25mm tails, but a useful tool in conjunction with MFT , common sense, and scribes on a beermat.

 

[oracle]

I have a Fluke 360 earth leakage current clamp and it is very accurate right down to I micro amp, which subtends to 240 Mohms insulation resistance.