Domestic New cooker tripping RCD

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.

 

Are you saying you have a new fuseboard with a single up front RCD?

If so get the Muppet back who fitted it as it doesn't comply with the regs.

 

Deleted

 

So @maffoo why did you disagree?

I'm right btw

 

Yes, it's only a 10 way board as the room was limited so there's only room for 1 2P RCD.

 

Well it wasn't constructive at all - I came here for advice.

 

As I said in my original message, I purchased an earth leakage meter as I'm interested in finding out what is happening. If there are issues elsewhere in the house, I want to know.

 

My comment is where advice needs to start.

Who fitted this new fuseboard as it doesn't comply with the regs

 

An electrician fitted it. Any information on why it doesn't comply with the regs?

 

An earth leakage metre is a pretty pointless purchase unless you have the knowledge how to use it

Did the fuseboard installer give you any paperwork?

 

I do know how to use it. I didn't before I learned about it last week but it's not rocket science.

Yes, I have paperwork. Again, what regulations does it not comply with?

If you believe the RCD tripping issue lies with the consumer unit installation quality then that's fine. Otherwise, I'm being led down the wrong path and still have a potentially faulty hob/cooker. When you guys have tested hobs/cookers/appliances etc. previously, what would expect the earth leakage to be? Is an item considered faulty if it's above a certain mA?

 

As Murdoch says, your whole house should not be on one single 30mA RCD - you loose power to everything in the event of a fault (or, as may be the case here, the cumulative leakage gets above the trip threshold of your RCD).

You really need to get the electrician who fitted it to install something more suitable. RCBOs for each circuit is the best setup - you'd still get 8 usable ways as you have now. At the same time they could perform some tests on the installation (these may have and should have been done before the board change) and the cooker to make sure there aren't any underlying issues that are contributing to this problem.

 

If there was limited space RCBOs would have been a good option.

The first tool I grab when looking for this sort of fault is an insulation resistance tester. For cooking appliances the maximum permitted earth leakage current is 0.75mA per KW up to a maximum of 5mA

 

Inspection and testing needs to be carried out before you start swapping things over.

As you have one RCD protecting the whole installation you may well be getting a cumulative effect combined from other circuits causing the RCD to trip.

Not having enough space is no excuse when there's other options such as RCBOs available.

As for non-compliance of regulations, 314 Division of installation has a couple of relevant lines.

 

Thanks, that's what I was looking for - an actual suggestion

So, get rid of the 100A RCD for 100A main switch and replace the MCB's with RCBO's?