Halogen Hob Problems

[Mattman]

Hi all!

so I a chippy I work with installed a little kitchen, all appliances supplied from howdens - this particular brand is Lamona.

existing 32A ring was extended to pick up a few items (mini extractor, built in microwave, the hob and a countertop twin socket. Circuit tested out fine - a good R1R2 and a clear >1000M on IR. also tested the RCD for a solid result and ramp tested it to a comfortable 28mA operating current. I have not used an earth leakage monitor as I don’t have one.

however, the RCBO is intermittently tripping... I’ve isolated it down to the hob. I’ve had the hob running at full load and it’s fine, but every now and then when it’s not on (but energised) it drops the breaker off. Can’t get in touch with Lamona (a part of howdens that offer next to no technical support) so I thought I’d offer it out to anyone who may have had similar problems before and may have found a solution before I airmail the hob out of the window.


Thanks!

 

[DPG]

Cumulative leakage on the circuits connected to the RCD?

 

[stevethesparks]

I wouldn't expect to see a ceramic hob run from a final ring circuit. What its ratings?

 

[Mattman]

3kw

 

[Mattman]

Cumulative leakage on the circuits connected to the RCD?

Hmm, I was thinking that a while back but I was a

I wouldn't expect to see a ceramic hob run from a final ring circuit. What its ratings?

3kw

 

[stevethesparks]

A 3KW hob should not be plugged in to a final ring circuit and should have its own supply.

 

[telectrix]

3kw

should be on it's own circuit. RCBO would be ideal if you have the option.

 

[pc1966]

Is that ring only for the kitchen, or the whole floor?

I would go with @DPG thought and see if you can borrow a clamp meter able to measure the leakage current when running. To buy the cheapest seems to be the "HandyMAN TEK775". Remember you have to clamp both L &N but not E at the same time, so it needs safe access to the cables at some junction or termination point.

As others have pointed out, 3kW is a bit high for a "fixed load" even though it is 13A and within a socket's rating.

 

[Mattman]

Is that ring only for the kitchen, or the whole floor?

I would go with @DPG thought and see if you can borrow a clamp meter able to measure the leakage current when running. To buy the cheapest seems to be the "HandyMAN TEK775". Remember you have to clamp both L &N but not E at the same time, so it needs safe access to the cables at some junction or termination point.

As others have pointed out, 3kW is a bit high for a "fixed load" even though it is 13A and within a socket's rating.

God, this site really bombards you with ads, I’ve been posting half written responses all over because I’ve lost myself! ?

Yeah, looks like a leakage tester is best way forward - saves me going back anymore.

Just a quick few things I probably wasn’t clear on...

The ring is dedicated to that small kitchenette only - items attached are the hob, built in microwave, extractor hood and a double socket. The hob itself isn’t on a plug, it’s on the ring but I’ve put that on its own little 16a inline. Yeah I agree a dedicated circuit is usually called for, but the damage to the fabric of the building running that supply in was a bit daunting for the customer, coupled with the load requirements for the hob, i thought it was a bit unnecessary. If I’ve missed a reg somewhere then I’ll hold my hands up and put it right.

Thanks to you and DPG for the shout.

 

[pc1966]

If it is just the kitchen then it is a bit odd to be tripping the RCD as there is not a lot on that circuit.

Some electronics has high leakage due to the noise filters so an induction hob is possibly a reason though they ought to only be a couple of mA. But until you can check what is actually happening with stuff on it is hard to tell. Ideally they would give you the information up-front, but a measurement is going to tell you a lot more about what is going on!

 

[Mattman]

If it is just the kitchen then it is a bit odd to be tripping the RCD as there is not a lot on that circuit.

Some electronics has high leakage due to the noise filters so an induction hob is possibly a reason though they ought to only be a couple of mA. But until you can check what is actually happening with stuff on it is hard to tell. Ideally they would give you the information up-front, but a measurement is going to tell you a lot more about what is going on!

Yeah I’ve been reading up on some of the kit dumping small currents to earth for various reasons. The trouble is, the issue is happening so irregularly - I’ve IR tested it with all loads connected to see if there’s evidence of a short somewhere but it’s clear on all accounts. The customer is saying that he’ll get into work in the morning and find it’s tripped out, switch on and it’ll be fine for a few hours before tripping out again. The units are energised but not in use when it trips and when I do put them into use they run fine. If I test it and the earth leakage is near enough to the limit anyway then that should paint a solid picture. Something is going on in the night hours and kicking it out. I’ll look up your link for a metre and pick one up.

 

[pc1966]

If the 'normal' leakage on the whole ring circuit is significantly below the 15mA lower trip limit for the usual RCD and you have ruled out N-E faults by the IR testing then it would not have a good reason to go. But there might be something else happening that makes it trip-happy.

One guy a few months ago was seeing his RCD trip during voltage disturbances when the weather was bad and (presumably) cables coming down, etc. So it might be something outside of the new appliance but the extra capacitance has pushed it close enough to trip on that sort of event.

But get a measurement first and see if it is currently sailing close to the wind, or if it looks to be a non-obvious fault to chase.