Turn off hob and both MCB and RCD trip.

[satori]

Parents in law are experiencing and intermittent fault. Occasionally, when one of the rings on the hob (I think the hob is of the induction type) is turned off, both the hob MCB and the associated RCD trip. I can't envisage a fault that would trip both.

The property is a bungalow that had an extension added about a decade ago (the hob dates from that time). At that time the CU was replaced, for diversity the circuits were divided between two RCDs. The hob and oven (an MCB each) and all the sockets[1] are on one RCD; the other RCD has all the lighting and the immersion heater.

I'm intending to borrow a tester from work and pay a visit, but I'd like to go with a better idea of what I should be looking for. My intention, before suggestions from the wise here, are as follows:

* Safe isolation!
* Take a look inside the CU and check all connections.
* Check connections in the isolator local to the hob.
* Check continuity on R1, R2, and Rn of all circuits associated with that RCD.
* IR test the circuits associated with that RCD (with the hob circuit I intend to do so with the isolator off, then on - are there likely any sensitive electronics in an induction hob that won't like a 500V IR test?).

I'm a bit concerned about having to pull the kitchen apart to get at wiring for the hob if I find there is a fault down-stream of the isolator.

How does the above sound to you? I'm going to have a chat with the guys at work on Monday, but we're mainly industrial, and I'd like a broader experience than my colleagues can offer!

Thank you for any suggestions on a better way to proceed.

[1] I don't yet know if the sockets are on RFC or radial. It being an old bungalow with an extension, I'm worried the builder may have the extension as a spur, but this is relatively ancient history, no one would remember. I can only hope he did the right thing - I don't know if the in-laws even remember who did the work.

 

[Octopus]

You are over thinking this ..................... need more "facts"

RFC or radial - is this even relevent?

 

[satori]

You are over thinking this ..................... need more "facts"

RFC or radial - is this even relevent?

Probably not. Just trying to give as much info as I can (obviously relevant info is worth much more than the irrelevant kind). What other facts would be relevant? I quite possibly don't have them to hand and in-laws are getting old and ...ummm... how do I put this politely? .... not agile of mind - meaning they don't understand and therefore give irrelevant answers to pertinent questions!

 

[123]

Is it the same ring each time or do all the rings do this?

It's most like to be a fault in the hob imo

 

[Pete999]

Parents in law are experiencing and intermittent fault. Occasionally, when one of the rings on the hob (I think the hob is of the induction type) is turned off, both the hob MCB and the associated RCD trip. I can't envisage a fault that would trip both.

The property is a bungalow that had an extension added about a decade ago (the hob dates from that time). At that time the CU was replaced, for diversity the circuits were divided between two RCDs. The hob and oven (an MCB each) and all the sockets[1] are on one RCD; the other RCD has all the lighting and the immersion heater.

I'm intending to borrow a tester from work and pay a visit, but I'd like to go with a better idea of what I should be looking for. My intention, before suggestions from the wise here, are as follows:

* Safe isolation!
* Take a look inside the CU and check all connections.
* Check connections in the isolator local to the hob.
* Check continuity on R1, R2, and Rn of all circuits associated with that RCD.
* IR test the circuits associated with that RCD (with the hob circuit I intend to do so with the isolator off, then on - are there likely any sensitive electronics in an induction hob that won't like a 500V IR test?).

I'm a bit concerned about having to pull the kitchen apart to get at wiring for the hob if I find there is a fault down-stream of the isolator.

How does the above sound to you? I'm going to have a chat with the guys at work on Monday, but we're mainly industrial, and I'd like a broader experience than my colleagues can offer!

Thank you for any suggestions on a better way to proceed.

[1] I don't yet know if the sockets are on RFC or radial. It being an old bungalow with an extension, I'm worried the builder may have the extension as a spur, but this is relatively ancient history, no one would remember. I can only hope he did the right thing - I don't know if the in-laws even remember who did the work.

You mean r1 r2 and rn which are the end to end readings on a RFC get the simple things right the rest should fall into place, the builder could have installed the sockets as a Radial, which is different from a spur, as your colleagues at your work should be aware of. If your colleagues are Electricians they must be aware of the differences.

 

[Gavin John Hyde]

My instinct would be to have a look at the hob. Have experienced something similar with a cooker, it would intermittently trip the breaker and always trip rcd when the oven or grill were turned on, Turned out the heating elements/system inside were on the way out and somehow causing a fault. Never established exact fault but it drove me mad as all the electrics tested out okay in the house.
I got the customer to contact john lewis who they bought it from. the engineer confirmed the heaters inside were dud and they replaced the whole cooker as it was cost and time effective way to deal with issue, afterwards no tripping.

Maybe put a earth clamp on the hobs flex to see if there is anything amiss?

 

[Octopus]

Probably not. Just trying to give as much info as I can (obviously relevant info is worth much more than the irrelevant kind). What other facts would be relevant? I quite possibly don't have them to hand and in-laws are getting old and ...ummm... how do I put this politely? .... not agile of mind - meaning they don't understand and therefore give irrelevant answers to pertinent questions!

The ones you conclude are relevent when you've been onsite!

 

[UKMeterman]

Ah, the clue is Induction hob. Often these have a lot of filter capacitiance L to E and N to E that can cause transient trips. Check the installation with a 500V megger to see if there are any other issues, and you might want to move the hob to it's own RCBO

 

[Dave OCD]

And although unrelated to the current issue having both lighting circuits via the one RCD is poor design, especially with elderly customers.

 

[123]

And although unrelated to the current issue having both lighting circuits via the one RCD is poor design, especially with elderly customers.

If new consumer unit has been fitted, chances are it's there because of a borrowed neutral. So worse than a bad design, it's dangerous

 

[telectrix]

And although unrelated to the current issue having both lighting circuits via the one RCD is poor design, especially with elderly customers.

and the house should have 2 separate 100A supplies, so if 1 goes down, the other will still give them power and lights.

 

[Dave OCD]

Are you on the beer Tel ?

 

[The Ghost]

When they are switched off are they off load? I am thinking something wrong with the switches. If as you say the observers/reporters are not the sharpest knife in the draw, it seems you may have to verify what has been stated.

 

[Wilko]

By all means make checks, but I'm thinking the induction hob is not working correctly. It should not trip the MCB instantly ...

 

[elsparko]

disconnect the hob if problem is solved buy a new one, occams razor