Non contact tester showing cooker live. Random shocks in kitchen.

[Harry Bloomfield]

What you say makes perfect sense, something making the case live, but why isn’t this being discharged to earth, is the other quandary. Could the mcb be faulty?

Maybe now is the time to just get a new rcb board and get the whole house earths checked.

Your more immediate problem is to identify as a matter of absolute priority, what is actually live. You can do that, as suggested above, by connecting meter in turn between each appliances metalwork and a known and reliable ground. If necessary, extend the lead to ground, with an extra length of wire.

Once you have identified the live item, then turn it off via the MCB if the oven, or unplug the toaster.

If the toaster, then you need to ensure the earth pin at the socket is not live and if it is you would need to isolate the kitchen ring.

 

[dabaldie]

Thank you. Just isolated the cooker circuit and pulled the front off the socket/double pole switch and hey Presto… earth wire not connected properly in the switch! It just fell out if it was even in there properly. May have just been touching the common earth “bar”

So that explains it all. Pan boiled over which has caused something inside to cause the case to go live. This wouldn’t normally be dangerous I guess because the earth would cause the mcb to fail. Maybe it failed the first few time because of the “weak earth connection “
But as there was no proper earth the case went live and gave a danger.

Thanks for all your help!!
Cooker is just out of warranty so probably not worth trying to fix. Although I may ask a local guy.

 

[JohnW2]

Thank you. Just isolated the cooker circuit and pulled the front off the socket/double pole switch and hey Presto… earth wire not connected properly in the switch! It just fell out if it was even in there properly.

Fair enough.

So that explains it all. Pan boiled over which has caused something inside to cause the case to go live. This wouldn’t normally be dangerous I guess because the earth would cause the mcb to fail.

Probably not. If it (and the shocks) were a consequence of water ingress , even with the case properly earthed, that would not commonly cause an MCB to trip - but it would trip an RCD (which is why we have RCDs).

However, how recent was this "boiling over". Electrical leakages due to that cause usually sort themselves quickly (when thiungs dry out) - particularly in the current weather!

Cooker is just out of warranty so probably not worth trying to fix. Although I may ask a local guy.

As above, the problem might sort itself out.

Kind Regards, John

 

[sparkwright]

You need to assume the worst, and assume you have an earth fault or faults in the house.

It must be looked at immediately by a competent electrician.

 

[ericmark]

PD stands for potential diffrence, clearly you have found one fault, but to get a shock what you touch nees to be a diffrent voltage to you.

Birds can land on power cables, so when we get a shock we need two items with a diffrent voltage, so we talk about bonding rather than earthing.

As time has gone by, it has become harder and harder to ensure all items are bonded together, plastic pipe joints and pipes, and even plastic sealing tape used on plumbing joints.

In 2008 the regulations recognised this, and it was permitted not to bond in bathrooms as long as you have 30 mA RCD protection, as it has become harder and harder to ensure all exposed metal work is at the same voltage.

I would expect you have a whole list of faults, when I tried to add RCD protection to my parents house, I had to abort until house was rewired.

But you don't today really have an option, it needs testing, correcting, and RCD protection added.

 

[winston1]

Thanks for all your help!!
Cooker is just out of warranty so probably not worth trying to fix. Although I may ask a local guy.

I hate this modern throw away attitude. You have already binned a perfectly good kettle on an (incorrect) hunch, and now you want to throw away a cooker just out of warranty (but probably not beyond the Consumer Rights Act).
The fault was no earth on the cooker causing slight shocks. Put the earth back and see what happens.

By the way non contact voltage testers are unreliable and are the things that should actually be binned.

 

[JohnW2]

I hate this modern throw away attitude.

So do I, but ...

The fault was no earth on the cooker causing slight shocks. Put the earth back and see what happens.

A bit more than just that. He apparently measured 235V between the cooker casing and an earth - so, if that is a true measurement (unlikely to be 'stray pickup, at that level), then what will 'happen' could well be a 'bang' - hopefully just as a result of the MCB operating, but maybe more. I would certainly not advise him to re-energise the cooker 'after putting the earth back', given that history.

The situation clearly needs to be investigated and, in modern parlance, 'sorted', as a matter of some urgency.

 

[dabaldie]

I only used the pen to see if there was anything that was going live to give my wife the shocks such as the washing machine that I couldn’t get a good earth off without scratching paint. Useful to scan for voltages quickly I guess.

The kettle didn’t actually go in the bin it went to work where it was pat tested and and passed and is now being used in the office!

As for reenergising the cooker, I reconnected the earth, and did power it back up. But I knew there must be more to this other how was the case getting voltage in the first place.
Case showed 0v with the earth reconnected.
I then listened carefully as I could hear a faint crackle buzz from the cooker isolator even with the cooker not actually on (but isolator in the on position).

At this point I’m not going further and risking anything. There’s clearly an issue with either a short in the cooker or the isolator. I wasn’t going to wait for a Big Bang/fire/mcb or worse.
MCB was switched off immediately.
The isolator is old so has gone in the bin.

I’ll get a professional (he/she) in this week to get the isolator changed (wiring is buried in the wall (not in metal conduit either!) so I guess he’ll have to surface mount new cabling unless I get RCD CU installed )

When he fits the new isolator he can then connect the cooker and check for a fault with that I guess? It’s a hotpoint and I tried taking an old one apart once to see how it was made and it was all pretty much sealed/glued together.

Warranty or consumer rights wouldn’t help me as it was almost certainly caused by a pan boiling over, that’s when this all started with the first MCB trip. Maybe it could be argued that the cooker should be protected against that as that is “normal use” but I’d also say user error.

Either way, I’ve learnt something this evening. The cooker is isolated and the isolator is in the bin so no one is getting hurt today.

I’ll update at some point if any fault is found with cooker.

 

[winston1]

I

The kettle didn’t actually go in the bin it went to work where it was pat tested and and passed and is now being used in the office!

OK.

As for reenergising the cooker, I reconnected the earth, and did power it back up. But I knew there must be more to this other how was the case getting voltage in the first place.

Already explained. Leakage through capacitors in the absence of an earth.

Case showed 0v with the earth reconnected.
I then listened carefully as I could hear a faint crackle buzz from the cooker isolator even with the cooker not actually on (but isolator in the on position).

Hm.

At this point I’m not going further and risking anything. There’s clearly an issue with either a short in the cooker or the isolator.

Short in the cooker would immediately trip the MCB.

I wasn’t going to wait for a Big Bang/fire/mcb or worse.
MCB was switched off immediately.
The isolator is old so has gone in the bin.

Being old is not a good reason to bin it.

I’ll get a professional (he/she) in this week to get the isolator changed (wiring is buried in the wall (not in metal conduit either!) so I guess he’ll have to surface mount new cabling unless I get RCD CU installed )

When he fits the new isolator he can then connect the cooker and check for a fault with that I guess?

Let us know what he finds.

It’s a hotpoint and I tried taking an old one apart once to see how it was made and it was all pretty much sealed/glued together.

Warranty or consumer rights wouldn’t help me as it was almost certainly caused by a pan boiling over, that’s when this all started with the first MCB trip. Maybe it could be argued that the cooker should be protected against that as that is “normal use” but I’d also say user error.

Either way, I’ve learnt something this evening. The cooker is isolated and the isolator is in the bin so no one is getting hurt today.

I’ll update at some point if any fault is found with cooker.

 

[JohnD]

Could the mcb be faulty?

no reason to suppose so

the current required to kill you is far, far less than it would take to trip the MCB

 

[Harry Bloomfield]

no reason to suppose so

the current required to kill you is far, far less than it would take to trip the MCB

Of the order of 3,000 times less current needed to kill you, dependent on the MCB rating. MCB's are designed to protect circuit components, not people.