Live discharge to earth on lighting

[soamesi]

Hi All

It's been a while but I wonder if someone may be able to assist and save me some time.

I have been asked to go and have a look at a lighting circuit in a 60s house tomorrow because there is discharge to earth which the customer has noticed via the wall plate screws when tightening a switch. Further inspection by him has noticed that it is almost like a capacitor discharge in that it takes a while to charge up but when using an electrical testing screwdriver (!!) the bulb lights and fades straight away.

To save me a bit of time, does anyone have any ideas what maybe causing this?

The customer tells me that it is an old bakerlite fuse board where the rewirable fuses have been replaced with pop out trips so I suspect that there is no lighting earth all the way around the circuit even though the switch drops are all earthed.

Any assistance very gratefully received as I am only popping out as a favour - I am supposed to be on another job.

 

[Marvo]

I'm not about to save you any time, it's hopefully going to double the work for you in fact.

If you've got a CPC (earth wire) that's becoming live then you've actually got 2 faults that you need to find so take your megger tester and your loop impedance tester with you.

 

[Deleted member 9648]

Best advice would be to get an electrician to attend the site.

 

[soamesi]

Best advice would be to get an electrician to attend the site.

Ho, ho, ho. Merry Christmas!

I shall be going to site as a domestic electrician/installer. However, I am supposed to be elsewhere and trying to save time. This site is supposed to provide assistance rather than belittle the less experienced. But thanks for your input!

 

[soamesi]

Thanks Marvo. I will be taking the testing kit, just wanted to see if anyone else had come across this style of earth fault before (i.e. seems to "fizzle out" as soon as something such as a test light on the screwdriver uses the charged energy).

Wasn't really looking to double the time as too much on already and trying to do as more of a favor for a relative of the disabled inhabitant.

 

[davesparks]

What exactly is the fault here? from what i've read it sounds like someone is poking a neon screwdriver in places where it doesn't belong (the only place they belong is in the bin) and watching a bit of static electricity discharge to earth through it.

 

[Deleted member 9648]

Ho, ho, ho. Merry Christmas!

I shall be going to site as a domestic electrician/installer. However, I am supposed to be elsewhere and trying to save time. This site is supposed to provide assistance rather than belittle the less experienced. But thanks for your input!

I feel you have just proved everything that is wrong with the dumbing down of qualified electricians.Nothing personal,but here you are....on a forum...asking what the likely cause of a very simple fault situation is so you can charge a client for your expertise. Dont get me wrong,it's not your fault,it's the system.Apologies if it comes across as belittling you,that wasnt my intention.

 

[soamesi]

Thanks Wirepuller. I am qualified and have only had a chat on the phone with this guy who is a friend of mine and hence trying to do him a favour. Normally, the customer would have had to wait but because of the friendship I said I would pop in tomorrow while I should be on another job. Hence trying to save a bit of time.

 

[Deleted member 9648]

Thanks Wirepuller. I am qualified and have only had a chat on the phone with this guy who is a friend of mine and hence trying to do him a favour. Normally, the customer would have had to wait but because of the friendship I said I would pop in tomorrow while I should be on another job. Hence trying to save a bit of time.

Ignore me....it's time of the month again.

 

[soamesi]

Dave, I suspect it might be as simple as static or maybe a proximity voltage carrying across close situated cables. I'll put a meter across it tomorrow and see what is what.

 

[davesparks]

Dave, I suspect it might be as simple as static or maybe a proximity voltage carrying across close situated cables. I'll put a meter across it tomorrow and see what is what.

A proximity voltage? What on earth is one of them?
And what are you going to put your meter across? For that matter what meter are you going to put across it?

 

[soamesi]

Not the right words and I can't think for the life of me what the right phrase is. I have read in the past about a small voltage "jumping" across cables where routed together. It may be a load of rubbish of course and I can't recall where I read it - it was a long time ago.

Either way, I will use a wander lead between the distributors incoming earth and the alleged live switch back box and see if there is a voltage reading or indeed any continuity (which I doubt). I have a Megger MFT.

 

[davesparks]

Either way, I will use a wander lead between the distributors incoming earth and the alleged live switch back box and see if there is a voltage reading or indeed any continuity (which I doubt). I have a Megger MFT.

Why do you doubt that there will be any continuity, you said earlier that there are earths at the switches? plus of course the fact that the neon is glowing then fading suggests that something is flowing to earth through it.

 

[trev]

Why is the customer tightening switches?
Please tell him not to use a neon.
Come to think of it, please tell him to stop buggering about with things he knows nothing about.

 

[Marvo]

Rather just test the circuit methodically as described in GN3 I believe. Voltage readings don't mean a lot if you're using a digital tester or MFT.

 

[BES]

Not the right words and I can't think for the life of me what the right phrase is. I have read in the past about a small voltage "jumping" across cables where routed together. It may be a load of rubbish of course and I can't recall where I read it - it was a long time ago.

Either way, I will use a wander lead between the distributors incoming earth and the alleged live switch back box and see if there is a voltage reading or indeed any continuity (which I doubt). I have a Megger MFT.

What did they teach you about the science and priciples of electricity on your domestic installers course. Not a criticism just wondering ?

 

[soamesi]

Just a suspicion from the description of the CCU. I suspect that any earths on switch boxes in a 60s house with a bakerlite board might just be because of rewired/moved switches. Apparently, after a "glowing then fade" situation, it takes a while for the fault to recharge itself - which is why your suspicion of static may well be spot on.

 

[soamesi]

Thanks. He has replaced some dimmers with wide switch plates as the disabled occupant could no longer grip the dimmer control to turn the light on and off. He does know a fair amount about electrics and replacing switches is perfectly permissible (albeit, perhaps not advisable).

 

[Marvo]

I'm not a big fan of the static theory at least until the circuit in question has been inspected and tested.

 

[soamesi]

Yes. In the absence of anything obvious, I'll do exactly that. Thankfully it is a bungalow so cabling should be relatively easy to get to (famous last words) if I need to replace anything.
Thanks