230v AC Electrical Query: Why do I get voltage on an open wire?

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Razer0

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Hello friends

A query that's baffling me: I am a qualified electrician but you don't learn this stuff in school, unless you use wisdom to figure it out. This is where you come in.

In a situation today, I come across a set of joined wires that needed to be encased in an enclosure, in this case a PVC 3-way round box with glands, lid, screws, and sprague piping. In SANS 10142, I believe (I am not accredited with the dept. of labour so please don't use this as a reference unless you know the code yourself) that double insulation is necessary.

From inside the concrete ceiling a roundbox is joined to a metal conduit by means of a domelid, through which a pair of live and neutral housewires (just 2 wires) feed a circuit of two lights via a screw connector (porcelain connector) join. It has the old system of no-earth wire. I'm not sure what that system is called,

Both light fittings (both are fluorescent) have surfix cable: light fitting one uses flat surfix, light fitting two uses round surfix with internal metal sheathing. Both use 1.5mm² conductor sizes.

Both lights have 230v (live and neutral connected). Only one light fitting works. Both light fittings do not have their earth wires connected.

Up the ladder, leaning on the cable tray with my arm, making full flesh contact and initiating cable disconnection, I make accidental contact with the earth wire coming from light fitting no. 2 (round surfix cable). I get a shock.

I test voltage between earth wire on cable from light fitting no. 2 to the cable tray: 95v.
I test voltage between earth on light fitting no.1 to the cable tray: 0v.

Light fitting no.2 is a fluorescent light fitting and is probably as old as the building, which I guess is 50 years. Maybe a fault in the light fitting?
I move the ladder underneath light fitting no. 2. I open the light fitting and it smells bad (burn smell). There are words like "condenser" and "W.A.C 275 and V.A.C 275" on one of the parts. I see a melted connector block next to the ballast. All the parts of the light fitting are assembled on the lid and almost knocked me out as it swung down cutting the last cable tie to release the lid.

I cut incoming live and neutral wires and tape the ends up. I leave earth wire connected to lid. I close the lid and head back to the round box join.
Reposition ladder.

I resume cable disconnection.

Shocked again! But the wiring is OPEN!?!

I test voltage:

Earth wire from light fitting no.2 to cable tray (cable tray is bonded fine all the way to the main DB): 90v.
Earth to mains neutral: 90v
Earth to mains live: 130v

I disconnect live and neutral.

With ALL wires going to the light fitting now open, I test voltage from incoming live wire to the light fitting wires:

Live to earth wire: 230v
Live to live: 230v
Live to neutral: 230v.

I change to continuity setting. I test continuity between the wires on the light fitting cable.

Live to Neutral: Clear
Live to Earth: Clear
Earth to Neutral: Clear

Insulation tester readings in the gigaohms values between all wires (earth now disconnected at fitting).

The cable is OKAY.

Please explain :)

My guess is a magnetic field generated is around the live wire, crosses into the metal sheathe, which in turn generates its own field, which in turn passes through the earth and neutral wires.
 
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What do you mean live to live 220 volt.
I ones had a sir-fix cable with a neutral dis inside off the cable.

Best is to make a drawing, and post it here. And these two fittings , are the same feed feeding both. While you are there, why not pull in a earth wire.
 
upup said:
What do you mean live to live 220 volt.
I ones had a sir-fix cable with a neutral dis inside off the cable.

Best is to make a drawing, and post it here. And these two fittings , are the same feed feeding both. While you are there, why not pull in a earth wire.
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upup said:
What do you mean live to live 220 volt.
I ones had a sir-fix cable with a neutral dis inside off the cable.

Best is to make a drawing, and post it here. And these two fittings , are the same feed feeding both. While you are there, why not pull in a earth wire.
Click to expand...
I mean between the disconnected wires:
voltage between live mains and live on cable going to light fitting no. 2 is 230v
 
Nope, Too complicated a reason. You have to find out why the tray is live.

If you are allowed/can, cut ALL power to the installation, check the tray for being live/ earth bonded/contact between Neutral.

Then start by bringing up circuits one by one until you measure the voltage on the tray and then trace that circuit causing the contact condition. it could be anywhere.
 
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Had similar issue with one of my properties, not an electrician so using plain English, no idea how they got their clearance before transfer, anyways, one of the aircon units had a permanent earth leak issue, earth wire was cut due to them switching to polycop pipes, in effect, house had no earth, there is a permanent amount of energy in the earth wiring which had nowhere to go, I just ran a wire from DB to original pipe in the ground, problem solved. I have feeling the earth leakage switch is damaged as well since that didn't trip, but I'm no electrician so what do I know.
 
Razer0 said:
My guess is a magnetic field generated is around the live wire, crosses into the metal sheathe, which in turn generates its own field, which in turn passes through the earth and neutral wires.
Click to expand...
Nah, that's a bit of a too wild guess.

Electrician here, thanks for the drawing but may I ask for a ruler drawn drawing with voltages measured indicated on the correct points and the condition of which it was found and measured
 
Did you do an insulation test between the metal conduit and the wires or only between the wires?
 
Kawak said:
Had similar issue with one of my properties, not an electrician so using plain English, no idea how they got their clearance before transfer, anyways, one of the aircon units had a permanent earth leak issue, earth wire was cut due to them switching to polycop pipes, in effect, house had no earth, there is a permanent amount of energy in the earth wiring which had nowhere to go, I just ran a wire from DB to original pipe in the ground, problem solved. I have feeling the earth leakage switch is damaged as well since that didn't trip, but I'm no electrician so what do I know.
Click to expand...
Current problem solved. Original issue still unknown, but much better now than before as there is a path to earth.

Easy to verify if the ELCB s working simple test.
The problem the Aircon also easy to find if someone wants to bother.
 
Geoff.D said:
Current problem solved. Original issue still unknown, but much better now than before as there is a path to earth.

Easy to verify if the ELCB s working simple test.
The problem the Aircon also easy to find if someone wants to bother.
Click to expand...

I will eventually get an electrician to fully check everything there, have great tenants in there for the past 4 years, at the time, I was just trying to get it in a rentable state, all just me figuring it out with my varsity physics 101 knowledge and youtube, got shocked when I touched the dishwasher with one hand and my other hand on the door frame, quite a strong shock as well.

At least my cable run and wifi is working super great in there. Probably not to code as I just used the same electrical conduits.
 
You probably have a direct earth fault somewhere in the house.

Put an amp clamp around the incoming cable from the munic. You're looking for a reading above 60mA. (Direct earth fault should be around 800mA-1A leak.)

Switch off every circuit one at a time until the leak disappears. That's your culprit. Then unplug every device and switch off every light on the circuit one by one until the leak disappears again. That's your faulty point. Fix it.

I had a 1A leak in my house that even tripped the neighbours' earth leakage protectors. Culprit was a shoddy plug connection behind the fridge. A single core of the cable touched the earthed socket.
 
Kawak said:
I will eventually get an electrician to fully check everything there, have great tenants in there for the past 4 years, at the time, I was just trying to get it in a rentable state, all just me figuring it out with my varsity physics 101 knowledge and youtube, got shocked when I touched the dishwasher with one hand and my other hand on the door frame, quite a strong shock as well.

At least my cable run and wifi is working super great in there. Probably not to code as I just used the same electrical conduits.
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You need an electrician there pronto dude. Not eventually. Dead tenants don't pay very well.....
 
gertvanjoe said:
Nah, that's a bit of a too wild guess.

Electrician here, thanks for the drawing but may I ask for a ruler drawn drawing with voltages measured indicated on the correct points and the condition of which it was found and measured
Click to expand...
WhatsApp Image 2021-06-24 at 07.01.25.jpeg
 
gertvanjoe said:
You need an electrician there pronto dude. Not eventually. Dead tenants don't pay very well.....
Click to expand...
Had a friend looked at it, it's currently safe, what needs to happen according to him is a big job to have the entire board changed, I wanted him to maybe also rewire the place to modern standards, the board has some rectangular blocks for fuses instead of trip switches. Current tenants don't want to move out for the job to be done so... they also kept extending contract, if they're happy, I'm OK.
 
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