No voltage on live-neutral but voltage on live-earth

[Ellsa100]

Hi there

I recently replaced the downlight fittings in my bathroom so they are now GU10 LEDs (previously they were MR16s). The lights are IP65 and connected to a 30mA RCBO.

The light was working fine until recently. I was fiddling with the light fitting to correct the ceiling which had been damaged in the swap over - which involved taking out the fitting and replacing it - and now the LED isn’t working. I used a multimeter to check the voltage and there is 240v between live and earth but 0v between live and neutral. It seems like the neutral has been disconnected somehow.

The wiring is difficult to access as It is in the ceiling void - so it would be tricky to figure out the issue with the neutral wire. Would it be OK to use the earth wire to complete the circuit given thedownlight is double insulated?

thanks!

 

[James]

ABSOLUTELY NOT OK TO USE THE EARTH.

You need to repair the break in neutral conductor or get someone in to do it for you.

It is a fundamental safety issue and is not negotiable

 

[Ellsa100]

Thanks. I thought so but wanted to check.

ABSOLUTELY NOT OK TO USE THE EARTH.

You need to repair the break in neutral conductor or get someone in to do it for you.

It is a fundamental safety issue and is not negotiable

 

[James]

ABSOLUTELY NOT OK TO USE THE EARTH.

You need to repair the break in neutral conductor or get someone in to do it for you.

It is a fundamental safety issue and is not negotiable

Thought I might get the odd agree on this one.
First person to give me a disagree or thumb down gets laughed out of town!

 

[Ellsa100]

Thought I might get the odd agree on this one.
First person to give me a disagree or thumb down gets laughed out of town!

Here’s another question - how do I know earth wiring is properly earthed? I ask this as I have connected lots of earths using push in junction boxes for my GU10 fittings (the GU10s only need live and neutral but there were earth cables in the fittings and I know I need to keep the earth circuit), but how can I be sure the earth connection is good? The reason I ask is that I figured out there was a beak in the neutral only because the light wasn’t working and I then checked the voltage. But how would I check earth is complete circuit? Thanks

 

[Strima]

First person to give me a disagree or thumb down gets laughed out of town!

I'm Sorely tempted...

 

[buzzlightyear]

Thought I might get the odd agree on this one.
I being a person to give me self a
disagreement or thumb down gets laughed out of town!

Yea I agree what you say all day. Lol.

 

[radiohead]

Think I've heard it all now.......By the way anyone know if I can use the gas pipe for my shower feed?

 

[James]

Here’s another question - how do I know earth wiring is properly earthed? I ask this as I have connected lots of earths using push in junction boxes for my GU10 fittings (the GU10s only need live and neutral but there were earth cables in the fittings and I know I need to keep the earth circuit), but how can I be sure the earth connection is good? The reason I ask is that I figured out there was a beak in the neutral only because the light wasn’t working and I then checked the voltage. But how would I check earth is complete circuit? Thanks

You need a device called an earth loop impedance tester, ( loop tester for short)

It passes a current round the loop from live to earth and calculates the resistance.
This is an expensive piece of equipment that is not normally found in a diy toolbox

 

[Ellsa100]

1. Thank you to all the helpful and constructive replies.

2. When I explained my original issue to a builder (who holds himself out as a qualified electrician) - that on the downlight that wasn't working there was a voltage between Live and Earth but no voltage between Live and Neutral - it was his suggestion that I use Earth instead of Neutral to complete the circuit. This didn't seem correct to me - as I appreciate Earth wiring is an important safety requirement - which is why I wanted to ask the forum. I thought, maybe, because there was only one Earth wire connection to the downlight - i.e. there was not an Earth in and Earth out, just an Earth in - and the downlight was double insulated, maybe, just maybe, it was OK to use the Earth in place of the Neutral to complete the circuit (plus other GU10s which are connected in parallel to this light do not have any earth wiring, only live and neutral). But, as I said, it didn't feel right so I thought I should ask this forum. While I get the question I asked is probably a very stupid question, some of the replies mocking the question are not very helpful...

3. I assume running an earth loop impedance tester to check earthing of devices in my house is something left to the experts (i.e. I shouldn't buy a device off eBay and do it myself)!?

4. Last stupid question...why can't you just use a regular multimeter reading to check the voltage between a Live and Earth wire to check if it is grounded (i.e. if it reads 240v, it is presumably grounded, if it reads 0v, it is not)?

Thanks again for constructive comments!

E

 

[Mark Wright]

Your Electrician? is breaking the Regs if he was in court he could be in serious trouble.

I don't know what anyone else thinks but I might say he's breaking EAWR and that's statutory.

 

[radiohead]

Using a multi meter to check for earthing will only verify that there is a potential difference between the two points being tested.
Earthing conductive parts is to prevent the conductive part becoming 'live' in the event of an unexpected fault. As the earthing system is expected to be at zero volts, a fault current can flow, the magnitude of the fault current will depend on the impedance of the earthing system.
For example if the earthing system has an impedance of 1 ohm, the maximum fault current will be 230a on a 230v system.
The magnitude of the fault current determines how quickly the protective device operates and disconnects the circuit, preventing a shock or fire risk.
This is why the impedance of the earth fault loop path is measured with a sophisticated Earth Loop Impedance Tester, the result enables us to determine that the protective device in use..(fuse-MCB-RCD)...will operate within the maximum permitted time in the event of an earth fault, usually 0.4s
A multimeter cannot determine that

 

[littlespark]

Typical builder response.

and that’s why lighting circuits now need an rcd under 18th regs

 

[Mark Wright]

Not just that but obviously anything connected to a CPC and even the MET will become live when the Light is on - an RCD should trip anyway if someone does this.

 

[radiohead]

Typical builder response.

and that’s why lighting circuits now need an rcd under 18th regs

I'm not sure the IET's intention was to enable stupidity to be safely carried out.

 

[buzzlightyear]

When I explained my original issue to a builder (who holds himself out as a qualified electrician) - that on the downlight that wasn't working there was a voltage between Live and Earth but no voltage between Live and Neutral - it was his suggestion that I use Earth instead of Neutral to complete the circuit.

what right minded spark told you that ,or i sould say a clown spark .

 

[stevethesparks]

Get a qualified electrician in

 

[telectrix]

Think I've heard it all now.......By the way anyone know if I can use the gas pipe for my shower feed?

only if it's a gas shower.
[automerge]1593858685[/automerge]

what right minded spark told you that ,or i sould say a clown spark .

OPsaid a builder told him... nuff said.

 

[buzzlightyear]

Think I've heard it all now.......By the way anyone know if I can use the gas pipe for my shower feed?

only if it's a gas shower

wow ,whistling shower ,quick patient it and get it on dragon death .lol .

 

[pc1966]

3. I assume running an earth loop impedance tester to check earthing of devices in my house is something left to the experts (i.e. I shouldn't buy a device off eBay and do it myself)!?

If you are doing live testing on a high energy system (like the mains, where you have the prospect of a massive fault current) you really want to know that your equipment is safe and not going to explode in your face if something goes wrong. Buying stuff of eBay, more so if you do not know exactly what you are doing, is not a route to that goal.

The typical Multi Function Tester that would do this is in the £500-1000+ price range when new, so even 2nd hand (if working...) is going to be more expensive than getting a sparky in to do the work.

4. Last stupid question...why can't you just use a regular multimeter reading to check the voltage between a Live and Earth wire to check if it is grounded (i.e. if it reads 240v, it is presumably grounded, if it reads 0v, it is not)?

It is not a stupid question, in fact it is a subject that often catches out trainee electricians and similar. A typical digital multimeter has an impedance of 10M ohm, so to get a reading of 240V when the supply is 241V (a difference most would ignore as implying any sort of error in the circuit) only needs 24uA through the meter.

If the impedance to the real 0V point is less than 41.7k ohm you won't see anything wrong. Depending on how a cable is used and any interference filters connected to it, etc, you can get comparable levels of current flowing between insulated conductors via capacitance.

But if there really is a fault then 41.7k will only cause 5.8mA to flow, that will not trip any normal (domestic) protection system. But then the metalwork is live and if someone were to touch that and another potential they may get a serious or fatal shock.

Also you must remember that a 30mA RCD is there to provide "additional protection" and you don't really want to rely on it saving your skin as the 1st defence. RCDs have much higher complexity that then typical MCB over-current trip that ought to go in a fault and so a higher chance of failing, also most folk do not regularly test them (using the test button) so any fault could be present for years. Even a non-fatal shock can lead to serious or even fatal injuries if, for example, it leads to someone falling off a ladder.