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

E

Ellsa100

DIY
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!
 
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James said:
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
Click to expand...

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!
 
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James said:
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!
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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
 
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Ellsa100 said:
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
Click to expand...

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
 
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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
 
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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
 
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Ellsa100 said:
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.
Click to expand...
what right minded spark told you that ,or i sould say a clown spark .
 
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radiohead said:
Think I've heard it all now.......By the way anyone know if I can use the gas pipe for my shower feed?
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only if it's a gas shower.
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buzzlightyear said:
what right minded spark told you that ,or i sould say a clown spark .
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OPsaid a builder told him... nuff said.
 
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Ellsa100 said:
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)!?
Click to expand...
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.

Ellsa100 said:
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)?
Click to expand...
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.
 
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thanks very much for your comments. i'm gonna get a registered electrician in to look at things. May also get a once over for all the wiring for peace of mind too, but i do appreciate learning things (and need to know my limitations lol).
 
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When manoeuvring the one light fitting you have moved the cables.

This in turn has highlighted a poor termination at elsewhere that has failed.

Two things a proper electrician would have ensured.

1, All terminations are secure.

2, Where practicable cables are clipped so as to relieve stresses.


How many of these lights are in this room?

How many are still working?

There's a good chance the loose neutral lies in the last working fitting = easy fix, or in a junction box = pain in the proverbial.
 
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GBDamo said:
When manoeuvring the one light fitting you have moved the cables.

This in turn has highlighted a poor termination at elsewhere that has failed.

Two things a proper electrician would have ensured.

1, All terminations are secure.

2, Where practicable cables are clipped so as to relieve stresses.


How many of these lights are in this room?

How many are still working?

There's a good chance the loose neutral lies in the last working fitting = easy fix, or in a junction box = pain in the proverbial.
Click to expand...

Thanks - there are 5 lights in the bathroom. 4 lights are not working. OMG you made me realise what is wrong with the circuit!!!! I checked the one light that is working - and the other lights are working parallel off that - and the neutral there had come out. Hey presto!!!!!!!!!! pushed the neutral back in and now all 5 lights are working. thank you so much!!!
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Ellsa100 said:
Thanks - there are 5 lights in the bathroom. 4 lights are not working. OMG you made me realise what is wrong with the circuit!!!! I checked the one light that is working - and the other lights are working parallel off that - and the neutral there had come out. Hey presto!!!!!!!!!! pushed the neutral back in and now all 5 lights are working. thank you so much!!!
Click to expand...

I find the junction boxes can get so busy with wiring that wires can flick out of their termination points when you try to squeeze everything in....
 
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I find the junction boxes can get so busy with wiring that wires can flick out of their termination points when you try to squeeze everything in....

that's why wagos are best thing since inside bogs.
 
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telectrix said:
I find the junction boxes can get so busy with wiring that wires can flick out of their termination points when you try to squeeze everything in....

that's why wagos are best thing since inside bogs.
Click to expand...
I'm tempted to go round putting the original junction boxes - which seem way more secure and spacey - than the small ones that came witht he light fittings, just to stop this issue happening again.
 
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telectrix said:
I find the junction boxes can get so busy with wiring that wires can flick out of their termination points when you try to squeeze everything in....
Click to expand...
You do love your wago's don't you Tel :D
I'd have to agree though. I started electrics at around the time wago's were coming out so that's what I've mainly used. However, I come across screw junction boxes all the time and by golly they're a pain in the backside when you've got a few cables to get in.
The screw/bolt often doesn't go in straight.
It can take bloody ages.
Terminations come loose over time.
The lids often seem to be broken or not attached well.
Holes in the side where they have not been fitted properly.
If there's a few conductors in one terminal you're not completely sure they are all in properly as it's a right jumble.

On the plus side, on the very rare occasion when you have to hide a connection under a kitchen wall cabinet they come in handy :D
 
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happyhippydad said:
The OP clearly has DIY by their name which justifies asking this type of question.
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Right ok, Next we’ll have someone asking about a Flux capacitor. I know it’s got DIY by her name mate. But sometimes I often wonder the legitimacy of these posts.
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How childish a dislike... Opinions differ. Maybe Chris has a point about soft women on this site.
 
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I have given out over 2000 likes and agrees
Just 12 dislikes.
I have no interest in getting in a debate about it but I do actually dislike the post.
 
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The first test is a continuity test followed by the earth impedance test.


the continuity test would show that the earth is connected to the house earthing system but would not show if it was safe from cutting the electricity in the correct time.

if you assume that there is no secondary fault, you could do this using the earth at the light with the earth in a socket or even the water pipe .

I and others I know have fitted a wire to the earth pin in a plug (no live or neutral) and use this as an earth point for comparison.
 
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Ellsa100

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If you're a qualified, trainee, or retired electrician - Which country is it that your work will be / is / was aimed at?
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