Changing metal ceiling rose - weird cabling

[robert888]

Ok, so I'm changing a metal ceiling rose in my flat with a similiar unit and have come across something weird/dodgy.

When I disconnected the cabling I found a 3 core cable (black, red and one unsheathed). Black was connected to live, unsheathed was connected to neutral and red connected to nothing. Does this mean that my light has been running through earth all this time? In theory, should it 'work', albeit unsafely, like this (ie the light will still light without tripping a circuit breaker)?

Can I easily test with a test meter if the earth wire IS actually earth?

I will probably just get an electrician out but wanted to make sure I grasp what's going on here before handing over cash.

 

[PrenticeBoyofDerry]

It sounds very much like the the earth core/CPC (the bare conductor) has for some reason been used as the neutral.
Could be a few reasons for this: ignorance, laziness, stupidity or the neutral could have been damaged/broken/to short, so no continuity in the conductor. Then the idiot instead of repairing/replacing has used the earth/cpc conductor.
It will work! It has worked!
Not good practice and not recommended!
And considering the fitting is metal, the likelihood is that it will need to be connected to earth.
So get the cable replaced, if you don't feel confident that this is within your scope, do call an electrician, but be prepared, this could just be one of many problems, if you have had a nutty DIY persons pretending to be an electrician previous to your occupancy in the house. I hope it is not the case and was just one mad moment.

You can test for earth continuity, if you have a meter that will do this, ie continuity tester or multi-meter.
It will mean disconnecting all the conductors at the CU for this circuit and testing across the conductors.
You can do an R1+R2 test with phase and earth conductors linked up at the CU and then test across phase and earth at the fitting. The light switch should be closed/on
With your set up this should test clear but in reality you should get a low reading, this will depend on the length of the circuit.
You can also check for continuity of the neutral cable again by linking up with the neutral to the phase conductor at the CU and testing across them at the fitting, looking for a low reading.
Low readings normally are, something between zero and 2 ohms depending on length of the circuit and how close the light is in relationship to the CU.

Remember to identify circuit, safely isolate with an approved voltage tester and prove it is dead before you start any work.

 

[ban-all-sheds]

Robert - is that lighting circuit on an RCD?

 

[robert888]

Thanks for the input.

Yes, lighting circuit on an RCD.

 

[robert888]

Also, if I take the colours on the supplying cable literally, doesn't this mean my light has been running through earth (unsheathed) and neutral (black)? Would this still light? I thought it wouldn't as isn't neutral at approx ground voltage whereas live cycles from -230 to +230 V?

Time to call an electrician I think!

 

[ban-all-sheds]

Also, if I take the colours on the supplying cable literally, doesn't this mean my light has been running through earth (unsheathed) and neutral (black)? Would this still light? I thought it wouldn't as isn't neutral at approx ground voltage whereas live cycles from -230 to +230 V?

That you have an RCD means the circuit can't have been using earth instead of neutral.

Time to call an electrician I think!

Absolutely.

 

[PrenticeBoyofDerry]

As BAS says if this circuit is protected by an RCD the earth wont be connected to the neutral.
But that means the earth cable at that fitting is being used as a live conductor (neutral). Needs to be sorted out!

 

[EFLImpudence]

For future help -

NEVER ASSUME.

Also, if I take the colours on the supplying cable literally,

No such thing, you cannot tell by looking.

The wires SHOULD be sleeved with the appropriate colour to signify their actual use.

doesn't this mean my light has been running through earth (unsheathed) and neutral (black)? Would this still light?

No, it wouldn't.

However, if the other end of the "unsheathed' wire is connected to live then it wouldn't be 'earth'.

Wires can be used for anything - they don't know what colour they are.