Continuity testing of CPC on lighting circuit

[600rob]

Hi,


I recently posted a thread about the necessary steps required to modify the wiring for a single halogen light fitting to allow me to fit a ceiling rose and install a conventional light fitting.


A couple of the members replied explaining the process which is fairly straight forward.


However there is one area that I’ve not done before and require some further advice as im not sure about how to do it.


I was advised to check the Continuity of the CPC/Earth.

Ive only performed continuity checks on various automotive/motorcycle circuits using my multimeter.

I had a search online and it seems a bit more involved for a lighting circuit

Firstly, is it possible for me to check the continuity of the earth on my lighting using my basic multimeter with a built in continuity buzzer or are specialist tools and knowledge required?

Secondly can anyone explain exactly what I need to do to test the continuity on my lighting circuit?

Also does the test need to be carried out for all the lights on the circuit or can the test be carried out locally at the light/junction box that will be changed?
During testing what sort of readings should i be looking for.

Cheers
Rob

heres the original thread if you need a reference to it

//www.diynot.com/diy/threads/c...ventional-light-fitting.449855/#ixzz3wMu30nv1

 

[EFLImpudence]

I was advised to check the Continuity of the CPC/Earth.
Ive only performed continuity checks on various automotive/motorcycle circuits using my multimeter.
I had a search online and it seems a bit more involved for a lighting circuit

Firstly, is it possible for me to check the continuity of the earth on my lighting using my basic multimeter with a built in continuity buzzer

Yes. If the meter will measure low enough values.

or are specialist tools and knowledge required?

Maybe a bit to interpret the results are as expected.

Secondly can anyone explain exactly what I need to do to test the continuity on my lighting circuit?

You will need a long lead from the location to the Main Earthing Terminal.
One probe to the light CPC and one to the long lead.
The result, after deducting the resistance of the long lead - previously measured, will be the resistance of the CPC.
Depending on the distance, the measurement should be near the expected.

If a lot higher, then you have a poor connection somewhere.

Also does the test need to be carried out for all the lights on the circuit or can the test be carried out locally at the light/junction box that will be changed?

That depends:
If it is the first light on the circuit, this will not verify the rest.
If it is the last, then it will.

During testing what sort of readings should i be looking for.

The usual 1mm² conductor has a resistance of 18.3mΩ per metre - 183mΩ per 10 metres.

Other sizes are proportionately different. For example 1.5mm² will be 18.3 ÷ 1.5

 

[600rob]

You will need a long lead from the location to the Main Earthing Terminal.

Is this the terminal located on the consumer unit?
If so my consumer unit is in the garage so ill need a super extra long lead

That depends:
If it is the first light on the circuit, this will not verify the rest.
If it is the last, then it will.

Not sure, id have to find out how to work out where the light is on the circuit

Im starting to think this task my be slightly above skill/knowledge level.

Would/should a professional spark carry out this procedure in the process of changing a halogen light fitting back to a conventional fitting with a ceiling rose?

I think it might be time for me to get a professional in to do this

 

[Taylortwocities]

If all you need to do is to check the continuity of the earth, then you can make the test from the earth connection of a nearby socket outlet.
It is usually not necessary to remove the socket itself as the metal securing screws are connected to earth, so you only need to touch your continuity tester on the screw to confirm the earth connection.

Always do tests like this with all the power completely off!

Would/should a professional spark carry out this procedure in the process of changing a halogen light fitting back to a conventional fitting with a ceiling rose?

Yes! The earth for the lighting circuit must be continuous from the consumer unit though to every light point, switch and on to the next light. This earth provides a fault path and will stop metal light fittings, etc becoming live if a fault occurs.
Professional sparks (and DIYers) should be carrying out proper tests on circuits before they are energised. One test (polarity) will confirm that there is a correct earth path. Just because the light comes on does not mean that it is installed safely, or correctly!

Here is how the polarity test it is done, properly. You do not need a very long lead if you do it this way.

 

[EFLImpudence]

Mmmm.

 

[Taylortwocities]

I'll name that tune…