Continuity and Polarity Test

[Jupiter01]

When testing a light switch that operates multiple downlights, do I need to test continuity and switch polarity at every downlight connector or can I do at the last downlight? Clearly, if there’s an issue at the last downlight, I can work backwards.

Thanks in advance.

 

[JohnW2]

When testing a light switch that operates multiple downlights, do I need to test continuity and switch polarity at every downlight connector or can I do at the last downlight? Clearly, if there’s an issue at the last downlight, I can work backwards.

'Continuity' of what - and what do you mean by 'switch polarity'?

Kind Regards, John

 

[Jupiter01]

'Continuity' of what - and what do you mean by 'switch polarity'?

Kind Regards, John

Sorry should have added more details.
I want to use my Megger MFT to do the Continuity tests and switch polarity test on a lighting circuit.

I want to test continuity of CPC and Line. I also want to test that the light switch is correctly operating the switch line to the light.

 

[JohnW2]

I want to test continuity of CPC and Line.

If the lights are working, there surely must be 'Line continuity', musnt't there?

As for the CPC, I think I would personally just measure the Zs. If you wanted to be sure that there was an effective CPC connection to eacg light, I suppose that, strictly speaking, you would have to do it at each and every light - although I suspect that many/most wouldn't bother (particularly if the lights were Class II )

I also want to test that the light switch is correctly operating the switch line to the light.

I think I'd just measure L-E voltage at a light with switch on/off. If all the lights were wired in parallel, you'd only have to do that at one.

If one switch (when 'off') is successfully killing the L-E voltage at one of the (connected in parallel) lights, then that should be good enough, even if there were 2-way (or N-way) switching, since if one were switching L and another were switching N, there would presumably be a big bang at some point!

Kind Regards, John

 

[Jupiter01]

f the lights are working, there surely must be 'Line continuity', musnt't there?

Nothing is energised yet. I wanted to undertake the necessary tests first. I understood that continuity of CPC and Line were the required tests. Along with IR testing. My Line is looped at ceiling. I was proposing to join CPC and Line in CU and then test at the Ashley Junction Box first. I can then test at the last downlight as there are 12 in total.

If all the lights were wired in parallel, you'd only have to do that at one.

I think my lights are wired in series.
My first downlight has an Ashley Junction box. This contains the Supply from the CU, cable from switch and cable that goes to downlight #2. Downlight #2 then has one that goes to downlight #3 and so on. The last downlight only has the one cable.
I was proposing that I test switch polarity at downlight #12 and if this is successful, I think it confirms that all others are correct too. That’s my assumption.

I suppose that, strictly speaking, you would have to do it at each and every light -

if I test at he last downlight and get a good enough low ohms reading, doesn’t this confirm that the other downlights also have continuity?

even if there were 2-way (or N-way) switching

Just the one switch in my case. In fact a dimmer.

 

[Harry Bloomfield]

If lights are daisy chained, then to be thorough, you would need to verify polarity at every single out let - reason being that the cable polarity could be reversed at one fitting, then reversed again at subsequent fitting, the net result being the correct polarity at the final fitting in the daisy chain.

 

[ericmark]

I think my lights are wired in series.

I hope not.

However MR16 does cover many types of down light, and could include SES, but in the main it does not matter if the lives are swapped, only with screw lamps must the line go to centre.

Getting wires swapped can be like a virus working its way through a site, yellow and blue (now black and grey) being swapped many times, and there is a good reason for using a phase rotation meter to ensure correct rotation, but with single phase all that really matters is that any single pole switch is in the line not the neutral, and screw lamps centre is line, for lights, sockets the same, need to ensure the fuse and if there is a switch also the switch is in the line not the neutral.

But G5.3, GU10, BA22d etc, it does not really matter, so why test?

 

[Jupiter01]

If lights are daisy chained, then to be thorough, you would need to verify polarity at every single out let - reason being that the cable polarity could be reversed at one fitting, then reversed again at subsequent fitting, the net result being the correct polarity at the final fitting in the daisy chain.

I am using the blue click connectors for the downlights. Can I visually inspect (they are transparent) that polarity is correct for all intermediate downlights and then just test at the last light?

 

[EFLImpudence]

Can I visually inspect (they are transparent) that polarity is correct

No.

Checking polarity is not just making sure you have put the brown and blue wires in the right place.

It is checking that the correct wires are actually the line conductor and the neutral or if you can't see the wires that, for example, the socket holes are the right way round.

 

[JohnW2]

Nothing is energised yet. I wanted to undertake the necessary tests first. I understood that continuity of CPC and Line were the required tests.

Fair enough. If not energised then you obviously have no alternative but to doi it by continuity of L snd CPC (and, I suppose, theoretically also of N).

I think my lights are wired in series.

As has been said, you have the terminology wrong. If they were truly in series, each lamp would only get a fraction of the supply voltage (a quarter of supply voltage in this diagram) ..

I was proposing that I test switch polarity at downlight #12 and if this is successful, I think it confirms that all others are correct too. That’s my assumption. if I test at he last downlight and get a good enough low ohms reading, doesn’t this confirm that the other downlights also have continuity?

I suppose one could argue that, if you have just installed the entire circuit, and therefore are certain that you know exactly how the wiring has been undertaken, that would be sufficient. However, in any other situation (i.e. if any of the circuit was pre-existing),then I think you would have to test at every single light, since you couldn't be sure how anything was wired (e.g. some lights might be supplied via hidden JBs, which could have faults/errors).

Kind Regards, John

 

[Taylortwocities]

Simply follow the method described in your OSG, or GN3.
It describes exactly how to carry out the continuity/polarity tests on a lighting circuit.

 

[Jupiter01]

One more on this please.
When IR testing a lighting circuit, I understand we need to repeat the IR test after changing the switch position from where it was in the initial test.

If the lighting circuit being tested has multiple switches, does the above mean that you do an initial IR test and then change switch position on every switch and do one more test or do you have to change switch positions one at a time and repeat the IR test for each switch position change?

 

[scousespark]

As this is a new circuit, have you notified your LABC?
As for the post, the OSG tells you the steps to follow.
You still don't seem interested in understanding any of the underpinning theory.

 

[Jupiter01]

As this is a new circuit, have you notified your LABC?
As for the post, the OSG tells you the steps to follow.
You still don't seem interested in understanding any of the underpinning theory.

The above understanding is from the OSG @scousespark. I’ve not plucked this out of thin air!
I am not an electrician and have had to learn this. I am asking questions where things are unclear or I require validation.

I have a local electrician that provides a certificate for my work. Yes, he will only sign it off once he can understand the design and is shown the pictures, etc. and of course, is ultimately happy with the installation. His last comment was that my work is better than most “electricians” work he has seen

On the past two occasions, his test readings have been exactly the same as what I have done on my Megger MFT. I wanted to do the same again.

 

[davelx]

"The above understanding is from the OSG @scousespark"
It's clear to me that you don't understand what the reasons for doing the tests are and what the results tell you, you only understand that certain tests need to be done. You need to understand WHY these tests are needed and what the results show. If you had a basic understanding of how electric circuits work, say GCSE physics level, you would be able to deduce the answers to very many of your questions yourself. This would also aid you immensely in understanding what testing is all about and why it is done in a certain way.

On a simple one-way lighting circuit with a single switch, why do you think it is necessary to to the insulation test with the switch in both positions?