230v on disconnected ring neutrals

[DaveS]

Hi all

Hope everyone enjoyed wknd. My day been spent trying to get head in testing books to prepare for exams. Not got much testing experience so trying to make most of time and testing a few circuits I indoors. Probably missing something really obvious but this bothering me a bit. When testing ring circuits and I have isolated and have neutrals disconnected why exactly is it that when testing between these neutrals and live terminals of any other circuits I still have a 230v potential? and this reduces to 150v when all switches turned off. I can only think that this is because I'm getting an earth potential through neutrals but where exactly is this happening if neutrals disconnected at board? Thanks

 

[Sintra]

Hi all

Hope everyone enjoyed wknd. My day been spent trying to get head in testing books to prepare for exams. Not got much testing experience so trying to make most of time and testing a few circuits I indoors. Probably missing something really obvious but this bothering me a bit. When testing ring circuits and I have isolated and have neutrals disconnected why exactly is it that when testing between these neutrals and live terminals of any other circuits I still have a 230v potential? and this reduces to 150v when all switches turned off. I can only think that this is because I'm getting an earth potential through neutrals but where exactly is this happening if neutrals disconnected at board? Thanks

If you are practicing for exams then I would advise that you start out with safe isolation as your first step. Why exactly are you testing between these neutrals and lines from other circuits.

 

[Darkwood]

Please list your sequence of isolation, testing and results - it gives us a chance to see why you are getting these readings.

 

[telectrix]

you're probably getting a false reading. the N is floating. if you look at a MK external light switch, you;ll see that the neon is across L and S/L. it works when the switch is in the off position. idea is to find switch in the dark.

 

[DaveS]

If you are practicing for exams then I would advise that you start out with safe isolation as your first step. Why exactly are you testing between these neutrals and lines from other circuits.

I have Safely Isolated with locking devices and also labels for the sake of good practice. I tested between these disconnected neutrals and lives of other circuits to make sure that i had disconnected correct neutrals. My thinking is that if i had disconnected correct ring neutrals surely there would be no voltage present. Is there another way of checking this? I have since attempted same tests to check there is not something i am missing. I definately have correct ring neutrals as i am getting continuity across them. I decided to test voltage with my di logic voltage indicators instead and these give a neglligible voltage about 24v but when i use Kewtech KT65 Multitester i am still getting 240v Still bit baffled about this and doesnt give me great faith in my new testers if not giving me correct voltage readings??

 

[PEG]

Hi Dave,the test for finding a link between those disconnected neutrals and anything else,is an IR test. You would not test between them and another live circuit as this will give all kinds of results especially with a digital MFT. The variation of voltages you have observed is probably as a result of the differing loads the various meters apply. Remember,you will get a voltage across a wet hair to live,with these digital yokes. Just go through the standard test procedure,including checking for any parts of the circuit vulnerable to the test applied.

 

[DRG]

What exactly do you have isolated mate, the whole installation or just the Ring Final Circuit you're testing on?

It's hard to say since you have two conflicting test meters and results but if you are doing this from inside the DB are you sure you haven't disconnected the neutrals from another rfc which is still energized and therefore broken the circuit giving you the 240v? It can be quite tricky to find the correct legs especially in a busy/untidy board and this would still give you continuity on N-N as you would just be mistakenly doing continuity test on the wrong ring.

You could maybe try and R1+RN to ensure you have a correct ring and no connections to other circuits (just "spit-balling" off the top of my head here)

 

[PEG]

Hi Dave,you are probably not still pondering your "strays",but i remembered a good method of demonstrating what i think you are finding. If you get yourself a new drum of cable,t+e in 1.5 or 2.5,ensure the end is visible and the cores are separate.Strip the free end cores and IR test between all conductors,which should reveal an excellent reading.Now connect (safely),the free end to line and neutral.Now,using your MFT,measure for a voltage between the unconnected cpc and the neutral.Test that cpc with a neon,it will indicate. Now,at this stage,re-test with your IR meter just to prove no connection between the cores. When the trainee then turns to receive the reason why this occurs,if not grasped,it is better to then say that all the results and readings are there...get reading (googling now i accept...) because wisdom learnt is ten times wisdom told...