insulation resistance is down...

[thomas123]

Hi guys,

I need some help, im doing a periodic on a building and when carrying out an insulation resistance test line to earth it reads as 0 on every circuit i tested, the circuits have neons and fluorecent fittings connected hence why i did line to earth. its doubtful that every circuit is down right? its wired in pvc/pvc singles.

Any ideas what i could be?

 

[matt.leung]

link Live and Neutral together and test to earth (cpc). this is what is meant by lives to earth...

 

[thomas123]

you can test line to earth and neutral to earth seperatly as well i thought?

 

[Zeespark]

Nope, and should you be doing Periodics if asking this question? (I am not meaning to sound nasty, you just seem a little out of your depth is all)

AndyGuinness

 

[matt.leung]

but there are still items connected to live and neutral, so u will get a OM ohm reading / result...

u need to link L&N together and test to earth for it to work...

 

[thomas123]

how would it make a difference? line to earth is still down.... by connecting line to neutral and then testing them to earth it would not make any difference..

out of my depth andy? you dont know me so you cant make that judgment..

just read my testing book, 2391 practical guide by christopher kitcher, i knew i was right.. it says that you can test live conductors to earth seperately...

 

[revjames]

out of my depth andy? you dont know me so you cant make that judgment..

I think Andy is just politely pointing out that the finer points of inspection and testing are usually covered in the relevant training courses. It does seem that you SHOULD know how to do this if you are qualified to do a periodic inspection.

 

[m4tty]

What was the answer then tommy mate?(ive got that book too its a gooden aint it)

 

[thomas123]

I think Andy is just politely pointing out that the finer points of inspection and testing are usually covered in the relevant training courses. It does seem that you SHOULD know how to do this if you are qualified to do a periodic inspection.

but i do? line to neutral would be down if a load is connected, but line to earth would not? my question is why?

---------- Post Auto-Merged at 21:52 ---------- Previous post was made at 21:49 ----------

What was the answer then tommy mate?(ive got that book too its a gooden aint it)

page 59 dude, does it or does it not say that you can test live conductors to earth separately lol, then some people on here are basically calling me incompetent? when i've clearly proved them wrong?

 

[matt.leung]

by pumping 500v down the conductor will damage the equipment connected to it.. if you test L&N together to earth, u r limiting the damage caused as well

 

[m4tty]

I'll have a butchers tomorrow matey as the books in the van with the rest of them and it's p1ssing down lol.

 

[thomas123]

by pumping 500v down the conductor will damage the equipment connected to it.. if you test L&N together to earth, u r limiting the damage caused as well

how is it any different when testing line to earth and neutral to earth? its the same as joining them together.............. is it or is it not? the damage is done when you test line to neutral..

 

[matt.leung]

no its not..

 

[thomas123]

no its not..

explain yourself then? it seems to me that your only repeating what it says in GN3? and you cant give me an explanation why?

 

[matt.leung]

i am not even openning up GN3, honestly i know what i am saying. by joining L&N together and test to E, u r limiting / stopping any damage to the item in question... if u test L to E, N to E, you need to disconnect the item, or u will get 0M ohm as a result...

how much testing experience do u have...

 

[Doc Hudson]

you can test line to earth and neutral to earth seperatly as well i thought?

just read my testing book, 2391 practical guide by christopher kitcher, i knew i was right.. it says that you can test live conductors to earth seperately...

If you are quoting correctly then that is a book who's advice I would treat with up most caution. Testing Line on its own to earth with sensitive electronic components still in circuit can damage those components if you stick 500v DC across them. That is why you test 'L+N' to 'E'

Doc H.

 

[m4tty]

By joining them together it bypasses the load doesn't it? That's what I was taught

 

[Sidewinder]

A 230V rated device is just that rated to 230V, if you stuff 500V wrt earth then you are putting an overvoltage on the device, there may be a clever unit somewhere on the circuit dumping the overvoltage as it is seen as a fault.

I don't know the install so I can't give you an exact answer!

Is there an rcb or an mcb protecting the circuit, are there em lights on it, are the lights switch start of hf, are there any discharge lights on the cct (i.e. other than "normal" fluoros?

This voltage will shifty down the live through the connected loads back up the neutral straight to earth hence your short, even if none of the above are true.

 

[Doc Hudson]

how is it any different when testing line to earth and neutral to earth? its the same as joining them together.............. is it or is it not? the damage is done when you test line to neutral..

By keeping both L&N at the same potential you cannot put excessive potential across the L&N of an electronic device. When you have seen an electronic central heating programmer fried due to incorrect insulation resistance tests then I think you may understand. It is not the identification of the low reading it will assist. It is purely preventing you from damaging the customer other accessories.

Doc H.

 

[batty]

Always test at 250 volt first and unless you are going to disconnect all the lighting only test live and neutral to earth that what I do anyway.