Insualtion resistance testing.

[Patrick Griffin]

Hi lads,

When IR testing at a board I know i should expect a very high resistance between lives and earth but in a tncs system would i get a lower IR reading testing between N-E? The scenario im describing is one in which the tails are all connected but the board is isolated.

Cheers..

 

[Geordie Spark]

Industrial electrician? I don’t believe that for one minute after reading your posts.

You're still awake then???

 

[IzzyS]

when im doing the insulation tests i always isolate the board and disconnect the earth whilst doing the tests , this eliminates any connection for instance if the isolator is single pole , shouldn't be but possible in the case of switch fuses three pole isolators on three phase boards etc

Have a look at 612.3.1 The test should be conducted with the means of earthing connected, be it the supplier's earth, or a local electrode. Otherwise you could have a fault to true earth e.g. a bit of a steel framed building, and it wouldn't show up in the test.

 

[Plonker 3]

Have a look at 612.3.1 The test should be conducted with the means of earthing connected, be it the supplier's earth, or a local electrode. Otherwise you could have a fault to true earth e.g. a bit of a steel framed building, and it wouldn't show up in the test.

I read that as, between live conductors and any cable that will be connected to the earthing arrangement, not between live conductors and the MET as you imply.

 

[Guest77]

forgive me if im being thick here. .

Nope, consider yourself dismissed

 

[Patrick Griffin]

Tony i dont have a massive amount of experience, i was just asking a question why you would even go to effort to type a reply like that is beyond me.

 

[Knobhead]

Industrial electrician covers a very wide field. Which is your part of the field?

 

[Patrick Griffin]

Mostly panel manufacturing for motor control. Did commercial work too in new zealand. And bits of domestic here and there.

 

[Knobhead]

So who tests these panels if not you?

More to the point do you actually know how they work or is it glorified dot to dot wiring?

 

[Patrick Griffin]

I understand well. Testing is done with the boss. Testing domestic, commercial boards i have not done i understand these for the most part bar a few areas one of which i asked in this thread.

The confusion with this thread is i forgot that in the uk you have double pole isolation i was assuming it was like here in ireland where you have single pole isolation. I just wanted confirmation that the neutral or earth has to removed to break the n-e link in the tncs system.
Parts of this type of testing i had forgotten so i decided to started reading up on it and asking questions on this forum, it has been great until now.
Goodluck tony and thanks.

 

[IzzyS]

I read that as, between live conductors and any cable that will be connected to the earthing arrangement, not between live conductors and the MET as you imply.

It wasn't my intention to imply the test is between the live conductors and the MET.

The test should be conducted "between live conductors and earth". Note that it does not say cpc) "Earth" has a very specific meaning in the regs. To perform the test properly, and to obtain a valid result, there must be a connection to "earth" at the time of test.

A nail through the line conductor only, into damp plaster, won't show up if the test is carried out with no cpc connection to earth, but it will show as low IR if the test is carried out between line and "earth" i.e. cpc connected to MET, assuming a valid means of earthing.

 

[Risteard]

when im doing the insulation tests i always isolate the board and disconnect the earth whilst doing the tests , this eliminates any connection for instance if the isolator is single pole , shouldn't be but possible in the case of switch fuses three pole isolators on three phase boards etc

The cpc should not be disconnected. The means of earthing should be intact before conducting the test.

 

[Risteard]

I think i failed to mention im from ireland and we use a single pole switch fuse on our boards and in the uk you guys use a double pole. So without the main earth disconnected the N-E link would still exist for me.

Thanks for the replies lads!!!

The main Neozed switch fuse?

 

[ChrisElectrical88]

no because when you carry out an IR test on the whole board the isolator should be off or if individual circuits are tested live neutral and earth should be disconnected

The earth should always be connected to the MET mate

 

[shanky887614]

your supposed to remove all cables during ir test anyway, at same time as r1+r2 etc.

isolate supply and remove incoming during ir of you want to do a global then

 

[shanky887614]

The earth should always be connected to the MET mate

not when doing a ze though because you will get false readings