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..

 

[Plonker 3]

What are the actual readings you are getting when doing a IR test?

 

[PEG]

Hi dude,and how is a board which is isolated from a tncs supply,different from a board isolated from another type of supply?:stooge_curly: (smilie supplied as proof of not ribbin')

 

[nickblake]

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

 

[Clive P]

Hi,

Wot thy say^^^. ( always wanted to do that ).

Regards.

 

[Patrick Griffin]

Hi Dillb, i am an industrial electrician i was only asking the above question out of curiosity as i am trying to learn as much as i can about testing and different scenarios.

Hi PEG, forgive me if im being thick here. In tncs system the incoming earth is linked with the neutral. When the board is isolted this connection still exists. It a tt system no such connection exists.

 

[Plonker 3]

Any electrician should know about testing regardless of what sort of Installs they do.

As for the connection it will only exits it's if you have isolator that doesn't switch the neutral or a faulty switch, which is why the connection between the N-E would still exisist so you should always disconnect either the neutral or earth to carry out a IR test.

 

[Patrick Griffin]

Hi nick,

Thanks for the reply. I know the entire installion is to be isoted when performing an IR test. Does this include disconnecting the main earth for the board?

 

[nickblake]

Hi Dillb, i am an industrial electrician i was only asking the above question out of curiosity as i am trying to learn as much as i can about testing and different scenarios.

Hi PEG, forgive me if im being thick here. In tncs system the incoming earth is linked with the neutral. When the board is isolted this connection still exists. It a tt system no such connection exists.

only at the cut out the neutral will be isolated when the main switch is switched off so the out going of the board to the circuits will be disconnected from the Neutral earth link

 

[Plonker 3]

You only need to safely isolate the circuit you are working on, no as I said you only need to remove either the neutral or the earth as they will then be no physical connection between them.

 

[Flanders]

If you have a double pole switch single phase or 4 pole switch for 3 phase then the neutral will be disconnected are you talking about a 3 phase supply with a triple pole switch ?

 

[nickblake]

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

 

[Patrick Griffin]

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!!!

 

[davesparks]

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

There should be a neutral disconnect link in any 3pjase gear, usually a small metal link screwed or bolted in a kind of keyhole/sliding arrangement.

 

[Knobhead]

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