Insulation Resistance Test One or Two?

[andyb]

Well there will be some current, but for a resitance of 1M ohm @ 230V it would be around 0.23mA @ 230V.

Even with a resistance of 7667 ohms @ 230V you would still only have just 30mA flowing (just enough to trip your RCD).

That's not the point.
If you know the resistance was 1M there would be no need to test anyway.
You are testing for lower readings than 1M, plus the fact that a lot of IT equipment uses the earth path and you do not want to be putting 500v across it.

 

[pevvers]

By the way I am booked on the NICEIC Virtual Reality PIR course later this month.

It's a very good course, I was invited on the pilot back in November. It's nice to see things from their eyes, and to see how they want you to test and certificate, and you will come away knowing that 99% of certificates are filled out incorrectly....

It's good fun too, like Doom but a bit slower!

 

[andyb]

I had an issue recently with some very minor work in a kitchen.
The pro forma minor works certificate shows IR as an essential test - which I didn't want to do because of neons/no acccess behind appliances etc etc.

I think I will use the LIMS more in future - and only do a 500v test if I get very poor readings on the 250v test 2.

Colonel, this post is about PIRs,
Any work you do must be tested accordingly and insulation resistance should be tested @ 500v.

Also, if you get a poor reading with 250v then you should investigate further before putting 500v to the circuit.

 

[pevvers]

That's not the point.

Well there is a point isn't there, if he says there's no current when there is?

You would not be putting 500V across the equipment if line and neutral are connected together!! I did 175 domestic PIR's a few years ago, used test 2 at 500V every time, with EVERYTHING plugged in. If I had broken something I'm pretty damn sure I would have known before I left the house. This is why we use the 2nd test in periodic situations.... I would happily stand there in front of you and megger my own house at 500V that way with computers plugged in all over the place just to prove a point.

 

[andyb]

Well there is a point isn't there, if he says there's no current when there is?

You would not be putting 500V across the equipment if line and neutral are connected together!! I did 175 domestic PIR's a few years ago, used test 2 at 500V every time, with EVERYTHING plugged in. If I had broken something I'm pretty damn sure I would have known before I left the house. This is why we use the 2nd test in periodic situations.... I would happily stand there in front of you and megger my own house at 500V that way with computers plugged in all over the place just to prove a point.

612.3.2 of brb

Where surge protection devices (SPD) or other equipment are are likely to influence the verification test, or be damaged, such equipment shall be disconnected before carrying out the insulation resistance test. Where it is not reasonably practicable to disconnect such equipment (e.g fixed socket-outlets incorporating an SPD), the test voltage for the particular circuit may be reduced to 250v dc, but the insulation resistance shall have a value of at least 1M.

Testing your house @ 500v proves no point at all, neither does the fact that you tested 175 installations @ 500v (so have I)

The op was asking why you can use 250v in some instances, that is the answer.

 

[pevvers]

612.3.2 of brb

Yes mate, I am aware of the reg. It's just that I have found that at 250V it's not always possible to identify problems, and so therefore devalues doing it a bit. The same can be said for connecting line to neutral and testing to protective earth as well. But if you do both in same test then this maybe isn't going to show up a fault.

I know everything has gone a bit off topic, so I apologise for that!

If there was an earth fault 500v could flow through the equipment to earth.

BTW, volts don't flow....

 

[andyb]

Yes mate, I am aware of the reg. It's just that I have found that at 250V it's not always possible to identify problems, and so therefore devalues doing it a bit. The same can be said for connecting line to neutral and testing to protective earth as well. But if you do both in same test then this maybe isn't going to show up a fault.

I agree and if anything at all shows up then further investigation is needed
Also testing with 250v is very rare, I can't remember the last time I needed to do it (you can usually isolate things for a shoet period)

BTW, volts don't flow....

Damm!!!

 

[pevvers]

Damm!!!

I'm glad you've got a good sense of humour!

I'm gonna leave this topic now as I think it's done, see you on the next one,