Insulation Resistance Testing Am2 - requires to be tested twice

sheppy619 · Aug 16, 2023

Hi,
I'm a little confused confused is someone can shine some light on the amendment 2 way of doing IR.
I know you have to do one 1st fix at 500V DC and then final one at 250V DC when all cables.
What I'm confused about is GN3 states:

"...sometimes these cables are terminated without further testing. This is no longer acceptable: it is now essential to test the protective conductor (such as armouring) with this connected via a fly-lead if necessary. To the installation earthing arrangement."

In other words it means IR testing the lines conductors clamping to the Banjo. The banjo will need a temporary connection to the MET for test purposes. (fig 2.23 shows an example of that)

Does that mean steel containment conduit will require this as well as its not specifically mentioned neither its used as a protective conductor.

Thanks people!

timhoward · Aug 17, 2023

sheppy619 said:
Does that mean steel containment conduit will require this as well as its not specifically mentioned neither its used as a protective conductor.

IMHO the principles are

1 - Sensible testing during installation e.g. making sure singles in steel conduit are not damaged and in contact with the containment, or the conductors in MICC are not breaching the outer copper core

2 - Mandatory 500v tests prior to loads / accessories being fitted with everything that is going to be earthed and bonded connected to the earthing system. This includes the armour of SWA, or steel trunking or conduit. Usually glanding into the switch gear and fitting banjo's / earthing nuts will achieve this.

3 - Mandatory final 250v tests when 2nd fixed.

For the mandatory IR tests to be valuable the earthing system needs to be completely intact. It can sometimes create challenges but we always find a way don't we!

sheppy619 · Aug 17, 2023

Ahh, I see so in other words your saying on your no.2 point.
Connect the CPC earth and fly lead bonding of the steel conduit to the earthing arrangement. (using wander lead maybe)
Then test at 500vDC

Thanks it has cleared it the way you said it.

pc1966 · Aug 17, 2023

The reason for testing with all the CPC & metalwork to the MET is to catch a situation like T&E with one of the live conductors nicked by a screw. If you test L-CPC alone (with CPC floating) that might be perfectly good if the screw has not breached both and you would not see the fault.

However, with the CPC to the MET and thus to the Earth at large (and hence now to the screw) there is a good chance you will see the fault as a suspiciously low IR for brand new cable, more so if you see something like >299M for N-CPC and, say, 10M L-CPC, then something is clearly not right even though at this point it actually passes the usual thresholds, etc.

davesparks · Aug 17, 2023

sheppy619 said:
Ahh, I see so in other words your saying on your no.2 point.
Connect the CPC earth and fly lead bonding of the steel conduit to the earthing arrangement. (using wander lead maybe)
Then test at 500vDC

Thanks it has cleared it the way you said it.

I can't see a need for any wander lead or temporary connection for IR testing, what do you think needs a temporary connection?

All of your conductors should already be connected by the time you do the testing.

sheppy619 · Aug 20, 2023

davesparks said:
I can't see a need for any wander lead or temporary connection for IR testing, what do you think needs a temporary connection?

All of your conductors should already be connected by the time you do the testing.

Hi, Sorry for late reply.

To my understanding of the GN3 Amendment 2 it states it here during install and then after install.
1st test: 500V IR test with the protective conductor connected to the earthing arrangement.
2nd Test: 250V with everything in place (except sensitive equipment obviously)

freddo · Nov 5, 2023

I think that's the rough idea, though the sensitive equipment IS connected for the second test, and no insulation test is carried out L-N for that test. That's how we do it anyway. If the equipment can't take 250V between live conductors and earth, it shouldn't be connected to the supply at all.

I like how that tester switch is labelled 'insolation'...

Edit, I've just see this is another old thread...