insulation resistance of a 3ph circuit in 2391

[bluesky]

Hi guys, another silly question, how to measure the insulation resistance in a 3phase circuite? shall i do it in 2 steps?

1: between cu and isolator/starter.
2:between isolator/starter and 3ph socket

cheers

 

[brucegenerator]

Turn off power.Simple installations should be checked as a whole.test to earth from all live conductors including neutral connected together.or each live seperatly to earth.when you have vulnerable circuits i.e.. dimmers etc.i think.

 

[Sintra]

Also have to test between phases.

 

[bluesky]

hi, i am still bit in dark, when i test continuity of a 3 phase circuit i should test seperately between cu and isolator; isolator and socket, then add up, but when testing insulation why should i test it as a whole?

please enlighten me!

 

[philbluespark]

is there any reason why you cant test between cdu and socket with isolator closed? (for continuity)

 

[WayneL]

Hi Bluesky,

You don't want to be doing it circuit by circuit - you'll be there 'til the following day

The procedure is simple.

Sub board main-switch open.

Motor isolator open.

Dimmer bypassed.

FCU bypassed.

All other switches closed.

Three phase board - all MCBs closed. Main switch open.

Select 500v range and perform ten point test.

i.e.

Place probe 1 on earth bar and probe 2 onto - L1.....L2.....L3.....N (4 tests)

Place probe 1 on neutral bar and probe 2 onto - L1.....L2.....L3 (3 Tests)

Test L1 - L2, L1 - L3, L2 - L3 (3 Tests)

NOTE: L1, L2 & L3 are tested on installation side of 3-phase main switch.

Then:

Test from motor isolator to motor (or 3 phase socket)

Test single-phase sub-board circuits individually (due to RCD) - should be two circuits - don't forget to throw the two-way switch to test your strappers.

Job Done

Don't think I've forgot anything.

PS
The 2391 board will be TN-S, if you had a TN-C-S supply you woulld have to remove the neutral test link otherwise you would get continuity between neutral and earth.

 

[bluesky]

thanks waynel, your answer is just like sunshine...

 

[gordon344]

Good answer, but what is the FCU?

 

[ian.settle1]

Good answer, but what is the FCU?

Fused Connection Unit is the correct terminology otherwords a fused spur

 

[Risteard]

The 2391 board will be TN-S, if you had a TN-C-S supply you woulld have to remove the neutral test link otherwise you would get continuity between neutral and earth.

You need to break the neutral link on any TN system - TN-S included - for the purposes of an insulation resistance test.

 

[WayneL]

You need to break the neutral link on any TN system - TN-S included - for the purposes of an insulation resistance test.

Hi Risteard,

I understand your reasoning, but I didn't on my 2391 and the assessor didn't say anything.

We weren't told to do it during the course, either.

Ironically, I got >299 M Ohms on my N-E test, but I do know why you're saying you should disconnect.

I can't understand why it didn't show up the fact that they are connected on the test. Any ideas?


It's alright, it's just come to me.

The 2391 board had a seperate 'main isolator' which was probably 4-pole.

When the assessor opened this, it will have disconnected the neutral as well

 

[Risteard]

The 2391 board had a seperate 'main isolator' which was probably 4-pole.

When the assessor opened this, it will have disconnected the neutral as well

You beat me to it. I suspect that is what has happened. When I did it we certainly had to break the link.

 

[Scotchydog]

im doing am2 on tncs do i have to remove the main neutral out of bar or take each one out and on my lighting circuit do i only flick the switches on whichever phase its on thanks

 

[Deleted member 26818]

im doing am2 on tncs do i have to remove the main neutral out of bar or take each one out and on my lighting circuit do i only flick the switches on whichever phase its on thanks

On single phase installations, the main switch will be double pole.
As such there is no requirement to disconnect the N-E link.

 

[i=p/u]

just link all phases together and test to neutral and earth , save bit a time,, ive just read something like this so not 100% ok i am 100% sure