Insulation resistance testing

[Bradley6969]

If you are doing a global reading the three phases should be linked together.

Yeah global, I’m just lost when to switch my switches

 

[westward10]

Test 1, connect the three phases and neutral together, test to earth.
Test 2, swap the switches to their other positions, test again to earth with the three phases and neutral still linked.
Tests 3 and 4 the same with the switches and test to neutral with just the three phases connected together.

 

[Bradley6969]

Test 1, connect the three phases and neutral together, test to earth.
Test 2, swap the switches to their other positions, test again to earth with the three phases and neutral still linked.
Tests 3 and 4 the same with the switches and test to neutral with just the three phases connected together.

That’s what I asked them at the test centre but they said not to link them just do it bit by bit

 

[Richard Burns]

I have prepared a diagrammatic representation of potential testing options that may help to clarify or may just confuse.

I have also attached an indication of when three way switching conductors are connected to the supply. Red cores are live, brown cores are not connected.

So long as you have covered all options then the method is not critical but you may be asked to perform the tests in a specific way in an exam, if this is the case then follow the method you have been taught.

 

[Bradley6969]

I have prepared a diagrammatic representation of potential testing options that may help to clarify or may just confuse.
View attachment 38828
I have also attached an indication of when three way switching conductors are connected to the supply. Red cores are live, brown cores are not connected.
View attachment 38829
So long as you have covered all options then the method is not critical but you may be asked to perform the tests in a specific way in an exam, if this is the case then follow the method you have been taught.

Cheers for detail helps a lot, I’ll just do L1-N,L1-E,L1-L2,L1-L3 can’t go wrong then

 

[Bradley6969]

I have prepared a diagrammatic representation of potential testing options that may help to clarify or may just confuse.
View attachment 38828
I have also attached an indication of when three way switching conductors are connected to the supply. Red cores are live, brown cores are not connected.
View attachment 38829
So long as you have covered all options then the method is not critical but you may be asked to perform the tests in a specific way in an exam, if this is the case then follow the method you have been taught.

So if I do L1-N,L1-E,L1-L3,L1-L2 and switch switches each time then that’s fine or is there not need to do L1-L2,L1-L3

 

[Richard Burns]

If you consider the wiring arrangements from CU to end of circuit, then if you have a single phase circuit leaving the CU to go to the lights so long as the wiring for the switches and light fitting for that circuit is not run in the same containment as other phases, as Lucien has said above, then the switch wires, strappers, etc., everything but the supply cable for that circuit, will not be involved with the other two phases and so if you start your IR testing at the DB then you will test L1 to L2, L1 to L3, L2 to L3, L2 to N, L2 to E, L3 to N, L3 to E and N to E and the light switch wiring is not relevant, then when you test L1 to N and also L1 to E, at that point you need to switch the switches and repeat the L1-N, L1-E tests because you need to ensure there is no cable damage within the strappers and switched line.
Composite quick diagram of cable separations on wiring from DB.

If you do test L1 to L2 and L1 to L3 then there should be no problem with doing this as you are be cautious in case some wiring may have crossed over at a distant point you are unaware of and so are safe. In the exam situation you will be able to easily see if the strappers and switched line are in mixed containment with L2 and L3.

 

[Bradley6969]

If you consider the wiring arrangements from CU to end of circuit, then if you have a single phase circuit leaving the CU to go to the lights so long as the wiring for the switches and light fitting for that circuit is not run in the same containment as other phases, as Lucien has said above, then the switch wires, strappers, etc., everything but the supply cable for that circuit, will not be involved with the other two phases and so if you start your IR testing at the DB then you will test L1 to L2, L1 to L3, L2 to L3, L2 to N, L2 to E, L3 to N, L3 to E and N to E and the light switch wiring is not relevant, then when you test L1 to N and also L1 to E, at that point you need to switch the switches and repeat the L1-N, L1-E tests because you need to ensure there is no cable damage within the strappers and switched line.
Composite quick diagram of cable separations on wiring from DB.
View attachment 38834
If you do test L1 to L2 and L1 to L3 then there should be no problem with doing this as you are be cautious in case some wiring may have crossed over at a distant point you are unaware of and so are safe. In the exam situation you will be able to easily see if the strappers and switched line are in mixed containment with L2 and L3.

Thanks I understand now the lights are only from one phase so L1-N and L1-E should be fine, does it matter how I switch my switches eg have them all on then test then all off and test again or not

 

[Richard Burns]

Thanks I understand now the lights are only from one phase so L1-N and L1-E should be fine, does it matter how I switch my switches eg have them all on then test then all off and test again or not

I think the recommendation for testing is that you test and then operate each switch once with testing in between, I have not actually worked out if that will cover everything but it probably will.

I have put this information in the First IR testing diagram.

Single phase, light switch installed on L1, so testing to L2 and L3 not required.
Testing between Neutral and earth not required as no change on switching line.
Test L1 to N and L1 to E only.
Testing must cover each cable core at each point.

3 wire switching will connect every core to supply when light switch is on.
So testing L to N and L to E and switching any one switch once and then testing L to E and L to N again will cover all cores whether the switch was off or on to start with.

2 wire switching must test each strapper, there is no need to switch the intermediate switch.
If you know which two way switch is the line supply then testing L to N and L to E and switching this switch and testing L to E and L to N again will cover all cores.

If you do not know which switch has the line supply then testing L to N and L to E then switching one two way switch and testing L to E and L to N again and then switching the other two way switch and testing L to E and L to N yet again will cover all cores.
Exam conditions may require more rigorous testing.

 

[Richard Burns]

If you follow the switching options on my indication of live conductors diagram then you can see which conductors become live and are therefore part of the IR test at the supply when you operate switches.
I have just looked through them and operating each switch once will cover all cores no matter the wiring method, so perhaps this should be the default approach, though it does mean a lot more tests than I would like to perform. Eight tests as opposed to four or six. However it would ensure accuracy.

 

[Bradley6969]

If you follow the switching options on my indication of live conductors diagram then you can see which conductors become live and are therefore part of the IR test at the supply when you operate switches.
I have just looked through them and operating each switch once will cover all cores no matter the wiring method, so perhaps this should be the default approach, though it does mean a lot more tests than I would like to perform. Eight tests as opposed to four or six. However it would ensure accuracy.

3 phase board, lighting circuit on single pole mcb let’s say L1, T+E to first switch 3 core to next switch and 3 core to last with T+E to ceiling rose on last switch, so I will only have to switch the lights when doing the global test on L1-E and L1-N as only T+E feeding switch

 

[Richard Burns]

Sounds like you are about there.
So you have this wiring arrangement

I would say this statement "so I will only have to switch the lights when doing the global test on L1-E and L1-N " is correct, however I am not quite sure why you have added "as only T&E feeding switch".
Possibly because the cables between the switches and to the light are not close to the other phases.

 

[Bradley6969]

Sounds like you are about there.
So you have this wiring arrangement
View attachment 38838
I would say this statement "so I will only have to switch the lights when doing the global test on L1-E and L1-N " is correct, however I am not quite sure why you have added "as only T&E feeding switch".
Possibly because the cables between the switches and to the light are not close to the other phases.

Yes what I meant was there’s only one phase to lights so will only need to switch when either L1-N or L1-E

 

[Richard Burns]

Correct.
(Not available from now on today)

 

[Risteard]

Yes what I meant was there’s only one phase to lights so will only need to switch when either L1-N or L1-E

And L1 to both L2 and L3.

 

[Bradley6969]

And L1 to both L2 and L3.

How come

 

[Gavin John Hyde]

so glad i'm getting outof it after 50 yeaqrs. back in the day, it was wire it, connect it....if it went bang, then tester came out.

For a lot of fly by night electricians it has not much changed.... they turn it on and if it goes bang they run off to the next job,

 

[Risteard]

How come

In case the insulation breakdown is between phases.

 

[Bradley6969]

In case the insulation breakdown is between phases.

Didn’t have to do that lights was on L1 so I flicked switches between L1-E L1-N and passed

 

[Risteard]

Didn’t have to do that lights was on L1 so I flicked switches between L1-E L1-N and passed

The lights might be on L1 but the insulation breakdown on the strappers that you are testing for could be to another phase.