Insulation resistance testing

[Bradley6969]

Hi have AM2 next week and just need some help, 3 phase TP+N board, two way and intermediate lighting circuit with 3 switches obviously and one light, doing a global IR test, the lighting circuit say is on L1, so I’m testing all other circuits at once too do I have to switch my switches for every one of these tests
L1-L2,L1-L3,L2-L3,
L1-N,L2-N,L3-N,
L1-E,L2-E,L3-E, N-E

 

[westward10]

Doesn't really matter what position you have them in for the first test as long as you switch them all the other way for the second but yes you are correct.

 

[Bradley6969]

Or...

{L1+L2+L3+N} to E.
{L1+L2+L3} to N.
Then between phases.

I’m just on about when I need to switch my switches as lighting circuit is only on L1

 

[Bradley6969]

Doesn't really matter what position you have them in for the first test as long as you switch them all the other way for the second but yes you are correct.

Thanks for your help

 

[westward10]

Not sure about others views but I was always told when a switch is connected for two way operation it is never off or on, the lamp may be off but the switch still provides an output no matter its position.

 

[westward10]

I’m just on about when I need to switch my switches as lighting circuit is only on L1

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

 

[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.