IR test with transformers and dimmer on circuit

[DaveS]

Evening Chaps

On a job at moment and testing lighting circuits that have a lot of down lighters and a dimmer. Am I correct that if I disconnect live neutral and cpc from board join L-N together with all switches in closed position and test this to cpc and do IR test I have pretty much proved no short circuit between conductors including my switch lines. I will be testing initially at 250v as not to cause damage to dimmer and transformers. Thanks

 

[J.C.E]

yes and any 2way switches- to be opened/closed and tested

 

[westward10]

Yes and test at 500v as prescribed.

 

[Richard Burns]

It is generally recommended to leave the cpc in the earth bar to ensure that other earthed conductors are not affecting the circuit.

 

[Ian1981]

As suggested in previous post the cpc needs to be connected to the means of earthing during an insulation resistance test, so don't disconnect from earthing terminal.
See guidance note 3.

 

[Ian1981]

Testing at 250 is only acceptable if electronic equipment cannot be reasonably disconnected but I would say in your case a dimmer is easily delt with and 500v can be used.

 

[westward10]

Testing at 250 is only acceptable if electronic equipment cannot be reasonably disconnected but I would say in your case a dimmer is easily delt with and 500v can be used.

The only time I use 250v is when filtered extension leads give false readings and I can't be bothered to unplug them otherwise, 500v all the time and thirty odd years on to my knowledge I have caused no damage.

 

[DaveS]

Thanks all very much appreciated especially advice on leaving cpc in earth bar had never considered other cpc's could affect circuit. Always learning

 

[Ian1981]

The only time I use 250v is when filtered extension leads give false readings and I can't be bothered to unplug them otherwise, 500v all the time and thirty odd years on to my knowledge I have caused no damage.

An Older bloke I worked with used to damage smoke detectors all the time on a 500v test line -neutral.
Must have damaged about 5 houses worth till he realised

 

[westward10]

Older bloke I used to work with used to damage smoke detectors all the time on a 500v test line -neutral.
Must have damaged about 5 houses worth till he realised

Rarely test L/N on periodics unless 100% sure there is nothing across it so that will only be socket circuits

 

[DaveS]

Is 500v not likely to damage transformers of down lighters? Also in this scenario for some silly reason all properties have been fed to switches so have atleast 5 neutrals and cpc's at back of box. I am trying to avoid as much any taking off and putting back of switch faces (which would have to do to bypass dimmer) incase I unintentionally cause conductors to become loose. This seems to be the sanest method so far

 

[Ian1981]

Rarely test L/N on periodics unless 100% sure there is nothing across it so that will only be socket circuits

Yeah we normally have an agreed limitation with clients in office eicr type premises.
No live - neutral IR testing on lighting circuits especially

 

[westward10]

Is 500v not likely to damage transformers of down lighters? Also in this scenario for some silly reason all properties have been fed to switches so have atleast 5 neutrals and cpc's at back of box. I am trying to avoid as much any taking off and putting back of switch faces (which would have to do to bypass dimmer) incase I unintentionally cause conductors to become loose. This seems to be the sanest method so far

Won't cause any damage what so ever.

 

[Ian1981]

I

Is 500v not likely to damage transformers of down lighters? Also in this scenario for some silly reason all properties have been fed to switches so have atleast 5 neutrals and cpc's at back of box. I am trying to avoid as much any taking off and putting back of switch faces (which would have to do to bypass dimmer) incase I unintentionally cause conductors to become loose. This seems to be the sanest method so far

its becoming common to take a mains down to switches with a neutral as it does away with needing unnecessary junction boxes above ceilings for things like downlights , makes it easier to terminate as well

 

[DaveS]

Very true about logic of sometimes wiring to switches but here I really can't see what they was thinking it's a wooden plinth box cut into and can only get depth of shallow back box really with size of dimmer really is hard work getting all conductors at back of box