Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, about insulation resistance (IR) testing on a domestic lighting circuit, is answered by SELECT:
Answer: The procedure is that you should de-lamp where appropriate and disconnect any transformers to enable a L-L IR test to be carried out in addition to the L-E IR test.
Normally on a new installation, you would carry out the IR testing before lamping up or connection of transformers, chokes, etc. If you are carrying out a periodic inspection, it may be appropriate to list in the 'limitations' section of the report that L-N IR tests were not carried out on lighting circuits', as to de-lamp or disconnect may be too time consuming.
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