Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning possibly poor quality phase conductor insulation, is answered by BASEC:
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| Why does insulation light a neon screwdriver? |
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Question: I'm UK electrician working in Thailand. On more than one occasion, I've come across installations where the insulation of the phase conductor is live - with enough voltage to illuminate a neon test screwdriver! Do you have an explanation for this phenomenon? I would be grateful to hear it.
Answer: Poor quality insulation can break down!
Cable insulation material should have a high resistance, and this is normally tested at 3kV during manufacture. Poor quality insulation can break down over time, or pinholes in the insulation can result in reduced insulation resistance values.
Some types of insulation may degrade in wet conditions. Also, in a high humidity country like Thailand, there could be the effect of condensation, which can conduct significant electricity. Some neon test probes might also be subject to induced voltage, so check that too.
Any cable with insulation that has broken down sufficiently to cause a hazardous voltage to appear on other components should clearly be replaced.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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