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Testing of lighting circuits

Amos Owaga

I have been doing testing for low voltage installations and for the longest time I cringe whenever I start on the lighting circuits majorly for hotels where there is the lighting control systems because of the following challenges

1. CAT5/CAT6 cabling for control majorly for GRMS systems.

2. Circuitry where a single breaker serves 2/3 circuits looped from the main terminal of a switch to the next switch while only one cable seems to come from the breaker and makes the tracing of the circuits very difficult.

3. Borrowed neutrals and earths which gives very crazy results and sometimes the testing equipment is not able to give any analyzable readings.

How have you been able to do tests that conforms with the guidance of BS7671 and mostly is is required in the model form. and what are the possible tests to carry out in some of this circuits.

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    lighting circuits where control cables are involved as is common in hotel systems nowadays and how does one go about testing this kind of circuits.

    If the control cables are CAT5/6 then they're presumably SELV/PELV (or equivalent) so wouldn't need testing of themselves to prove safety from electric shock. You could do a basic insulation test to reveal potential functional problems (at 250V, looking for ≥0.5MΩ as per BS 7671) but in an exiting system where you'd expect to bridge all the live conductors together you could only test to Earth - so unless the cables are screened, it not likely to prove much at all.  In theory the equipment that sits between the cat5/6 cabling and mains (LV) should be insulation tested between the ELV and LV sides (according to the procedure for LV) - which could also prove separation of the ELV cabling from LV - but I'd be careful to check with the manufacturer's instructions before doing that. I suspect much of this (like central heating controls) often falls into the category of in theory should be thoroughly tested but in practice gets overlooked.

        - Andy.

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  • 0

    lighting circuits where control cables are involved as is common in hotel systems nowadays and how does one go about testing this kind of circuits.

    If the control cables are CAT5/6 then they're presumably SELV/PELV (or equivalent) so wouldn't need testing of themselves to prove safety from electric shock. You could do a basic insulation test to reveal potential functional problems (at 250V, looking for ≥0.5MΩ as per BS 7671) but in an exiting system where you'd expect to bridge all the live conductors together you could only test to Earth - so unless the cables are screened, it not likely to prove much at all.  In theory the equipment that sits between the cat5/6 cabling and mains (LV) should be insulation tested between the ELV and LV sides (according to the procedure for LV) - which could also prove separation of the ELV cabling from LV - but I'd be careful to check with the manufacturer's instructions before doing that. I suspect much of this (like central heating controls) often falls into the category of in theory should be thoroughly tested but in practice gets overlooked.

        - Andy.

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