John asks this question, which concerns whether extra low voltage (ELV) and low voltage (LV ) supplies can be provided within the same cable. It has been answered by SELECT (Theme – Regulations and Legislation):
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Question: Can you advise whether it is acceptable to have different voltages within the same cable?
We normally run to 1.5mm ‘Arctic’ flexible cable to the luminaire; one feeds the light, the other the photocell, which is basically a control voltage monitoring the light levels.
The problem lies with the entry point gland to the lantern that only has capacity for one cable? Could I use a single five-core flex to supply both the lantern and the photocell?
Answer: Band 1 (ELV) and Band 11 (LV) circuits can be contained in the same cable where each conductor of a multicore cable is insulated to the highest voltage present, i.e. the Band 11 voltage.
Alternatively, this is allowed where the cores of the Band 1 circuit are separated by an earthed metal screen of equivalent current-carrying capacity to that of the largest core of the Band 11 circuit.
Refer to Regulation 528.1 - proximity to electrical services in BS 7671: 2008 (2015).
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