Graham Church asks about the proximity of different wiring systems within ductwork. His question has been answered by SELECT (Theme – Cables, Wiring & Wiring Accessories):
Question: A customer of mine has gone to a great deal of effort to install underground ducting for a new project at his home. I know he is going to ask me to run a new power circuit (32A) out to his garden for electric gates and other uses, using this ductwork.
However, there are a number of low voltage (LV) cables already in-situ, namely data network, telecoms and alarm feeds. As I read it, according to Regulation 528.1, I must either make sure that all cables are insulated to the highest voltage present, or provide physical separation.
My feeling is that this installation will not comply with BS 7671:2011 if I run the new supply in this ductwork using SWA cable. Can you shed some further light on this please?
Answer: The Wiring Regulations (17th Edition) require that voltage Band I (ELV) and Band II (LV) circuits shall not be contained in the same wiring system, unless:
- Every cable or conductor is insulated for the highest voltage present.
- Each conductor of a multicore cable is insulated for the highest voltage present in the cable.
- The cables are insulated for the system voltage and installed in a separate compartment of the cable ducting or cable trunking system.
- The cables are installed on a cable tray system where physical separation is provided by a partition
- A separate conduit, trunking or ducting system is used.
- For a multicore cable, the cores of the Band 1 circuit are separated from the cores of the Band 11 circuit by an earthed metal screen of equivalent current -carrying capacity to that of the largest core of a Band 11 circuit.
Using SWA would meet the requirements in 6 above, so would be acceptable.
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