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RCD for outdoor public Car Park high mast lighting

Gyaneshwar Kumar

Hi all,

Hope you're doing well.

I'm working on a project where we're installing a number of high mast floodlights and lighting columns (6m high) in a big public car park. I'm trying to determine whether these lighting circuits require RCD protection.

BS 7671 isn't entirely clear on this. It states that lighting accessible to the public requires RCD protection, but it also specifically excludes street lighting, so I'm not sure which category this installation falls under. Also, technically  there's the need to balance the use of RCD against the risk of nuisance tripping.

Have you come across a similar situation before, or do you know how this is typically approached?

Thanks for you help.

  • 0 in reply to gkenyon

    I don't follow

    What I was trying to get at was (if my reading between the lines of the reports is right) the fundamental problem was lack of earthing/ADS - and if that had been got right the poor boy almost certainly wouldn't have died in those circumstances, RCD or no RCD. By all accounts it wasn't that some fuse failed to blow, an MCB that failed to trip, or gradual deterioration of a c.p.c. but basic lack of good workmanship at installation time.

    For sure an extra layer of protection might have weighted the odds a bit more - but where do you draw the line? - open PEN detectors next? 

      - Andy.

  • 0 in reply to Alan B
    Alan B said:
    Which was put down to poor maintenance and not resolving a known problem, but presumably if there had been an rcd in place, even if it was 500mA it would probably have tripped and prevented the incident.

    Another interesting one ... which begs the question quite where and what was the fault and where would the RCD have been placed? 714.411.3.4 only seems to ask for 30mA RCD protection for the lighting itself - rather than the steel column that's holding it up. So, especially where the supply is looped from one column to the next, you might well expect see RCDs in the base of each column ... so if the fault is upstream of that point the RCD may or may not be of much help. 500mA ones may or may not trip before the victim makes contact - all depends on how much of the c.p.c. is left or if there's some other path to earth (steel columns in the ground might seem like they'd be their own electrode, but the roots are commonly painted with bitumen paint to reduce corrosion and/or planted in plastic sleeves to limit damage to structures during future replacement, so nothing is reliably guaranteed) - in the case of direct contact or similar when practically all the fault current goes through the victim a 500mA device is perhaps unlikely to trip at all as body resistance alone (often circa 1kΩ) will often limit the residual current to below 250mA - maybe less when footwear, ground coverings, dirt or paint layers are taken into account.

       - Andy.

  • 0 in reply to AJJewsbury

    Didn't think about the base of the columns being protected. That makes things more challenging without a good path to earth.

  • 0 in reply to Alan B
    Alan B said:
    Which was put down to poor maintenance and not resolving a known problem, but presumably if there had been an rcd in place, even if it was 500mA it would probably have tripped and prevented the incident

    Yes, I think that is the main issue ... RCDs can provide protection when other measures fail. Give or take 'Type F' or 'Type B', they are relatively inexpensive. This makes them quite generally, under Health & Safety legislation, "reasonably practicable" ... 

    Following on from that, Section  2 of H&S@W etc. Act puts a duty on anyone operating a business to take reasonable care for the health & safety of anyone in their employment, and Section 3 of H&S@W etc. Act puts a duty on anyone operating a business to take reasonable care for the health & safety of anyone not in their employment that might be affected by their undertaking.

    Bringing this all together, in general, it might be considered by a court of law that businesses ought to provide RCDs ... of course, dependent on the particular circumstances.

    This has a knock-on effect to electrical contractors and designers who are classified as 'designers' under CDM Regulations ...

  • 0 in reply to gkenyon

    What about using something like a 100mA Type S RCD (delayed RCD) in the high mast floodlights and lighting columns?

  • 0 in reply to Sergio Fernandez
    Sergio Fernandez said:
    What about using something like a 100mA Type S RCD (delayed RCD) in the high mast floodlights and lighting columns?

    The 100 mA RCD could be used for ADS, or for additional protection against fire.

    The point is, if there is no 'earth path' to operate the RCD, 100 mA can be fatal, but 30 mA might not be.

    In summary:

    • RCDs with residual current rating exceeding 30 mA are not recognised by BS 7671 as providing additional protection against electric shock (Regulation 415.1).
    • RCDs with residual current rating exceeding 300 mA are not recognised by BS 7671 as providing additional protection against fire (Regulation 532.2).

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