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Exposed 24VDC in a Bathroom

Harry Heathfield
Hello IET Forum,


I'm hoping someone can point me in the direction of a suitable standard that refers to exposed 24VDC conductors not being appropriate in a bathroom. My client would like to use the two metal hinges of a bathroom cabinet mirror as the +/- conductors; I'm not comfortable with them connecting any electricity through metal hinges, let alone in a bathroom! I've consulted with BS7671:2018; it says up to 30VDC is appropriate for the zone, but that doesn't mean exposed, of course! My client wants me to provide unquestionable evidence as to why they can't do it, but I'm struggling to find anything that isn't open to interpretation. Can anyone help?


The best I can find so far is from IEC 60364-4-41, Annex A.1 “Live parts shall be completely covered with insulation which can only be removed by destruction”.


Kind Regards, Harry
  • 0
    Hello Harry, you will get sensible responses on the I.E.T's B.S. 7671 Wiring & Regulations forum.


    Does the supply source comply with 414.3?


    701.414.4.5.


    416.1


    Section 414.


    Z.
  • 0
    This might do better in the electrical part of the forum but   here are some initial thoughts.

    The standard you quote is for LV installation  i.e.  50V to 1kV so not really applicable-  24V would be  ELV, and a bathroom cabinet sounds like an appliance, not an installation, for the same reason not really in the BS7671 domain either.

    It probably can be done in some way, but there are some considerations.

    I'd hope the current to be limited in a safe way, so there is no fire or damage risk if the user connects the hinges with something metallic, as this is a credible user action.

    How is the 24V derived - it needs to be SELV, so both 'floating' and isolated relative to the low voltage mains.

    How many watts are being supplied, and are the hinges the sort with a ball race ?  if so arcing and burning damage to the bearings may be an issue at high currents, though I'd expect an plain steel hinge to be OK to a few amps, brass rather more. If you wanted a kW I'd be very wary indeed.


    Mike.

    PS
    HSG85  as an example considers exposed conductors to be a hazard  at 50V and above, or if the available current is high, and then refers out to PD 6519 for the shock levels.

    Live parts that are uninsulated and exposed so that they can be touched either directly or indirectly by a conducting object are hazardous if the voltage exceeds 50 V ac or 120 V dc in dry conditions ; see BSI publication PD 6519 (3) ; and/or if the fault energy level is high; 

    The implication is that any exposed voltages a lot less than this, with current limit, are not really hazardous, in the eyes of the HSE. The key may be the dry conditions, in a bathroom folk may be wet and naked, less likely in a factory setting.
  • 0
    Have there been any reports of injuries or fatalities of, say, lorry drivers when changing a blown light bulb on a 24 Volt D.C. lorry lighting system in the rain?


    Z.
  • 0
    Hi Z and Mike,


    Thank you for your response. After doing more research and realising the previous standard I referred to isn't for ELV (thanks, Mike), I need to look at something a little more specific. I hope there will be a consumer type standard for products that will be applicable; I'm not too fond of the hinge being exposed, as a fault current or another unforeseen situation could lead to a dangerous outcome (potentially). I might need to speak to a specialist on the matter, but any further feedback would be appreciated.


    Kind Regards, Harry
  • 0
    Zoomup:

    Have there been any reports of injuries or fatalities of, say, lorry drivers when changing a blown light bulb on a 24 Volt D.C. lorry lighting system in the rain?


    Z.


    I have been told of of electrocutions on military vehicle electrics, which are more like 28V when in motion, but only in terrible circumstances, where the victim is already badly injured as to provide a low impedance subcutaneous contact, and to be honest death from blood loss was probably inevitable and  speeding it up may well have been a mercy.

    We have no compunction about having parts 28V apart exposed outside to touch at bumper height for jump starting and emergency power on big vehicles like the wolfhound or mastiff.  The centre hole in one of these will take a finger as a loose fit... I do not imagine either of these are situations that really apply to the original post.


    M.


  • 0
    24V is safe, especially SELV, the only safety issue I see in this application is dodgy connections causing heating.


    I would have no problem with bare 24V SELV conductors, you probably wouldn't want children sticking their tongues on them though, so a little common sense required, although they would only do it once!
  • 0
    Harry H:

    Hi Z and Mike,


    Thank you for your response. After doing more research and realising the previous standard I referred to isn't for ELV (thanks, Mike), I need to look at something a little more specific. I hope there will be a consumer type standard for products that will be applicable; I'm not too fond of the hinge being exposed, as a fault current or another unforeseen situation could lead to a dangerous outcome (potentially). I might need to speak to a specialist on the matter, but any further feedback would be appreciated.


    Kind Regards, Harry


    IEC 60364-4-41 does cover ELV as well as LV - including SELV and PELV.


    It's Chapter 41 of BS 7671 in the UK.


    However, the requirements for Bathrooms (Section 701 in the UK, IEC 60364-7-701 internationally) modify the requirements for SELV.


  • 0
    Rob Eagle:

    24V is safe, especially SELV, the only safety issue I see in this application is dodgy connections causing heating.


    I would have no problem with bare 24V SELV conductors, you probably wouldn't want children sticking their tongues on them though, so a little common sense required, although they would only do it once!


    That's not quite true. It depends on whether the ELV source limits the touch voltage in a fault to the maximum voltage in Section 701. Unfortunately, some sources are suitable for dry condition only, and some product standards permit a touch voltage of 120 V DC or 50 V AC in single fault conditions - which is classed as a risk in a bathroom.


  • 0
    No need to 'double post' the same question in the Wiring Regs category (it's something that's frowned upon and covered in our forum etiquette guidelines) if anyone sees a post that would be better suited in an alternative category, please feel free to @ mention one of the admin/moderator team (i.e. myself, Elizabeth Morgan or Evanna Gale) and we'll have it moved to the most appropriate category. ?


    This thread has now moved into Wiring and the regulations ?

  • 0
    Even if not actually prohibited I would consider it poor practice to have 24 volts DC fully exposed to touch in a wet location such as bathroom.

    I would consider that 24 volts DC should be at least somewhat enclosed or protected against touch, though not to the same standards expected for mains equipment.

    A non shuttered socket outlet for 24 volts DC, fine.

    A within reach lamp holder for 24 volts DC fine.


    A "tension wire" lighting system at 24 volts DC not good practice. Nor a similar voltage on exposed door hinges.


    I perceive some risk of poor contact, and the user fiddling with it with wet hands.


    The comparison with lights on lorries is relevant, only one pole of the supply is EASY to touch being connected to the body of the vehicle. The other ole of the supply is much less easy to touch being present on recessed lamp holder contacts and the like.

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