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Hot tub lighting

AMC
Hi All
Ive been trawling the forums to try and make a judgement on which regs to follow.
Ive a client with a Wood fired Hot Tub, it has a blower and lights fitted. The manufacturer states the appliances is Class 2.
The hot tub has a internally mounted rccb 30ma, flex and European style plug which will be jointed to a swa cable under the tub.
Reading guidance from the Niceic and the IET I find a difference in opinion so I thought I’d ask you.
Niceic takes the view that Hot tubs are not covered under BS7671 so general wiring REG’s apply. However if fitted next to a swimming pool section 702 applies.
IET takes the view: “How could an electrical designer claim as a defence that the risks of electric shock for a hot tub installed outdoors is any less than that of a swimming pool, fountain or paddling pool, as defined in the scope of Section 702?”
So assume section 702 applies.

The hot tub has been placed on a slabbed patio area with two steps up to another patio area. There are ground mounted floor lights within 2 meters of the tub on the steps above the tub level.These floor lights are fed from a selv constant current driver with a max output voltage of 70V DC.

So if section 702 applies these lights would not be suitable looking at 702.55.4
So would you advise applying section 702 or general BS7671 regs?
My problem now is that each light is around £350ea and the ground works have been completed, so to change the lights/wiring would be very costly.
Also the earthing arrangement for the installation is TN-S. Which is ok for the class 2 hot tub?
Any advice appreciated.
Parents
  • 0

    I'm thinking of connecting the earth core of the SWA via a separate earth bar in the plant room to this steel work as an earth electrode. I could keep the armour connected to the TN-S system and isolate it via a plastic gland at the shed and use the TT connected 10mm core as the earth. The above reg doesn't specify where the electrode or earth mat is located.

    If I'm reading this right, the SWA would basically be on the TN system, but the 3rd core would be the earthing conductor for the TT'd shed? And the 3rd core would only be separated from the live conductors of the TN system by basic insulation.... so a fault (say impact damage to the buried SWA) could connect TN L to TT PE ... make the TT system live but not necessarily trigger ADS.

       - Andy.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    If I'm reading this right, the SWA would basically be on the TN system, but the 3rd core would be the earthing conductor for the TT'd shed? And the 3rd core would only be separated from the live conductors of the TN system by basic insulation.... so a fault (say impact damage to the buried SWA) could connect TN L to TT PE ... make the TT system live but not necessarily trigger ADS.

    That would be very unlucky for a shovel to impact the cable through the earthed (TN) armour into the phase conductor and (TT) earth conductor. without operating the protective device.

    So if I was to ditch the separating of the earthing systems and follow the recommendation on 411.4.2 regarding TN System 

    411.4.2

    It is recommended that an additional connection to Earth, by means of an earth electrode in accordance with Chapter 54, is made to the main earthing terminal. This recommendation does not apply to outbuildings of dwellings served by the installation.

    I could introduce the Structural steel work near the Main DB in the plant room as additional earth electrode.

    Id then satisfy this reg with using the TN-S earthing that's been provided?

    AMC said:

    702.410.3.4 Application of protective measures against electric shock

    NOTE: Where a PME earthing facility is used as the means of earthing for the electrical installation of a swimming pool or other basin, it is recommended that an earth mat or earth electrode of suitably low resistance, e.g. 20 ohms or less, be installed and connected to the supplementary protective equipotential bonding.

    Found this video interesting from efixx regarding 411.4.2 https://youtu.be/_owGBQia29U?si=WzwImtxOvKo8BtHU

  • 0 in reply to AMC

    Why not just TT the outbuilding with its own local rod? - you'd only have to achieve say 200Ω then, rather than 20Ω

      - Andy.

Reply Children
  • 0 in reply to AJJewsbury

    I have 24 swa cables and 6 KNX control cables out going from the shed, in every direction. I was very reluctant to drive a stake in, hence thinking of using a earth electrode at the feed end, (and over thinking the whole scenario).

    Any way problem solved, found a spare duct out of the shed to a clear location filled with decent fill with a sub 200 ohm reading.

    Supplier has changed the light fittings to 24V DC, but now has an extra 5 week lead time, the developer will be less than impressed with me.

    Out of interest, does anyone routinely connect earth electrodes to a PME system as per 411.4.2?

    Thanks everyone for your comments, very much appreciated.

    Cheers.

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