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Garden radial 4mm - various accessories

vantech

Hi,

I am planning a garden installation where there is already a 4mm SWA available outside. My plan would be as follows: 

4mm radial from DB between 3 double sockets and 3-4 FCUs for lighting/pond/heaters. The accessories can accept 2x 4mm cables. The circuit will be protected by a 25A SP RCBO 30mA Type A. The total distance of cable from start to finish circa 30 metres and will be buried in various locations and run surface elsewhere. 

Electrically I can’t see anything wrong, and I don’t see any benefit in using RCD sockets as there is an RCBO at the start of the circuit. 

One of the sockets may be used for one of these blow up hot tops, which come with in-line RCDs. The supply is TN-C-S so this will be exported. 

Am I missing anything? Would I be better off TT’ing the potential socket that’s going to be used for the portable hot tub? I’ve seen lots of mixed opinions on this subject, some export PME, others don’t.

Thanks. 

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  • 0
    vantech said:
    Would I be better off TT’ing the potential socket

    Perhaps not. Hot tub aside, the thing you have to ensure is that you can't touch exposed-conductive-parts of equipment connected to TT at the same time as exposed-conductive-parts (and really other metalwork connected to MET) of the PME.

    If you can, then the installation is not compliant with BS 7671 (Regulation 411.3.1.1, second para).

    With respect to the hot-tub, it may well be that the heater at least has exposed-conductive-parts in contact with the water, so there is possibly a PME risk (in an open-PEN event) too. Would have to be investigated.

    I know some manufacturers of inflatable pools with heaters and pumps recommend they are unplugged when the pool is being used by people. How that works with 'bubbles" in an inflatable hot tub, I don't know without looking at one.

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  • 0
    vantech said:
    Would I be better off TT’ing the potential socket

    Perhaps not. Hot tub aside, the thing you have to ensure is that you can't touch exposed-conductive-parts of equipment connected to TT at the same time as exposed-conductive-parts (and really other metalwork connected to MET) of the PME.

    If you can, then the installation is not compliant with BS 7671 (Regulation 411.3.1.1, second para).

    With respect to the hot-tub, it may well be that the heater at least has exposed-conductive-parts in contact with the water, so there is possibly a PME risk (in an open-PEN event) too. Would have to be investigated.

    I know some manufacturers of inflatable pools with heaters and pumps recommend they are unplugged when the pool is being used by people. How that works with 'bubbles" in an inflatable hot tub, I don't know without looking at one.

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  • 0 in reply to gkenyon

    Thanks. 

    If this socket is the last point on the circuit (or indeed, any outlet/electrical accessory) within reach of the tub, was placed in a TT island, with the accessories having built in RCD protection, would this suffice? 

    The only potential issue I would then see is selectivity between the supply RCBO and the RCDs built into the sockets and FCUs that are on the TT. 

    The TT Island would be at the end of the garden, probably 20 metres from the houses supplement earth stake. This supplementary stake is connect to the MET with the PME supply. 

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