Hot-tub install.

Discussion in 'Electricians' Talk' started by seneca2, Oct 14, 2010.

  1. seneca2

    seneca2 New Member

    Hi all, any comments on this one?
    The house is overhead supply, TT but had no earth rod or rcd, only earth being supplied by bonding to water and gas supplies. Consumer unit does have mcb's, as said no rcd though.
    Although not ideal, I fitted a front-end 30 m/a rcd and an earth rod a few weeks ago, purposely leaving it for a while to ensure no random tripping problems before connecting the additional circuit to feed the hot-tub. So now my plan is to use a spare 32a breaker in the consumer unit to supply the 10mm swa feed to the cabin where the tub is, effectively exporting the TT earthing to the hot-tub. The Ra I got at the rod was around 50 ohms, I think I might sink another rod at the far end as well though. I know none of this is ideal but they didn't want the expense of having the c/unit replaced, I did consider putting a seperate garage type c/unit with rcd at the house end just to supply the hot-tub but I didn't feel I could leave the house un-protected and of course I couldn't put the house on my earth rod without an rcd! I couldn't mount an rcd at the tub end due to lack of space in the cabin, not enough room to get it outside the zones, I have fitted an IP68 DP lockable isolator outside the cabin though. I suppose the basic question is, is there any reason not to export TT?
    Appologies for such a long thread but any comments much appreciated,
  2. FireballXL5

    FireballXL5 New Member

    I would be happy with what you've done.

    I'd probably take just a L & N and rod at the tub end.
  3. Caddy

    Caddy Active Member

    Could you elaborate as to why you think you are "exporting TT earthing
  4. larnacaman

    larnacaman New Member


    I know none of this is ideal but they didn't want the expense of having the c/unit replaced

    Great, got enough money for a hot tub, but not enough to keep them safe while using it!!! Typical British reasoning that!!!....
  5. Caddy

    Caddy Active Member

    Why why why oh why would you possibly take use L-N and rod the hot tub ?
  6. seneca2

    seneca2 New Member

    Could you elaborate as to why you think you are "exporting TT earthing"
    Hi Caddy, thanks for your interest, I know that 'exporting TT earth' isnt a term we usually use, it's just that for various reasons i'm not able to put an rcd at the tub end of the swa, so the main earth will be the rod at the house end (where the rcd is)therefore i'm likening it to situations where we export a tns/tncs earth. As I said though I will put an additional rod at the tub end hopefully eo equalise the earth potential.
  7. Coloumb

    Coloumb Screwfix Select

    If the cabin contains extrainious parts then your gonna have problems. I understand in a TT you can't export if this is the case and you will need a seperate TT earthing arrangement for the shed/cabin along with it's own RCD. I would say if there is a water supply then there are prooly gonna be ext. parts.

    stand to be corrected.
  8. Caddy

    Caddy Active Member

    So are you goingt to use the earth in the armoured from the house to the hot tub then connect that earth to a rod at hot tub location ?

    If so then you will need to make sure that the earth in the armoured is of a suitable size to be used as a CPC and Main bonding conductor.

    Why does correctly installing a circuit fully protected by an RCD as you are doing give you any reason to think you are doing something wrong or that you need to install a seperate rod at the other end?

    The only time you ever need to install a rod when dealing with out buildings is if as Coloumb has said there are etraneous-conductive-parts. Even then you dont have to install a rod you can just run a main bonding conductor.
  9. Lectrician

    Lectrician Screwfix Select

    I hate the upfront RCD.

    Would have preffered to have seen a new 2 way CU fitted (please dont call them 'shower' or 'garage' units). Rod at the origin as usual. No rod at the tub end.

    You would then address the original installation seperately.
  10. seneca2

    seneca2 New Member

    I would say if there is a water supply then there are prooly gonna be ext. parts.
    No water supply Col and all wood cabin although the floor is concrete, that's why I was thinking of putting another rod at that end. It's a 10mm swa and i'll earth the armour at both ends, that should satisfy the earthing conductor size. I've done several hot tub's now(although none TT before) and it always surprises me that they spend all that money and then have to fill it with a hose!, still, it saves us having to worry about extraneous conductive parts I suppose.
    Thanks for replies everyone.
  11. sinewave

    sinewave Screwfix Select

    Would've fitted a Rod & Type S RCD as a main switch if they won't have the DB replaced and then split the tails using Henlies after the Type S and fitted a 2 way DB with 30mA RCD then out to the Hot Tub
  12. seneca2

    seneca2 New Member

    That was my first thought Sine but I wouldn't want to put both circuit's on the same rod and I didn't think it right to have the 2 rod's close together, which they would have been in this situation. They are very agreeable people and do understand that we might have to alter things if tripping becomes a problem, which I doubt as it's been ok for the past month or so, whether that changes when the tub is connected we will see!
    My main concern is safety of course,
  13. Lectrician

    Lectrician Screwfix Select

    One rod with two CU's is fine - I would have done what sine suggests 100%. The 100mA type S being an inforced negotiation!
  14. wally2

    wally2 New Member

    I don't see the reason for fitting a rod at the tub end really sen. Its not really any different from wiring a shed down the garden etc. You have put a stake & earthing lead in at the house end & this is now the main earth ie connected to an earth block. You have done what you could with the lack of earth in the house, not ideal but I think I would have pushed a new dual rcd c/u a bit harder. In your case I would have fitted a separate 2 way rcd c\u for the tub & used the same rod. Don't see a problem with that. If you got 50 ohm then its pretty good, you are using RCDs remember.
  15. seneca2

    seneca2 New Member

    I didn't put an additional rod at the tub end after all Wally, The Zs at the far end was only around 20 ohms so I was quite happy with that. I would have used a separate 2 way board with it's own rcd but I wasn't sure whether there would be any problems having 2 rcd's sharing the same rod, but thinking about it of course it wouldn't be any different to using a dual rcd board which i've done lot's of on TT supplies! Still, there was a spare 32a mcb in the c/unit so all worked out ok, albeit everything's on the one rcd.
  16. wally2

    wally2 New Member

    As you say sen, no different, could have a c/u filled with 10 RCBOs. Did you get an offer to join them in the hot tub I wonder.

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