Hot tub circuit with earth rod

[Chapster]

I've never installed an earth rod so I'm looking for some suggestions.

I've been asked to wire up a hot tub. I was going to go from the DB with 3-core SWA to a rotary isolator on the house wall, then same SWA from the isolator to the tub.

Current system is a TN-C-S supply with a dual RCD board. So I want to isolate the PME cpc/armour at the rotary isolator and have TT from that point on.

How would you connect the rod's earth cable to the SWA armour and cpc from isolator to tub? I'm unsure if ring crimps on rod earth and cpc to the SWA banjo is good enough?

Would it be best to have an enclosure on the house wall with an isolator and earth terminal inside it, rather than try to do everything inside the isolator housing?

Recommendation for conduit to go underground from rod inspection box to isolator/enclosure appreciated too.

Thanks.

 

[ericmark]

It is not so much earthing, as bonding. The idea is, anything which you can touch from within the tub, or as you enter or leave, will be at the same potential to the water.

And should this not be the case, some device will remove the danger.

So step one, is to work out what is in the ground? If you sink an electrode close to a gas, water, or electric cable, under fault conditions, it could do the reverse to what you want.

I was given a figure of 8Ω for each earth electrode, and at 1.2 meters each, it varied from 3 to 8 rods, and this all at the same site (Point of Aye gas terminal) back to BS7671:2008 we see massive earthing systems for cattle sheds.

Domestic wise, we look at can you have a TT system with enough distance from the TN system to be safe. OK I can get 4 cars in my back garden, so yes I can likely get the distance my house to an outdoor bathroom, but I still have properties to either side and bottom, so really looking at around 2 meters from my borders and my house, yes I could do that in this house, but not in the last house.