Hot tub installation !

[devonsparky]

This is a follow up to a thread I started yesterday.

I have been working all day installing a hot tub situated outside on a patio slabbed deck.

Contrary to what I was told, it was TN-C-S supply so here is how I have wired it.

• From Henly blocks - 25mm tails to a one way board (Main Sw RCCB - 50A MCB)

• 10mm 3 core SWA from board to 63A rotary isolator and from rotary isolator to hot tub

• Earth rod with 10mm G/Y back to one way board and then used one core as an earth to the hot tub and connected the armour to the earth bar too.

Time beat me today so I have not connected into the Henly blocks yet and tested .......................... Is this how you guys would have done it. 10 years in the game and an approved electrician and it's still nice to get feedback off of this forum !! ha ha

 

[baazab]

Who's Buff ?
;-)
rcd can be at the mains or local to hot hub if using swa , either is ok.
yes , connect swa and earth conductor together at the CU.

is it better at mains so then swa protctect by the rcd?

 

[SPARTYKUS]

There are specific circumstances where you cannot use Tncs (like caravan parks I believe, it has to be rodded, as a fellow forum member I know who works alot for the Caravan Club will testify).


Is a hot tub one of these instances?

The only other problem is with services like water pipes - which means main bonds also need to be extended- which could be a pain.


Apart from that I 'd rather have a Zs of 0.3 than 37 or 17 or 7 .....?

 

[Guest55]

Unless there's a specific reason, why can't you export it?

The Dno's dont approve of extending their PME earth beyond the equipotential zone of the building in which the supply is located.
This is only an issue if there is exposed / extraneous metalwork at or around the hot tub ,
as in the unlikely event of a neutral break this metalwork may rise to a dangerous potential.
hope this helps.

 

[keniff]

I replied in the other thread, I installed my tub using the supplied tncs earthing arrangement also putting a rod in at the tub end. This rod was well below 22 ohms as stated in the regs, the only problem I had was when you got out the tub and one leg was on the floor and one in the water you could feel a shocking feeling, slight difference between true earth and suppliers earth, therefor I disconnected the suppliers earthing and made the tub tt. Alls fine now so that's how I install them from now on!

 

[electric will]

Sparky, that's also my thought, I'm tempted to export now to be honest.

 

[electric will]

That's a point I mentioned that before, potential difference in the earth ( and tub full of water)

 

[Guest55]

There are specific circumstances where you cannot use Tncs (like caravan parks I believe, it has to be rodded, as a fellow forum member I know who works alot for the Caravan Club will testify).


Is a hot tub one of these instances?

The only other problem is with services like water pipes - which means main bonds also need to be extended- which could be a pain.
agreed , so in that instance you have a choice of running a 10mm earth bond from the MET to the outside pipes or , bang in earth rod near hot tub.
most choose the earth rod method if its a long run back inside and they're only using a 6mm cable anyway.


Apart from that I 'd rather have a Zs of 0.3 than 37 or 17 or 7 .....?
so would i lol

.......................

 

[electric will]

But if you export and have rcd protection how can people feel the tingle when getting in and out. This must be potential difference with the value at the met(via tncs) and the ground where the tub is located, part of body in the water and foot on the ground. Surely the max difference would be 50v any more the rcd would trip

 

[keniff]

Well I put my tester in the water and in the ground and was getting 2 volts. Not alot but you could really feel it

 

[devonsparky]

cheers for that 'keithsims' ................... NO exposed metalwork etc at the hot tub but I think if you TT it and the readings are good then this is the way to go.

 

[electric will]

I'm sticking with tt then, trouble is there's pros and cons for either.

 

[devonsparky]

Me too 'Will' ............. and I'm going to smash up my laptop so I can't read any more messages to alter my thinking anymore !!!!

 

[SPARTYKUS]

Rcd is statistically more (much more) likely to fail than loosing the PEN.

Now I am being devils advocate!

 

[electric will]

Maybe the you should have a 100ma at main board and a 30ma at the tub Why not just drag the hot tub into the lounge?

 

[mayfair]

Your some bloody comfort

Rcd is statistically more (much more) likely to fail than loosing the PEN.

Now I am being devils advocate!

 

[Engineer54]

last hot tub i did was off TNS , didnt bother with any rods :-D

If the hot tub was located on bare ground or grass, i think i'd be also installing a rod, even if it was a TN-S supplied installation. Your still going to get a potential difference between true earth and the DNO TN-S earth.....

As for the Regs, i think they state somewhere, that a TNC-S supply can be used, for supplying hot-tubs and the like provided an earth electrode of a certain value is also provided.... I think that value was around 20 ohms, but i wouldn't swear to it...

 

[electric will]

Oh don't start this thread again! I've made up my mind with these tt all the way

 

[SPARTYKUS]

How many lost neutrals have you seen? And how long before fixed.

Me-none.

Knackered RCDs owner unaware of, prob been like it since installation by a (*cough*) electrician?

Me-about 15.

 

[Engineer54]

Oh don't start this thread again! I've made up my mind with these tt all the way

I'd probably agree with you too, especially if the Tub was located/positioned on bare ground or grass, but not with anywhere near a 200 ohm Ra value... lol!!

 

[SPARTYKUS]

I think earlier posters were trying to decide on TNCS or TT. E54 you're proposing TNCS with a back up rod as well aren't you. All connected together, so to speak.