Hot Tub Help!

[hoppy]

Been to look at a job.

Existing hot tub, been in for over year.

There are no manufacturers instructions, it is sited on concrete, about 25m from fuse board.

The customer is having problems as it is currently fed by what looks to be 1.5mm twin and earth, keeps tripping out when they turn the temp to certain point, also they can smell a fishy smell - the cable melting.

the hot tub came with a 230V industrial plug on it.

from what I can see from the panel inside the tub it requires a 32A supply.

The house is a tns no room on existing cu.

So, I am going to split tails, feed a new 2 way rcd unit, 32A mcb type c, 6mm 3 core swa to 32A rotary isolator.

With regards to earthing, I have read many posts on this but cant decide what is best.
Should I use the house tns earth on its own, or put a rod in also at the rotary isolator, or keep the hot tub separate and just tt the isolator.

I know some instructions ask for a rod, but I cant find them so I am asking what you more experienced guys would do for the best!

Thanks Guys!

 

[edexlab]

This Tub is direct on a patio which has dabs of mortar onto bare earth and a few inches below a mix of backfill rubble, this has made driving the rods in difficult and its several metres before the rod clears the rubble and is driven into earth

Having not seen the connection point in the tub I don't know if there is a terminal where a cpc to the board and conductor to a rod can be accomodated, so I've taken the rod conductor to the isolator 2 metres away

The possibility of an internal Rcd and an upstream one ?
I did ask the customer. before I started but he hasn't been able to tell me if there is or not

I was thinking discrimination isn't an issue here really, unless the Rcd within the tub is able to be tested, and if it is we agreed that I would temporarily link out or change the upstream Rcd for a main switch to enable testing of the downstream one
If it turns out there will be 2 Rcd's protecting, it would surely be preferable to having one which could fail ?

 

[Engineer54]

This Tub is direct on a patio which has dabs of mortar onto bare earth and a few inches below a mix of backfill rubble, this has made driving the rods in difficult and its several metres before the rod clears the rubble and is driven into earth

It could still well be conductive, especially when the area around the hot tub is wet from splashing water and people exiting the tub etc. Are the clients using chemical additives to the tub water such as bromine and PF correctors, which will in effect make the water more conductive??

So what sort of Ra values are you achieving with the earth rod install?? If it's particularly bad values, you may have to find a another location that is rubble free away from the patio, to drive your earth rod...

 

[edexlab]

Current reading is 45 ohms with 7 coupled rods down, close to the building wall,
I managed to get 2 in on the other side of the tub but I think there's probably 2m in rubble and whats left in clay? before a complete stop.
There are 2 locations where I can drive more into , 1 which is the closest is 5 m away. on the next level 3m down (as the property has several levels /stepped)
the other is 12 m away, again 2 m lower,
I was thinking that at these distances between rods, although it may lower the overall reading , will it actually have a positive effect or could it actually lead to a false sense of security,
I did think about using an earth electrode tester as I can borrow one, but with the location being on a patio partly on soil with building rubble and a few metres away is an underground room, so a layout of rods across the area was not practical , and I was thinking "mat" from the start but agreed to look at installing rods first to see how it went.

 

[Engineer54]

Wow, 7 Rods already and still only at 45 ohms!!!

What type of earth rods are you using here, not those 3/8 thin 1.2m twiggs i hope?? You seem to have a lot of rubble around this property, and to be honest you have positioned your earth rods in just about the worst place possible, next to walls where you will Always encounter old builders construction rubble/debris. You need to find a decent rubble free position, where you can couple 2 or even 3 X 5/8'' rods together to get a minimal depth of 2.4m. Perhaps it may be a good idea if you excavate say around 1m X 1m X 1m pit at the chosen position to get rid of any debris etc (will also confirm no services present that you may otherwise hit) You could also apply a conductive clay (Bentonite) or even a chemical enhancer in the excavated pit, though i'm not a lover of chemical enhancers, as they need reapplying on a regular basis as they dissipate into the surrounding ground....

 

[edexlab]

5/8 coupled 7 rods straight down by hand!
I know there will be limited contact here while the soil consolidates where the couplers have made the hole bigger
As for siting rods next to the building I know !
I lifted the slabs and tried different areas and managed an average of 16 inches , this one kept going , so did I lol

Although as I've said before there is a lot of rubble approx 2 - 3m and this one is now clear of that and presumably into clay ( house is on a riverbank)
Will having a rod further away be a problem?
I know it'll reduce the overall value but I'm thinking as the ground immediately around the tub is poor
I can definitely get some in on the side of the property which is around 14 metres away lovely soft ground!!

 

[Engineer54]

5/8 coupled 7 rods straight down by hand!
I know there will be limited contact here while the soil consolidates where the couplers have made the hole bigger
As for siting rods next to the building I know !
I lifted the slabs and tried different areas and managed an average of 16 inches , this one kept going , so did I lol

Although as I've said before there is a lot of rubble approx 2 - 3m and this one is now clear of that and presumably into clay ( house is on a riverbank)
Will having a rod further away be a problem?
I know it'll reduce the overall value but I'm thinking as the ground immediately around the tub is poor
I can definitely get some in on the side of the property which is around 14 metres away lovely soft ground!!

Are you saying you have 7 rods coupled together going down 8.4 metres?? If this is a riverside property, then you must of hit the water table at that sort of depth. I'm not sure if it's going to be a worthwhile exercise going for another position, if you only achieve 45 ohms going down 8.4 metres. Nothing to stop you trying mind, if money/costs is not going to be a problem. Maybe try excavating around the existing rod and treat with a generous amount of Bentonite....

 

[edexlab]

Yes 7 coupled together plus 2 in a nearby position, it is a riverbank
but I reckon the rods point will be just about the same level as the river now as the house is on a steep bank roughly 7/8 metres higher than the river bank edge

It was quite frustrating as I always keep putting rods in until I can't do anymore and aim for a highest reading of 20 ohms but if I can put more in I do and usually get it a lot lower, this has been for Domestic or Agricultural