Hot Tub help.

[Soulsurfer]

Hey all, friend of mine just getting a hot tub they would like fed and not done one before so wanted to check on any advice with them as it seems quite heavy on the load requiring a 25A & 16A feed
25A supplies jets & pumps etc.. & 16A for heating elements.

House is on a TN-C-S supply 100A. Only 11.5 metre run from CU to point of hot tub but not sure if I can maybe use a multi core swa at 6mm rather than a separate 6mm & 4mm swa's ? Also am concerned that there are issues with earthing arrangements etc. was going to install an Rcbo at source but would that be incorrect ? Also diversity is there any allowable ?

 

[Soulsurfer]

Excellent that's real good of you, now for my induction into TT :smile5: thanks for helping mate. I totally prefer over cautious than probably ok to be honest too.

 

[davesparks]

Soulsurfer, been reading this thread for a few days and as you say this area new to you and therefore you are doing the right thing in asking, and i think you are asking the right questions. Generally when i install hot tubs off a PME supply i do not use the pme earth for hot tub. I would take a supply L+N fused in distribution board to an insulated enclosure with a EN61008 dp rcd rated at 30mA. I would then dig a trench and install an earth tape as opposed to an earth rod, (Tape 3mm * 25mm * 25 metres generally). Then check earth loop impedance of tape, which you require to be as low as possible. Depending how close you are to PME grounding could be as low as 0.40 ohms or even as high as 200 0hms. When you are satisfied that earth loop impedance is satisfactory and will stay that way in all weather conditions etc, carry on with install using TT earth as opposed to PME earth. Label accordingly so that the two never become joined. Hope this helps.

You are testing earth electrodes incorrectly if the proximity of a DNO earth electrode is affecting the result to such an extent.

Why on earth are you not using the far better PME earth connection for hot tubs? There is no requirement to do this in the regulations, merely a recommendation to install an electrode connected to the main bonding of the installation.

 

[Buckfast]

Your very welcome. Best Regards Buckfast

 

[Midwest]

Why on earth are you not using the far better PME earth connection for hot tubs? There is no requirement to do this in the regulations, merely a recommendation to install an electrode connected to the main bonding of the installation.

Interesting subject, and as I previously stated no expert in this area, and I'm not currently installing a hot tub! The links I posted #8 (note the last one fails) have a discussion on TNC-S supplies to hot tubs. I think it is fair to say the consensus for TNC-S supplied hot tub - in worst case scenario, with tub outside, situated on the lawn for example - is to convert (at tub end isolator) to TT. I recognise that re 702.410.3.4.3 does not preclude the use of a pme earth & recommends adding an 'additional' earth rod to the pme means of earthing.
I've found a couple of pdf's etc on the issue; http://www.google.co.uk/url?sa=t&rc...pe=pdf&usg=AFQjCNGzR0CSqgATvs1_jcKK3XtD-CDM7g
Swimming pools: to bond or not to bond? - IET Electrical
http://www.google.co.uk/url?sa=t&rc...pe=pdf&usg=AFQjCNEkQbO5R9aWPLD16Phth0h2EuQzdg
These are split 2 - 1 in favour of 'recommending' converting to TT earthing.
Lastly, Soulsurfer has not actually described where the hot tub is being installed, perhaps you could advise us of that Soulsurfer?

 

[Soulsurfer]

Hi mate, Hot tub is apparently being installed on a custom laid concrete pad, Pool lads have told me that they are digging up lawn this week to pour the pad and then it will sit there which is about 0.8 to 1 metre off corner of house in back garden area. Small garden almost all grass with metre or so of patio slabs around the edges before the lawn starts.

 

[Midwest]

Hi mate, Hot tub is apparently being installed on a custom laid concrete pad, Pool lads have told me that they are digging up lawn this week to pour the pad and then it will sit there which is about 0.8 to 1 metre off corner of house in back garden area. Small garden almost all grass with metre or so of patio slabs around the edges before the lawn starts.

I think that would be consider as almost as 'bad as' being placed directly on ground earth (i.e. soil or lawn). You will need to ensure correct earthing - which ever way you intend to do it, as I said I'm no expert. Perhaps the other more informed members will post back later today. Your client perhaps consider using some composite/plastic decking around the hut tub to alleviate the issue (the correct earthing still needs thinking about). Seen this decking install around a jacuzzi on a hols recently, and it looked quite effective. Certainly better than stepping concrete or muddy lawn. The composite decking was laid around the tub after it had been installed.

Perhaps the earth tape (as suggested by Buckfast) could be laid in the slab before the concrete is poured?

 

[Buckfast]

Do not think putting earth tape in concrete is the best of ideas ?. I have already advised the best approach to doing install and the only real deliberation is earth rod's, earth tape or earth mat. No need to keep re inventing the wheel do it once do it right and guarantee its safe. Hot tub PME or TT, TT every time.

 

[Midwest]

Do not think putting earth tape in concrete is the best of ideas ?. I have already advised the best approach to doing install and the only real deliberation is earth rod's, earth tape or earth mat. No need to keep re inventing the wheel do it once do it right and guarantee its safe. Hot tub PME or TT, TT every time.

Ok perhaps not the best of ideas, just thinking of the earthing of reinforcing rods in swimming pools. I think you might be in for some debate on the PME & TT thing!

 

[Soulsurfer]

No worries I'll be doing whatever it takes to get a low reading while it's bone dry as talking to other sparks locally every single one of them has thrown onto an Rcd or Rcbo & left them supplied solely from & earthed to TNC-S. Maybe they're going to get some issues. I just want to do it perfect first time & sleep easy

 

[Midwest]

Couldn't agree more.

 

[davesparks]

Do not think putting earth tape in concrete is the best of ideas ?. I have already advised the best approach to doing install and the only real deliberation is earth rod's, earth tape or earth mat. No need to keep re inventing the wheel do it once do it right and guarantee its safe. Hot tub PME or TT, TT every time.

But a PME earth is a much better earthing connection than what is normally achievable in a domestic TT. The addition of a supplementary electrode connected to the MET is the only suggestion in the regulations on the matter.

And why do you say putting tape in the concrete would be a bad idea? It would be a bit pointless when you can connect directly to the reinforcing, but other than that it is a good idea considering the ground will already be dug out.
If you want to follow a design used in larger installations then a tape round the perimeter with connected rods at each corner of the slab could be done

 

[Buckfast]

I would have to agree that the earth value from a PME supply will be far better than a TT, subject on how much money you are prepared to throw at it. There are a lot of unknowns with this thread with regards to supply. Is supply cable overhead underground etc. There is a lot of argument regarding reliability of PME connection, OC neutral conductors etc with some saying they never go OC. I live out in the sticks with a great deal of over head and underground cabling and have seen a good number of PME earth faults with earthing conductors carrying enought current to blow plaster off walls and quite literally burn out. By installing TT i feel i can totally guarantee a good earth path together with rapid disconnection time and guaranteed safety. Some argue that a second 100mA T/delayed rcd should be used upfront as a belt and braces approach, but how far do you go. I would have to say i would never install hot tub on PME supply but always as a TT installation. Connecting earth rod/tape to PME MET is a no go area for the reasons above with me.

 

[Soulsurfer]

The supply is totally underground & transformer substation is 40 metres away from property. Other than that I think everything is covered & Thanks to all of you that have helped me

 

[Leesparkykent]

I'm with Buckfast with regards to making the hot tub TT, due to small differences in potential between the TNC-S earth and true earth.

 

[davesparks]

Bearing in mind there is the opportunity to get an earthed mesh in the concrete in this case I see no reason not to use the PME connection in this case .