Hot tub - TN-C-S

[snipersmith87]

Im after some advice regarding the earthing of a 32Amp hottub. I've yet to install one and am dubious about the risks associated.
The supply is T-N-C-S.
My plan is to put a seperate supply direct from origin via henleys to a 50amp MCB. 10mm 3c SWA approx 25m to a small wooden workshop. Within the workshop I'm locating a seperate DB with 30mA RCBO to supply small power / lighting within and the 32Amp hot tub sited on patio.
6mm 3c swa to rotary isolator. At this point I'm going to lose the supply armour via stuffing gland and internal cpc via wago. I was then going to install an earth rod connected to the load swa cpc and armouring upto hottub.
Can anybody see any issues with my scenario or further advice?

 

[suffolkspark]

I'm about to install a new supply for one on a job, after enquiring the hot tub manufacturer has said it does not require it's own earth electrode and is fine on tn-c-s...

Sparky mate of mine is installing one and the manufacturer for his one have said it must be on TT.

As much of a minefield as sodding car chargers

 

[Midwest]

I'm about to install a new supply for one on a job, after enquiring the hot tub manufacturer has said it does not require it's own earth electrode and is fine on tn-c-s...

Sparky mate of mine is installing one and the manufacturer for his one have said it must be on TT.

As much of a minefield as sodding car chargers

Never done myself, and I’m aware of the various issues, but isn’t one of the main concerns is what the bathers are stepping onto when they get out of the tub. That is grass or floor of wooden shed for example?

 

[Lister1987]

I've seen Matt:e units used to resolve earthing on TN-C-S arrangements, a few YouTubers using them;

View: https://youtu.be/l5DjBRiwCDc

View: https://youtu.be/usXBONOMAuQ

 

[suffolkspark]

I wonder if the tn-c-s safe ones simply have double insulated pumps? I'm going with manufacturer info on the one I'm doing, price is in now ?

 

[pc1966]

I suspect water heating is the risk, not the pump.

The Matt:e box is quite a reasonable approach but it relies on the volts being out of range and I did see a demo where you might not get enough L-N anomaly to detect a PME fault that has raised N+E to 70V or so above true Earth.

Still, nothing is ever perfect and it is about managing risk levels to a reasonable degree.

 

[suffolkspark]

True, every one I've done in the past I've staked, but this manufacturer saying it's ok has thrown me, I'll check it when it comes, they do final connections

 

[ChrisElectrical88]

I have done 3, always put a TT rod in for them. Would be interested to know why they say PME is ok with their product.

 

[davesparks]

I've seen Matt:e units used to resolve earthing on TN-C-S arrangements, a few YouTubers using them;

Of course the youtubers are using them, matt:e will be paying them to do it or giving them the units for free as its great marketing.

 

[snipersmith87]

I'm about to install a new supply for one on a job, after enquiring the hot tub manufacturer has said it does not require it's own earth electrode and is fine on tn-c-s...

Sparky mate of mine is installing one and the manufacturer for his one have said it must be on TT.

As much of a minefield as sodding car chargers

I went for the option of TT at the hot tub. Just sat better with me. I think you have to look at the external influences and siting of the tub. This was not near any other exposed conductive parts and located near retaining walls with soil etc. To me it should be treated as a swimming pool. If smashing a rod in will create a form of equipotential zone around the tub I'm doing it., albeit relying on a RCD for fault protection.

 

[Lister1987]

Of course the youtubers are using them, matt:e will be paying them to do it or giving them the units for free as its great marketing.

That is true but you would hope they have the professional integrity not to back rubbish.

 

[snipersmith87]

That is true but you would hope they have the professional integrity not to back rubbish.

I looked at these myself. I csn see them being very popular for EV chargers....but they're costly.

 

[suffolkspark]

Page 246 of regs book, reg 702.410.3.4.3 (ii) does say if using pme an earth mat or electrode with a resistance of under 20ohm linked to bonding is recommended..... so looks like full TT may be the right option afterall.

The problem I have with one of the tub jobs I've got coming up (different to the one I was on about a min ago) is the manufacturer has said the unit comes with just 3x 13A plugs attached, (one for heater, blower, and jets), top of page 248 says If I've got sockets they need to be atleast 1.25m from the edge of the tub, so that ones gonna require some thought let's see how long they come?

 

[davesparks]

That is true but you would hope they have the professional integrity not to back rubbish.

They likely don't know enough to know whether they are good or not. Whether they have professional integrity or not I doubt they have the knowledge to make that assessment.
The company making the product will certainly not have told them about any of the negatives, they will have blinded them with the marketing BS.

And you can't trust any review where tbe person doing the review is getting a bonus or reward for doing so, they will always be biased.

 

[Midwest]

And you can't trust any review where tbe person doing the review is getting a bonus or reward for doing so, they will always be biased.

Dave has a point there; they may not knowingly be biased, but they will find it difficult to be negative, to the hand that feeds them.

 

[pc1966]

Page 246 of regs book, reg 702.410.3.4.3 (ii) does say if using pme an earth mat or electrode with a resistance of under 20ohm linked to bonding is recommended..... so looks like full TT may be the right option afterall.

Having a good earth mat/rod near the pool like that might pull the PME fault down a bit, but it also pulls up the local "Earth" so folk are less likely to see a dangerous touch potential between them.

The problem I have with one of the tub jobs I've got coming up (different to the one I was on about a min ago) is the manufacturer has said the unit comes with just 3x 13A plugs attached, (one for heater, blower, and jets), top of page 248 says If I've got sockets they need to be atleast 1.25m from the edge of the tub, so that ones gonna require some thought let's see how long they come?

Time for a bit of joinery to put them inside an additional splash shield? You might be luck and find they come with enough flax, but I would like to see that first!