Electrician Jobs TT supply for hot tub

[gcwarr]

Hi,

I have recently had a hot tub fitted and am not comfortable with it being supplied directly from TN-C-S supply. I’m looking for someone to modify to TT, but struggling to find anyone locally who can help.

Location - Warrington, Cheshire.

Thanks.

 

[HappyHippyDad]

Hi,

I have recently had a hot tub fitted and am not comfortable with it being supplied directly from TN-C-S supply. I’m looking for someone to modify to TT, but struggling to find anyone locally who can help.

Location - Warrington, Cheshire.

Thanks.

Hi GC,
Could you explain your worries a little more?
It's unusual for a customer to even know what TNCS is, you clearly do and you are worried about it. Did you discuss it with the electrician before hand?
I haven't checked the most up to date regs on this, but did find the following from an (older) NICEIC article...

"Hot Tubs and TN-C-S Supplies The NICEIC Technical Helpline is often asked whether a hot tub installed outdoors may be supplied from a circuit taken from an installation forming part of a TN-C-S system, often referred to as a PME Supply. Neither the Electricity Safety, Quality and Continuity Regulations nor the guidance given in Engineering Recommendation G12/4 – Requirements for the Application of Protective Multiple Earthing to Low Voltage Networks published by the Energy Networks Association places any restrictions in respect of the connection of a hot tub to a PME supply. G12/4 does offer several alternatives in respect of the connection of a swimming pool to a PME supply and it is sometimes suggested, erroneously, that hot tubs should be treated in the same manner as a swimming pool. However, it is clear that hot tubs fall outside of the scope of Section 702 of BS 7671 (see Regulation 702.11). So, unless, as stated previously in this article, a hot tub outdoors is installed within the zones of a swimming pool, only the general rules of that standard are applicable."

 

[mainline]

Hi,

I have recently had a hot tub fitted and am not comfortable with it being supplied directly from TN-C-S supply. I’m looking for someone to modify to TT, but struggling to find anyone locally who can help.

Location - Warrington, Cheshire.

Thanks.

Section 702 applies to swimming pools, and the scope of the regs excludes hot tubs as they’re built to a product standard.

Although it is unlikely that a hot tub will have any metalwork present for a voltage to appear to true earth, the designer must bear in mind that a potential could be transmitted to the water through the earthing of the heating element. Adopting a TT system for the hot tub, greatly reduces this risk.

 

[gcwarr]

Hi GC,
Could you explain your worries a little more?
It's unusual for a customer to even know what TNCS is, you clearly do and you are worried about it. Did you discuss it with the electrician before hand?
I haven't checked the most up to date regs on this, but did find the following from an (older) NICEIC article...

"Hot Tubs and TN-C-S Supplies The NICEIC Technical Helpline is often asked whether a hot tub installed outdoors may be supplied from a circuit taken from an installation forming part of a TN-C-S system, often referred to as a PME Supply. Neither the Electricity Safety, Quality and Continuity Regulations nor the guidance given in Engineering Recommendation G12/4 – Requirements for the Application of Protective Multiple Earthing to Low Voltage Networks published by the Energy Networks Association places any restrictions in respect of the connection of a hot tub to a PME supply. G12/4 does offer several alternatives in respect of the connection of a swimming pool to a PME supply and it is sometimes suggested, erroneously, that hot tubs should be treated in the same manner as a swimming pool. However, it is clear that hot tubs fall outside of the scope of Section 702 of BS 7671 (see Regulation 702.11). So, unless, as stated previously in this article, a hot tub outdoors is installed within the zones of a swimming pool, only the general rules of that standard are applicable."

I work in functional safety, so the principle of As Low As Reasonably Practicable is in the forefront of my mind with regard to risk.

No there was no discussion with the electrician before the install, it was done as part of a package with landscape gardener. I know nothing is technically ‘wrong’ with the install.

With regard to concerns, mainline put it much better than I could have. I know that there are risks involved in a TT setup, but I think I would be more comfortable with this than risks with PME earth from supply.

Problem is finding a local electrician who will engage on this. Anyone I try loses interest as soon as a customer starts to talk technical!

Thanks for the replies so far, it’s good to at least be having a discussion about this.

 

[buzzlightyear]

I have a hot tub, and it is on PME.
But if needed it could be put on a TT.
But the chance of a fault on a PME system is about chance of getting a kiss from a garaff.

 

[mainline]

But the chance of a fault on a PME system is about chance of getting a kiss from a garaff.

 

[gcwarr]

Hi,

I have recently had a hot tub fitted and am not comfortable with it being supplied directly from TN-C-S supply. I’m looking for someone to modify to TT, but struggling to find anyone locally who can help.

Location - Warrington, Cheshire.

Thanks.

Appreciate the comments so far.

Anyone in the North West able to help, or at least advise on this?

Thanks.

 

[Tom256]

Appreciate the comments so far.

Anyone in the North West able to help, or at least advise on this?

Thanks.

I am not in your area so too far for me (North Yorkshire), as for advice without seeing the site any advice on-line would have to be rather generic. But I can see you want a discussion so will quickly start this off.

One of the issues (there are many to be considered) you have with hot tubs outdoors is the possible clash between manufacturers instructions and BS 7671 in particular BS 7671 411.3.1.1 which states:
(quote) 'Simultaneously accesible exposed-conductive parts shall be connected to the same earthing system...' (end quote)
Now this is not always as simple as it might suggest yet for want of any other information I offer it as the first question to be addressed. Hot Tub manufacturers may well state TT yet acceiving such in an area with TN-C-S is not that straight forward.
Yet it is possible and as this is what you the customer requires the design now needs to be looked at to see how this can be achieved. Now I am not saying it can be achieved for any one set of circumstances a site survey would be required and perhaps to assist somewhat photographs of the hot tub area, location from the main house and any out-buildings would assist
I have certainly heard of (some) Electricians unwilling to enter into discussion on matters of this form so what you say rings true. It is not for me to guess why for it seems a reasonable technical issue that a customer is faced with and skilled competent people can engage with. I wish you well with your search, there will be someone willing to come along, drink a coffee and discuss this through with you - Disclaimer: more cost may be incurred than just a spoonful of coffee at the survey stage.

I have carried out such works but it requires a good deal of 'spade work' before deciding to go ahead.
Any advice without being on-site must be taken as generic and may not be the best option for your circumstances. Some of the considerations however, for / against etc I am happy to bat around in a civil way

 

[gcwarr]

I am not in your area so too far for me (North Yorkshire), as for advice without seeing the site any advice on-line would have to be rather generic. But I can see you want a discussion so will quickly start this off.

One of the issues (there are many to be considered) you have with hot tubs outdoors is the possible clash between manufacturers instructions and BS 7671 in particular BS 7671 411.3.1.1 which states:
(quote) 'Simultaneously accesible exposed-conductive parts shall be connected to the same earthing system...' (end quote)
Now this is not always as simple as it might suggest yet for want of any other information I offer it as the first question to be addressed. Hot Tub manufacturers may well state TT yet acceiving such in an area with TN-C-S is not that straight forward.
Yet it is possible and as this is what you the customer requires the design now needs to be looked at to see how this can be achieved. Now I am not saying it can be achieved for any one set of circumstances a site survey would be required and perhaps to assist somewhat photographs of the hot tub area, location from the main house and any out-buildings would assist
I have certainly heard of (some) Electricians unwilling to enter into discussion on matters of this form so what you say rings true. It is not for me to guess why for it seems a reasonable technical issue that a customer is faced with and skilled competent people can engage with. I wish you well with your search, there will be someone willing to come along, drink a coffee and discuss this through with you - Disclaimer: more cost may be incurred than just a spoonful of coffee at the survey stage.

I have carried out such works but it requires a good deal of 'spade work' before deciding to go ahead.
Any advice without being on-site must be taken as generic and may not be the best option for your circumstances. Some of the considerations however, for / against etc I am happy to bat around in a civil way

Thanks for the response, makes perfect sense.

When I say advice, I mean if anyone is local to us and can advise in person. I understand any advice on the forum will be generic and this situation is dependent on many things about the specific site/setup.

 

[Tom256]

I am not in your area so too far for me (North Yorkshire), as for advice without seeing the site any advice on-line would have to be rather generic. But I can see you want a discussion so will quickly start this off.

One of the issues (there are many to be considered) you have with hot tubs outdoors is the possible clash between manufacturers instructions and BS 7671 in particular BS 7671 411.3.1.1 which states:
(quote) 'Simultaneously accesible exposed-conductive parts shall be connected to the same earthing system...' (end quote)
Now this is not always as simple as it might suggest yet for want of any other information I offer it as the first question to be addressed. Hot Tub manufacturers may well state TT yet acceiving such in an area with TN-C-S is not that straight forward.
Yet it is possible and as this is what you the customer requires the design now needs to be looked at to see how this can be achieved. Now I am not saying it can be achieved for any one set of circumstances a site survey would be required and perhaps to assist somewhat photographs of the hot tub area, location from the main house and any out-buildings would assist
I have certainly heard of (some) Electricians unwilling to enter into discussion on matters of this form so what you say rings true. It is not for me to guess why for it seems a reasonable technical issue that a customer is faced with and skilled competent people can engage with. I wish you well with your search, there will be someone willing to come along, drink a coffee and discuss this through with you - Disclaimer: more cost may be incurred than just a spoonful of coffee at the survey stage.

I have carried out such works but it requires a good deal of 'spade work' before deciding to go ahead.
Any advice without being on-site must be taken as generic and may not be the best option for your circumstances. Some of the considerations however, for / against etc I am happy to bat around in a civil way

Thanks for the response, makes perfect sense.

When I say advice, I mean if anyone is local to us and can advise in person. I understand any advice on the forum will be generic and this situation is dependent on many things about the specific site/setup.

Yes I can see you have a reasoned approach. All the best with the search.

 

[gcwarr]

Yes I can see you have a reasoned approach. All the best with the search.

Does it seem reasonable to have two RCD/RCBO inline to prevent single point of failure in a TT ‘island’ setup? Is it OK for both of these devices to be upstream of the TT island (i.e. at consumer unit on supply earth, then switch to TT earth at the hot tub end)?

Apologies if my wording is flawed or if this is a nonsense concept!

Thanks.

 

[buzzlightyear]

Does it seem reasonable to have two RCD/RCBO inline to prevent single point of failure in a TT ‘island’ setup? Is it OK for both of these devices to be upstream of the TT island (i.e. at consumer unit on supply earth, then switch to TT earth at the hot tub end)?

only one should be put in ,two in series is no good .

 

[mainline]

only one should be put in ,two in series is no good .

Unless it's time delayed

 

[Tom256]

Does it seem reasonable to have two RCD/RCBO inline to prevent single point of failure in a TT ‘island’ setup? Is it OK for both of these devices to be upstream of the TT island (i.e. at consumer unit on supply earth, then switch to TT earth at the hot tub end)?

Apologies if my wording is flawed or if this is a nonsense concept!

Thanks.

The concept is good yet - disclaimer - design would still be required to implement such.

I prefer when working with TT earthing and RCD's / RCBO's to use a multi-tiered approach as you suggest. It should be such that it can cascade protection with selectivity and still avoid the tripping of healthy circuits. Ensure double pole disconnection for all 'live' conductors throughout and you have 'pencilled' out an approach.

To TT at the Hot Tub end, yes, I have done so myself and is often easier. Just ensure you have complete isolation between the two earthing systems at this point of separation (perhaps at the isolator) and any other sources. 'Insulation' tape is not considered a suitable insulation - despite the name it adopts.

 

[Tom256]

Just noticed the comment on both devices being aside the consumer unit. Is the concept suggested here to place two x 30mA DP RCBO's in series side by side?
In a format of sorts you see such an arrangment required - yet not side by side - on caravan parks. With a 30mA RCD in the static caravan and a further 30mA RCD within the external supply point that the caravan is plugged into. As a result in the event of an earth fault either or both will trip.

Yet it is not the conventional way that layering of protection is provided it would be a single 30mA RCD / RCBO that would be used. Two 30mA RCBO's side by side in series, that is not to say it cannot be done, the regulations are not binding in such a way as to remove all design considerations. Both would/either/or trip and if side by side such may not prove any inconvenience to reset.

RCD's can be used for fault protection or for additional protection and they are selected accordingly. WIth fault protection the resistance of the TT earthing system sets what device can be selected.

 

[gcwarr]

Thanks for the advice so far. I now have a local qualified electrician engaged with this and an installation plan for TT earth at the hot tub and suitable cascaded RCD protection with selectivity at the supply end.

To TT at the Hot Tub end, yes, I have done so myself and is often easier. Just ensure you have complete isolation between the two earthing systems at this point of separation (perhaps at the isolator) and any other sources. 'Insulation' tape is not considered a suitable insulation - despite the name it adopts.

Out of interest, how would you usually achieve complete isolation of the two earthing systems at the isolator? In this case would the only incoming earth from the supply be via the armour of the SWA?