Hot Tub plan

[george02]

Hi people, stupidly bought a hot tub on a whim and would appreciate some advice.
Firstly I’m not an electrician, done quite a bit of domestic back in the day, but know my limitations and don’t intend to do any final tests or connections that’s for the pro`s, so please don’t bombard me with part P regs etc.
I`m happy to do all the donkey work, so just asking for a bit of advice on my plan of attack.
Hot tub has max rating 32a, is on a flag base about 23meter total from the house, and around 10 meter from the garage.
House is TNS; garage already has a 63a RCD mini cu fitted.
My plan is using 6mm swa running off a spare 32a MCB on the main cu.
Unit is plastic and a bit flimsy, so planning a metal junction box fitted next to the cu,
gland off the swa at this box and run the wires direct to the MCB, with a return earth to the gland.
Can`t sink the armour as path is set flagstone so going conduit, saddled to the wall for 13m to the CU in the garage, then sink the last 10 m of cable to hot tub.
Does that sound reasonable?
Would I need to fit a rotary isolator as well? Just thinking more connections, more drop etc, and as it would be inside the garage feet from the cu it seems overkill to me, but do the regs demand?
Also would there be any benefit/drawback to dropping a rod at the tub end and extending the existing earth wire, from the tub terminal through to that as well? Or is that going o-TT ('')

Any help or suggestions would be greatly appreciated

 

[ban-all-sheds]

please don’t bombard me with part P regs etc.

Hopefully you won't regard this as "bombarding":

You cannot (legally) ignore Part P - everything you or anyone else does must comply with it.

Any help or suggestions would be greatly appreciated

You need to decide what you are going to do about the requirement for Building Regulations approval for this - nobody here can give you any advice on that apart from "this work is notifiable, so it must be notified).

You can either have the whole lot done by a registered electrician who can self-certify after the event, or you can apply for Building Regulations approval in advance and agree with them a plan for who will do which bits of the design, the construction, the I&T etc, and what kind of electrical certificate they will want to see, and from whom.

Or you can try and find an electrician who is happy for you to do some of the work and still go ahead and tell the authorities that she did it all. In which case you must find that person first, and agree with her what you can do under her supervision and direction, and allow her to make whatever design decisions she feels are appropriate.

 

[Taylortwocities]

There are a lot of questions to ask. You rally need an electrician to design this.

Basic stuff then
Do I guess that your plan would be to power the hot tub from the mini CU in the garage? How does that CU get its power? Is the source and cabling even able to deliver 32amps to the hot tub?

 

[george02]

I know the work is notifiable etc, I was not questioning that. just wanted to know in principle if what i had in mind was something like good enough to present as a plan? Or am i completely away with the fairy's with my understanding of electrical services?
I know its up to them to decide if it`s workable, or if they will allow me to do the donkey work etc.
I`m not a skinflint but don`t want to be paying a tradesman to run conduit and cable, dig trenches and fasten some boxes to walls.
I also understand the electricity and water do not make good bed fellows and I certainly do not intend to put me or anyone else in any danger.
But by the same account I don`t want to be standing there like a nodding Churchill dog while the local Dick Turpin sucks through his teeth and tells me its gonna be a trizillion pounds because I will need a special comptractification device because I live in an area of high density mensondroginites!
Just a simple, yes that may work but discuss it in detail with your electrician, or no you complete fool you will destroy the earth if you even contemplate such electrical heresy would suffice.

 

[Taylortwocities]

George, there is a lot to consider with this sort of project. More than you will appreciate (hence my first post above).

With respect, you do not have the skills to do this yourself, and you recognise that.

Your best way forward is to find an electrician you can work with. He can survey what you have and decide with you a plan for the job. No electrician likes crawling around in gardens, digging trenches and running armoured cable in Februaury. He/she will probably be delighted that you are prepared to do the grunt and reduce his/her labour, and your cost. He/she would then be able to do the tricky bits to turn it into a successful hot tub - as well as carry out the legal paperwork for the installation.

If you do not know an electrician then you can find a list of the registered ones at http://www.electricalcompetentperson.co.uk
remember that being registered does not reflect the ability of an electrician. It soften best to get a recommendation.

 

[333rocky333]

Im not a lover of swa surface clipped, so like you I sometimes threadle it through conduit and couplers as I find it neater.

Bear in mind though plastic expands and on a 13 meter run could get a bit wavy.
Until you calculate the SWA size, its unknown whether it will fit in 25mm conduit which is the biggest readily available, an alternative is 40 or 50mm square trunking, but you dont seem to get nice joint peices.

I took it that your taking 23 metre supply from house CU, then go on to say the hot tubs in the garage and close to the CU for isolation so im confused.

As for the extra earth rod, I may be wrong but youd create an Extroneous Conductive part and would then require a larger earth bond from the house.
As above, you need someone knowledgable on board to run your ideas by and assist them

Rock on george ready for summer

 

[JohnW2]

As for the extra earth rod, I may be wrong but youd create an Extroneous Conductive part and would then require a larger earth bond from the house. ... As above, you need someone knowledgable on board to run your ideas by and assist them

I don't count myself as particularly knowledgeable but, yes, I agree with you that the export the house earth and also to have a local earth rod would seem make little/no sense - as you say, the earth rod would then be an extraneous-c-p which would require adequate bonding to the house's MET. I would have thought that the question which might be debated is whether to TT the tub - i.e. have a local earth rod instead of an exported earth - and the electrician undertaking the work will undoubtedly have a view about that.

Kind Regards, John.

 

[bernardgreen]

If the supply to the house is PME ( earth derived from the neutral ) then I would NOT export the PME earth to the tub. The supply to the tub would be TT with a effective ground rod and RCD protection.

The reason is that the PME "earth" is the neutral of the supply network and this will have voltage drops between the house and the sub-station. Hence the PME "earth" may be a few volts different to the ground around the hot tub.

If the supply to the house is TN-S ( a separate earth wire to the sub-station ) then unless there is a fault there would be no current flowing in the earth to the substation so no voltage drop to lift the earth at the house above the ground around the hot tub. So the house earth could be exported to the tub.

The other way to look at it is that exporting the house earth to the hot tub effectively puts the hot tub into the equipotential zone of the house. The ground around the tub would be an extraneous potential source and would there for need to be bonded. A single earth rod would be un-likely to be able to "bond" all the ground under and around the hot tub to the requirements of a PME equipotential zone.

A single rod ( provided it had a low enough impedance ) would be adequate to ensure an RCD would trip on a earth fault in the tub installation.

 

[JohnW2]

A single rod ( provided it had a low enough impedance ) would be adequate to ensure an RCD would trip on a earth fault in the tub installation.

Indeed. On would expect an earth rod to provide a path to earth no more than about 100Ω (and >200 Ω would not be regarded as acceptable), but anything less than about 7,667 Ω would be adequate to ensure that an RCD operated in the event of an L-E fault.

Kind Regards, John