Hot tub installation questions

[mcquitmp]

Hi,

I am thinking about installing a hot tub in the garden and I have a few questions.

The hot tub in question apparently requires a 32A RCD. It has a 5.5kw heater and a number of other items / pumps which I am sure contribute to the majority of the 32A load - but i suspect it does not draw the full 32A and certainly not all the time as not everything will generally be on at the same time.

Q1 - What size of SWA cable do I need ?. The run is about 42m long - but may end up being a little more. The cable would run up and down the outside of the house and through the loft space - followed by a few meters buried in the ground. I think I might be on the verge of 6mm2 cable and 10mm2 as I think the breakpoint is quite close. I presume I need 3 core cable.

Q2 - The hot tub is wired by means of connecting to a small control panel - outside that panel there is earth bonding lug. Do I need to bond the tub to earth using that lug? I can't think why as the tub will be sunk into a deck and the only open access would be the acrylic shell and stainless steel jets - but they are probably fed with plastic pipes - so where is the risk?

Q3 - If I need to earth bond the tub - how do I do it - what do I bond it too? - given the earth cable (as part of my 3 core cable) has just been terminated internally in the control panel? Do I need to provide a separate earth spike and bond the tub to that?

Q4 - I plan to run the SWA cable to a weatherproof isolator switch about 2m from the tub. Can you recommend a good switch for that? and I presume its best to go for non metallic switch to remove any earth requirements there as well?

Q5 - Do I have to use SWA cable all the way to the tub - or can I switch to other cable from the isolator switch onwards? It only needs to go below ground leading up to the switch.

Thanks for your help...
Maurice

 

[Chri5]

Hi,

I am thinking about installing a hot tub in the garden and I have a few questions.

The hot tub in question apparently requires a 32A RCD. It has a 5.5kw heater and a number of other items / pumps which I am sure contribute to the majority of the 32A load - but i suspect it does not draw the full 32A and certainly not all the time as not everything will generally be on at the same time.

Q1 - What size of SWA cable do I need ?. The run is about 42m long - but may end up being a little more. The cable would run up and down the outside of the house and through the loft space - followed by a few meters buried in the ground. I think I might be on the verge of 6mm2 cable and 10mm2 as I think the breakpoint is quite close. I presume I need 3 core cable.

Required Cable Size 10mm

Voltage Drop 6,6volts.

Percentage Drop 2.9%.

Load = 34.9 amps.

Q2 - The hot tub is wired by means of connecting to a small control panel - outside that panel there is earth bonding lug. Do I need to bond the tub to earth using that lug? I can't think why as the tub will be sunk into a deck and the only open access would be the acrylic shell and stainless steel jets - but they are probably fed with plastic pipes - so where is the risk?

Refer to manufactures instructions and do as they say. Thinking isn't allowed

Q3 - If I need to earth bond the tub - how do I do it - what do I bond it too? - given the earth cable (as part of my 3 core cable) has just been terminated internally in the control panel? Do I need to provide a separate earth spike and bond the tub to that?

There's various ways to do this, from the glanding off on the SWA- but your sparks will know best for local conditions.

Q4 - I plan to run the SWA cable to a weatherproof isolator switch about 2m from the tub. Can you recommend a good switch for that? and I presume its best to go for non metallic switch to remove any earth requirements there as well?

Mk and various others offer suitable switches, I'd also think the hot tub instructions would have further suggestions. Again I'd suggest advice via a sparks on site.

Q5 - Do I have to use SWA cable all the way to the tub - or can I switch to other cable from the isolator switch onwards? It only needs to go below ground leading up to the switch.

Your choice and more dependent on site conditions, artic cable and most 2.5 flex is rated to 24/25a-
I'd still go with correct external cable. HiTuf 2.5mm is £2.20 at meter, and you don't want broken / breaking down cable near your tub

Thanks for your help...

Nice to offer thanks and good manners.

The work is notifiable / Part P job- I'd suggest you consider doing the cable run and then commission a sparks for a few hours to finish off the job / terminate and certificate.

3 core 10mm x 50m drums = £200 inc VAT via TLC

 

[mcquitmp]

Chris,

Thanks very much for the reply...a couple of comments below...

Q1 - I'm gutted to find out it 10mm2 rather than 6mm2 - makes it a lot more expensive. Are you really sure of the sums on that - The reason I ask is that I tried using a calculator on some site and it seemed to suggest the break point between the two was about 44m and I was thinking of doing a more exact measurement on the distance etc and hopefully coming in at less that 42m. What do you make the breakpoint in terms on distance? Although I suppose its best to be safe than sorry.

Q2 and Q3 Unfortunately Hot tub instructions not very helpful. In the objective to connect their earthing lug to the earth of my supply. If thats the case then me connecting the earth from my 3 core to their control system would have done that would it not? I thought perhaps the lug was to earth bond to other metallic devices in the vicinity - but i wont have any there for it to connect too.


Q5 - Don't I need to continue with 10mm2 cable all the way to the hot tub with regard to Q1?

I was thinking of doing the job myself and getting the Local authority to inspect - but I can see the sense in your suggestion - take out the hard labour myself and get them to do and certificate the rest. I was quoted £435 for the job which I felt was excessive - but if it really needs to be 10mm2 at £200 then maybe its not too bad. I do have some experience as I trained as a spark in a factory many years ago and then changed direction - sadly I'd need a refresher on all the regs and I don't have much practical experience.- but at £435 for a job like this it does make it think I ought to do a bit of retraining.

Many thanks for your advice so far...
Maurice

 

[Chri5]

Taking the load figure (5.5 kW )you would get away with 6mm up to about 48m.

The cable could cope with 24a, so the fuse and RCD would have to be down rated (against your manufactures instruction) to 20a.

It's not for me to say if this will cause problems, but the bottom line is that the 'false' economy isn't worth while.

Your end up wanting music, lights (so the neighbours don't have to listen to your singing), so go with 10mm.

If you take the earth via the correct glands from the SWA 2 core would suit.

Prices via TLC (I'd quoted 3 core before):-

£107.70 + VAT for 50m 10mm 2core SWA via TLC, approx £127.

I'd also think about having a double external socket for music power, and maybe even a lighting position or two.

As you know the SWA 10mm is to the localised isolation / RCD. The 6mm could cope with the load, but can't cope with the fuse design rating so the cable must be rated higher.

10mm will cope with 9.5kW / 40a odd x 50m run, hence why cable between RCD and tub can be smaller than 10mm. This also give capacity for lights and power socket local to the tub via a mini / workshop / CU.

Something like
http://www.tlc-direct.co.uk/Products/MK5704.html

If you did all the leg work (dig, cable, position switches), get a sparks to commission the job, his materials (CU / RCD /MCB's glands) would be sub £100 and half a days work- London rate £150' ish

If you do the work, it's same cost for the sparks supplied materials plus £125+ LBC fee's, so go with the sparks.

Maybe an ex colleague could do the work if any have kept up the trade / training?

 

[mcquitmp]

Chris,

Many thanks again. I hadn't appreciated that you proposed a localised CU meaning a couple of RCD's in circuit - but I can see that makes sense as I will have some flexibility in the future. The Hot Tub says it must be the only device in the RCD circuit - so your arrangement does neatly get round that and provides pleasant relief for the neighbours (you must have heard my singing!!!).

Unfortunately my ex-colleagues are in Northern Ireland - unless one of them wants a cheap trip to Ipswich that won't be possible.

I think I favour the spark route now with me being his apprentice - rather that the LBC as I've just heard their fee is £100 plus VAT.

I don't mind paying a fair price - everyones got to make a living somehow.

Regards...
Maurice

 

[RF Lighting]

Split concentric cable is smaller and cheaper than 3core SWA, and it also does not require special glands.


The normal switch used on hot tubs is a rotary isolator

 

[Lectrician]

And there is no reason to mount the switch at waist height or above - keep it 300/450 from the floor! Keeps it all neat and tidy!