Hot tub load

[plancaster]

Hi Every one hope you are all well.
A customer has asked me to install some swa to a shed to run 2 sockets and a couple of lights all well and good but he dropped into the conversation that he was thinking of putting a Hot tub in at a later date but he dose not know you what size hot tub he would buy has any one got any advise on what extra capacity I should allow for the swa.
Thanks
Phil

 

[SJD]

Many hot tubs require a 32A or even 40A supply, on their own circuit.

And eventually when deteriorating insulation resistance causes the RCD to trip, you'll be glad it is on its own RCD / RCBO.

 

[telectrix]

6.0mm SWA should suffice unless the hot tub is a ridiculous power. might be best to get him to sdvise on the hot tub he's considering before calculating.

 

[plancaster]

Hi The plan is to take the feed from the consumer unit before rcd fed from a mcb to the shed then the swa to a garage consumer unit that will have rcd and the shed and the hot tub earthed as a TT system just wondering on the extra capacity to allow for if he adds a hot tub was thinking of 6mm 2 core swa
Phil

 

[telectrix]

why TT? otherwise the 6.0mm SWA on a 40A MCB sounds good unless the hot tub will be over 32A, i which case i'd go for 10.0mm on a 50A. end of the day, you are in the dark unless he knows the power requirements of the tub.

 

[plancaster]

well my thoughts are that by doing it the way I have suggested would make the shed and the hot tub wiring separate from the house in case there was a problem with the outside electrics but I am open to a better solution I was thinking of stating on the calculations that I have allowed enough for a 32A tub so that if he buys one then he will have a limit
phil
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as another thought what is I put 4mm 4core swa then if he puts a hot tub in them have 2 lines and 2 neutrals Just a thought
phil

 

[telectrix]

as another thought what is I put 4mm 4core swa then if he puts a hot tub in them have 2 lines and 2 neutrals Just a thought phil

bad idea. you'd need to feed that 4 core from 2 separate breakers. better to use 6mm 3 core and limit his tub to suit.

 

[plancaster]

It would not be ideal can I ask you why 3core swa as I would only need line and neutral as the shed would TT Just I might be missing some thing
phil

 

[telectrix]

but why TT?

 

[plancaster]

as if there is a problem with the outside electrics and it would trip the rcd in the garage consumer unit located in the shed as apposed to the electric in the house as the connections in the house consumer unit would be before the rcds
phil

 

[Lucien Nunes]

The earthing method doesn't affect what RCD(s) trip for a given fault location.

 

[SJD]

You don't need to use a TT earthing to have the RCD in the shed. I would suggest having a separate RCD for the hot tub - so possibly make the shed consumer unit an all-RCBO unit.

Also, you haven't mentioned how far this shed is from the house, so nobody has queried whether the cable size is determined by the current carrying capacity, or instead by the voltage drop.

 

[plancaster]

Good point the shed is 17meters away the reason I was doing the shed as TT is because the hot tub would need a rod so I thought it would be best to do the whole shed separate so would you all think it best to use the earthing facility of the house I am open to better segestions than the one I have thought of
phil

 

[davesparks]

as if there is a problem with the outside electrics and it would trip the rcd in the garage consumer unit located in the shed as apposed to the electric in the house as the connections in the house consumer unit would be before the rcds
phil

Can you expand on how you think this relates to creating a seperate TT system?

Are you confusing the recommendation about earth electrodes for an outdoor pool/hottub with creating a seperate TT system?

 

[telectrix]

plug-in hot tubs come with a fitted 10mA RCD. i suggest that if the one he gets does not have one, then fit a 10mA RCBO in the garage/outhouse CU specifically for the tub.

 

[plancaster]

Yep I believe that I am how would yous recommend the installation be

Phil

 

[plancaster]

Hi guys I am open to ideas on the install would you think it better to take line neutral and earth from the consumer unit to a garage consumer unit then split off to the diff circuits
phil