Hot tub supply

[Bradley6969]

Hi, having new hot tub installed, PME supply on 40A breaker 6mm twin clipped direct in loft down to 32A isolator, got some 10mm 2C laying around, and gonna use swa as earth from isolator will that be fine, (thought I’d ask not sure what these companies are like and I’m not around when they install so gonna lock off isolator and breaker and leave key for them)

Thanks

 

[Strima]

32A iso on a 40A circuit?

 

[telectrix]

what's the rating of the tub?

 

[Bradley6969]

32A iso on a 40A circuit?

Sorry actually on 32A breaker

 

[Bradley6969]

what's the rating of the tub?

Just says 32 amps, has 2kw heater all I can find

 

[telectrix]

that's only 10A. usually fitted with a 13A plug and inline 10mA RCD.

 

[Bradley6969]

that's only 10A. usually fitted with a 13A plug and inline 10mA RCD.

yes, must be all the jets aswell as there’s a few of them and heater once all switched on together

 

[Sparky Pat]

think you will find that you need to take it off the PME system and make it a TT system.

 

[Bradley6969]

think you will find that you need to take it off the PME system and make it a TT system.

Why’s that

 

[D Skelton]

I'd be breaking the earth on a PME and rodding down adjacent to the tub. 8 foot coupled rod. Small non-conductive four way external IP rated board with a 10mA and a 100mA s-type RCD in line. Rotary isolator mounted adjacent to the board. Take off a non-RCD way at the supply DB.

If you want a proper job that's the safest way to do it.

 

[Sparky Pat]

Why’s that

to stop you getting a shock if you lose the neutral,

 

[timhoward]

Why’s that

Also as a couple of threads have reported tingling feet when getting out due to potential difference of real earth and PME earth.

 

[pc1966]

I'd be breaking the earth on a PME and rodding down adjacent to the tub. 8 foot coupled rod. Small non-conductive four way external IP rated board with a 10mA and a 100mA s-type RCD in line. Rotary isolator mounted adjacent to the board. Take off a non-RCD way at the supply DB.

It is a dedicated supply to the hot tub so RCD selectivity is not important but I agree 100% that having two in series for no single point of failure is a good idea. Just take the supply off the usual RCD or RCBO in the house CU, but have a 2nd double-pole RCD out at the tub and a local rod.

Depending on the soil you probably don't need an 8' rod, if the usual 4' style is measuring below 200 ohms then it is fine. Often you can extend the rod by another 4' using the threaded coupled if it turns out to need it. Just take care/inquire about any buried services before hammering one in!

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You can use a metal IP rated mini-CU such as this:

Metal Garage or Shower Unit IP65 Empty Body

Neutral and earth terminals, DIN rail, neutral cable and busbar included

www.cef.co.uk

You don't need to use the matching RCD, though that is convenient, as you are using it as a DIN enclosure so no specific busbar alignment to worry about. The enclosure body would be on the local TT earth, so any SWA entering it should have a plastic IP68 style of gland for support/weatherproofing to keep it electrically isolated from the supply PME earth on the armour.

 

[D Skelton]

It is a dedicated supply to the hot tub so RCD selectivity is not important but I agree 100% that having two in series for no single point of failure is a good idea. Just take the supply off the usual RCD or RCBO in the house CU, but have a 2nd double-pole RCD out at the tub and a local rod.

Due to the sensitivity of a 10mA RCD that's why I suggested having it seperate to other RCDs in the installation and dedicated only for the hot tub. The 100mA s-type will delay tripping in the event of a failure of the primary and although it would never meet regulated disconnection times it would serve as a last line of defence only. You would still need to have a primary RCD to meet the requirements of discrimination.

The best way would be a dedicated circuit RCD protected at or near the point of use.

Depending on the soil you probably don't need an 8' rod, if the usual 4' style is measuring below 200 ohms then it is fine. Often you can extend the rod by another 4' using the threaded coupled if it turns out to need it. Just take care/inquire about any buried services before hammering one in!

The only way you can guarantee the seasonal stability of a rod is with depth. 4' rods are next to useless for providing stable earth fault paths. Resistance is ultimately a moot point. 200 ohms is a recommendedation only. What matters is that the value won't fluctuate. A 4' rod in the wrong soil type and a dry season can easily see 1667 ohms exceeded.

Agreed on the buried services though.

You can use a metal IP rated mini-CU such as this:​

You don't need to use the matching RCD, though that is convenient, as you are using it as a DIN enclosure so no specific busbar alignment to worry about. The enclosure body would be on the local TT earth, so any SWA entering it should have a plastic IP68 style of gland for support/weatherproofing to keep it electrically isolated from the supply PME earth on the armour.

I recommended non-conductive for a reason. The more you limit simultaneously accessible exposed conductive parts on an installation like this the better. Also, it leaves no chance for a path to present itself between the supply earth and the sub circuit earth. Personally I wouldn't be using SWA as it's unnecessary. I'd likely be using HO7.

There are plenty of non-conductive ABS products on the market that meet the regs for fire resistance. Alternatively, a plastic IP rated external board could always be fitted and recorded as a departure from the regulations and justified using its location and its provision of increased protection from electric shock.

 

[littlespark]

Do we know what type of hot tub it is? Many are marketed as plug n play, so it’s plug it in and bobs yer ma’s brother.

we’ve had this discussion so many times before.... but basically, if it comes with a plug on it, all you need is an outside socket.

id only worry if you were stepping out into a metal decking.

 

[D Skelton]

I don't think the plug and play sets are fit for human use IMHO. Death traps waiting to strike.

 

[timhoward]

I do wonder if one of the hot tub threads should be a sticky, as it seems that every week there's a hot tub project.