The dirty sex pool has just been ordered.

It’s 25 amp, so I need to get supply to the garden. CU is in the middle of the house with 18 inch stone walls (can’t drill through!). Garage is detached and is powered by a spur from the 13 amp kitchen sockets, only has lighting and sockets circuits but I do use a welder and washing machine and power tools etc. So I want to put on a better supply.

So plan to run swa from CU out and around the house, under the drive in an existing channel to the garage. Fit a new CU in the garage to feed the garage circuits and take a supply from that to the new hot tub.

About 30m to the garage, then 50m to the tub. Combination of clipped to wall and buried 450mm with warning tape etc.

Thinking 6mm to garage then 4mm to tub. Does that sound about right? Will fit 60amp breaker at house CU on the RCD protected side, with 30 amp breaker to tub and the usual light and sockets breakers.

I’ve done a fair bit of sparking before including fitting CUs and new circuits. But given current (sorry!) regs I’ll probably get a local spark in to do the connections and test just to be certificates, and I’ll run the cables and mount the isolator and CU etc.

Might be as cheap just to buy 100m of 6mm SWA and use that throughout.

Thanks in advance.

I would go with 6mm

I would go with bigger than 6mm for the Garage supply and 6mm for the pool supply, but I’m an amateur who is a bit cautious.

You need to take voltage drop into account. Calculator link
I think that 6sqmm over 80m is probably on the limit for the tub alone, never mind the garage
I’d consider a 60A circuit breaker too high for 6sqmm cable as described

10mm SWA supply might cover you for future shinanigans. Probably better though to get your local sparks to do the calculations, tell you size of cable, supply isolator, breakers and so on, then you do the digging donkey work knowing he’ll definitely sign for it.

difference in cost between 6 & 10mm SWA is minimal compared to the hassle of running it in.

Try and get hold of a PDF of the wiring regulations. Even if it is not the latest amendment the calculation for cable sizing will be the same. It will have all bits you need from downgrading for installed in insulation etc

10mm2 armoured cable buried is rated at 60Amps. Voltage drop depends on loading but assuming a full 60A over 30m it will drop 7.92 volts. The regs. say that 3% voltage drop for lighting circuits is considered to be permissable which is 6.9 volts so you’re dropping more than you should given the lights in the garage. In practice it’s probably unlikely that it will be a problem as you’ll not be pulling anywhere near 60A except for short periods.

16mm2 over 30m at 60A drops 5 volts so good for the garage lights. 50m of 10mm to the tub will drop 5.5 volts at 25A. Assuming full loads the total drop to the tub will be 10.5v which is within the 5% drop suggested for non-lighting stuff. 6mm to the tub would drop 9.75v so cumulatively it’s too much.

These are worst case figures at 60A. A 50A mcb would just allow you to get away with 10mm throughout.

I’d go 16mm to the garage and 10mm to the tub. As said above, the cable is cheap compared to having to size up if you get it wrong.

You may struggle to get a 60A MCB, it will depend on the make of the board. 50A is more common and would fit in a normal consumer unit. 60A may require you to split the incomers to a separate enclosure with a breaker in it.

Don’t put the distribution circuit on the RCD protected side unless you have a TT earthing system in which case it should be a 100mA time delayed one or if it is unarmoured and runs less than 50mm deep in a wall in which case it will have to be a 30mA one.

The 30mA RCD for shock protection should be located in the garage where it can be easily reached to reset if it trips and also won’t take down any circuits in the house.

If you’re earthing is PME, I’d suggest an earth rod at the garage.

Yes, I’m an electrician and happy to answer any questions but the normal caveat applies in that I’m not on site so no liability accepted – it’s info only.

Rich.

Thanks for the replies all, especially Rich for the detailed explanation.

I can get pricing up cable and mcbs/CUs now, will get a local guy in I reckon to confirm that he is happy and get him to do the connections.

They suck electricity! I took a separate feed into the adjacent shed then a nice little cu in there with 2 ways, one for the tub and one for the soon to be constructed summer house. Also fitted a rotary isolator on the wall behind the tub so it’s easy to kill and done properly.

Wrightyson – yeah, had a tub at the last house in Belper. Was swa with rotary isolator etc. All fitted by myself but it was a straight easy short cable run. This ones a bit longer so got more to consider.

Been in Wales a couple of years without a tub. The Mrs has a neck injury and the tub helps, and we have proper big dark skies, so missing it now, hence the purchase

The house move I’d also love to do! Enjoy the tub!

Whereabouts in Wales are you?

An update given the helpful replies….

Local spark (cyclist too!) recommended 16mm2 to the garage CU then 10mm2 to the tub, tallied with rwmartin which was reassuring.

Ended up taking a feed directly from the main house feed via 100amp isolator next to house CU, into to the garage (means the house isn’t affected if there is a trip on the tub/garage circuits) into RCD protected new CU to bring the garage up to date. 25amp breaker to the tub and new breakers to the lights and sockets in the garage.

I did all the cabling, wired up the garage CU etc and the spark did connections around the house CU and tested and signed off.

All perfect.

@rwmartin – missed your last question – just outside Llandrindod Wells.