Where/how to plug in my portable hot tub?

[magictime]

...maybe I should spell out the geography of this in a bit more detail in case that makes a difference to how people are perceiving this.

When I talk about drilling holes in walls & trailing cables through them, I'm not talking about my living room! My house has a small extension at the back that we use as a utility room and bike store; almost an outbuilding really. The proposed hot tub site is just the other side of the back wall of that room. That's the wall I'd be talking about drilling through - either to bring the hot tub cable indoors to meet an indoor extension, or to take the cable from an outdoor socket kit outside.

 

[mikhailfaradayski]

HI Magictime,

Any chance you could indicate the model/type of hottub?

There is guidance to suggest that permanently connected equipment exceeding 2kW should be fed from its own dedicated circuit.

I think you over-estimate the amount of disruption caused when you talk about sparkies knocking holes in walls.
Given the way you describe the installation, i think it may not be that painful to the wallet to get a spark in to put his eyes on the job and provide a good, permanent solution.

Do you intend to do this job properly? (not a sarcastic comment)
If so, have you considered the hoops you have to jump through regarding notification to LABC of this work?

 

[SUNRAY]

An RCD supply means you can ditch the RCD plug. Given the length of time the heater will have to be on I would strongly suggest using a 16A IEC 60309 plug, and the use of (for example) an IP rated MK Commando socket.

Why's that then BAS, oh don't tell me you have suddenly changed your mind and decided 13A plugs are unfit for purpose.

 

[ban-all-sheds]

- hmm... can't help thinking somebody would have noticed if this was the case. Typical customer experience seems to be that it takes about 7-8 hours to get the water heated initially,

Well - typical customer experience is one thing, and the fact that the specific heat of water is 4.19J/gK is another.

You've got a 1.5kW heater, and 800l of water.

In a 7-8 hour period, the former will deliver 37,800,000 - 43,200,000 joules.

The latter will therefore increase in temperature by

37800000/(4.19 x 800000) to 43200000/(4.19 x 800000) °C

i.e. 11.3 - 12.9°C

I believe that a mains water temperature of 10°C is commonly assumed, but lets say that in the summer it gets up to around 15°C?

Your hot tub, assuming absolutely perfect insulation, i.e. no heat loss at all during the heating process, will end up at 26 - 28°C.

I don't know what kind of hot tub experience their typical customer likes, but I can assure you that 26 - 28°C is not hot enough by a considerable amount.

 

[ban-all-sheds]

Why's that then BAS, oh don't tell me you have suddenly changed your mind and decided 13A plugs are unfit for purpose.

It's not so much that they are unfit for purpose as they are less fit than some alternatives.

Don't forget - at the time the load was assumed to be 3kW (i.e. right on the maximum), and would be running for several hours. Under those circumstances I see nothing wrong with saying that an IEC 60309 would be better.

 

[slup]

I don't know what kind of hot tub experience their typical customer likes, but I can assure you that 26 - 28°C is not hot enough by a considerable amount.

I have a permanently installed hot tub and it feels nippy if the temperature drops below 36°C - certainly wouldn't even contemplate getting in at 26 - 28°C. I keep it at 38.5°C.

Mine draws 7.6kW with everything on full tilt. It is, however, ridiculously well insulated and costs less than £10 per month to run.

The heater is 2.75kW and it's an overnight job to heat 2000 litres of water from tap temperature to 38.5°C. I haven't ever timed it exactly, but if I fill it on an evening, it's ready by the morning.

 

[magictime]

HI Magictime,

Any chance you could indicate the model/type of hottub?

- It's an MSpa Camaro (B-130)

There is guidance to suggest that permanently connected equipment exceeding 2kW should be fed from its own dedicated circuit.

I think you over-estimate the amount of disruption caused when you talk about sparkies knocking holes in walls.
Given the way you describe the installation, i think it may not be that painful to the wallet to get a spark in to put his eyes on the job and provide a good, permanent solution.

- maybe I should check with an electrician, but from past experience I find it hard to believe a new circuit is going to get wired in - leading up from the CU downstairs in the basement kitchen, through the utility and out the back of the house - without some sort of fairly major headache in terms of ripping walls, floors & ceilings to bits.

Do you intend to do this job properly? (not a sarcastic comment)
If so, have you considered the hoops you have to jump through regarding notification to LABC of this work?

No, I haven't to be honest - I haven't been thinking of this in terms of a wiring job at all, just in terms of plugging in a new appliance. I guess that's something else to look into.

BAS - re length of time to heat: right you are - manufacturer even states rate of heating as around 1.5 - 2 degrees an hour (meaning temp in the 20s after 8 hours), so yes, the reviews I've been relying on are plainly written by people with distorted time perception.

*sigh*... more and more inclined to think that if it really is going to take a sledgehammer to crack this nut, I might just skip the nut & cancel my order.

 

[magictime]

NB previous post is confusing - I've replied to queries within the text of the quote. Sorry!

On heating time - sounds like the actual figure would be about midway between the 8 hours suggested by dodgy reviewers and the 24 hours minimum that was your original guesstimate, BAS.

 

[ban-all-sheds]

1.5-2 degrees an hour with a 1.5kW heater implies that you might not fill the tub to capacity.

800l of water will rise in temperature by 1.6°C if you put 1.5kW into it for 1 hour and there are zero losses.

My original estimate was for the full 800l, a 30° Δ, and a fudge factor for losses, and it's not far off the makers own worst case of 20 hours.

 

[ban-all-sheds]

My house has a small extension at the back that we use as a utility room and bike store; almost an outbuilding really. The proposed hot tub site is just the other side of the back wall of that room.

So how much effort would it be to extend the socket circuit to supply an external socket on that wall?

 

[magictime]

BAS:

"So how much effort would it be to extend the socket circuit to supply an external socket on that wall?"

Possibly very little (though won't it depend on whether there are existing spurs?)... that's definitely my favoured option at the minute if any kind of extension lead/outdoor socket kit option is a no-no.

 

[LoveRocket]

For crying out loud, what is going on here?

OP - Are you saying that you have a hot tub that is sat outside your back wall and you want to plug it in?

Find a socket on the inside of the back wall. Take it off and remove the backbox.
Drill a hole in the wall.
Mount a weatherproof socket on the otherside and run the cable through.
Refit the backbox, connect all the cables and refit the socket.
Remove the RCD plug from the hot tub flex and fit a normal one (as you are sure the socket circuit is 30mA RCD protected...)

Plug the hot tub in.

 

[ban-all-sheds]

Find a socket on the inside of the back wall. Take it off and remove the backbox.

1) I get the impression that there isn't one on that wall.

2) There are the Zones around the tub to consider.

 

[LoveRocket]

2) There are the Zones around the tub to consider.

What do you mean? (genuine question)

I was under the impression that the OP has a hottub plocked in the back of his yard, with a trailing flex that will plug in when he wants to use it. Are you talking about specific rules about hottubs and suchlike used outdoors?

 

[magictime]

For crying out loud, what is going on here?

OP - Are you saying that you have a hot tub that is sat outside your back wall and you want to plug it in?

Find a socket on the inside of the back wall. Take it off and remove the backbox.
Drill a hole in the wall.
Mount a weatherproof socket on the otherside and run the cable through.
Refit the backbox, connect all the cables and refit the socket.
Remove the RCD plug from the hot tub flex and fit a normal one (as you are sure the socket circuit is 30mA RCD protected...)

Plug the hot tub in.

"Find a socket on the back wall"... simple as that eh? Alas, there isn't one. Hence all the hoo-ha about extension cords, wiring work etc.