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Domestic Hot tubs....

Discuss Hot tubs.... in the Electrical Forum area at ElectriciansForums.net

keniff

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Arms
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So hot tubs, would you use the pme supply and get that slight tingle when getting out or rod it? Can't find a reg on it so it's a bit unclear. Your thoughts please!! :)
 
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Strima

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Esteemed
All depends on the installation, cable run etc and manufacturers instructions. Seen quite a few hot tubs but no stakes in.
 

keniff

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Yeah see iv acquired one, no instructions etc, wired it with swa to mini consumer unit built in the tub, using the provided pme tncs earthing. I don't get a tingle but the mrs does lol
 
D

Dcf

I've just done a big swim spa on a three phase pme connection,
The regs state that if it's pme then it requires an earth rod with a resistance of 20 ohms or less .its tucked away in the special locations bit about pools.
ive also seen plenty without rods though.
 

Strima

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The regs state that if it's pme then it requires an earth rod with a resistance of 20 ohms or less
That's going some with rods to get it down that low, I know it is possible but come on, 20 ohms, would end up spending more on rods than anything else.
 

keniff

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I've just done a big swim spa on a three phase pme connection,
The regs state that if it's pme then it requires an earth rod with a resistance of 20 ohms or less .its tucked away in the special locations bit about pools.
ive also seen plenty without rods though.
Just found that reg, it says when pme is used to supply the pool or basin it is recommended to use a rod for equipotential bonding, that would mean the frame etc would be on a rod and pme? Surely it's one or the other?
 
D

Dcf

Just found that reg, it says when pme is used to supply the pool or basin it is recommended to use a rod for equipotential bonding, that would mean the frame etc would be on a rod and pme? Surely it's one or the other?
That was my thoughts exactly.
i ran a 10 mm earth wire from the db to the pump unit and another 10mm from the unit to the rod.i got it down to 23ohm at the rod end.its in the regs for a reason I suppose but it's not that clear what that reason is.good old wiring regs you would think that after 17 editions it would be black and white though instead of a murky shade of grey
 

keniff

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So you had pme and TT connected together? Strange but that's how I read it also. Might just bang a rod in doubt I will get it down to 20 in my area but it's only a "recommendation" I suppose
 

spark 68

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Esteemed
While looking through GN7 (for something else) hot tubs are mentioned in chapter 13 of GN7 amd1,
it says basically where a hot tub is in a room other than a bathroom then section 701 (location containing a bathroom or shower) is to be applied in full.

Where the hot tub is located outdoors then section 702 (swimming pools etc.) applies in full.
Wrt 702, supplementary bonding is required for all extraneous conductive parts in zones 0,1 and 2 irrespective of whether they are simultaneously accessible or not.
 
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E

Engineer54

Very much depends on the location and what the tub is mounted on. If you have positioned the tub on bare ground/grass, then your asking for trouble!! The best mounting/positioning is on a hard wood decking base, with a decent distance of surrounding decking. Concrete or concrete and slabs is only a little better than bare ground, especially if there is reinforcement in the concrete.

Nothing wrong at all with combining a rod to a PME supply. What i have to laugh at though, is that your BS7671 calls for a 20 ohm Ra on a hot-tub with a PME connection, but 200 ohms on a TT system covering the whole installation!!! It's not as if 20 ohms is going equal out, say a 0.35 ohm PME earthing. I know what they are trying to do, but you'ld be Better of making the hot-tub a TT and be done with it, but not a 200 ohm TT...lol!!!
 

spark 68

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Esteemed
Hi E54,

As far as PME goes, I think this probably the time to consider TTing it, as you would for caravan pitches etc.

Edit: just read your post saying basically the same thing, lol
 

keniff

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Well it's on a concrete base untill decking goes down, I'll bang a rod in but best I get in this area is about 100 with a few rods! Thanks guys
 
E

Engineer54

Well it's on a concrete base untill decking goes down, I'll bang a rod in but best I get in this area is about 100 with a few rods! Thanks guys
You surprise me, What area of East Sussex are we talking about??
 

keniff

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Hastings it's very rubbly here seem to get nice readings in the what i think clay areas, but not alot are TT around here
 
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Englishsparks

IS the Mrs insured?

If so dont worry about.


Seriously! I would follow the manufacturers instructions, so why not google it for the info.

Yeah see iv acquired one, no instructions etc, wired it with swa to mini consumer unit built in the tub, using the provided pme tncs earthing. I don't get a tingle but the mrs does lol
 
E

Engineer54

Hi E54,

As far as PME goes, I think this probably the time to consider TTing it, as you would for caravan pitches etc.

Edit: just read your post saying basically the same thing, lol
It's not so much the PME, more in the fact that a person with wet bare feet on bare ground or a conductive concrete, that is at or near to true ground potential, with an electrical ground potential also being present. There is a chance (remote maybe) of a step voltage between the two potentials....

The chances of a broken neutral on the PME, i wouldn't particularly consider, you'll be lucky to see one real instance in a lifetime...
 

keniff

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Thanks for all the replies found a sticker on the tub to earth rod the install, 3 rods smacked in the ground later got it to 13ohms..... Dipped my hand in to check water temp and I got a tingle!!! Think i have narrowed it down to heater leaking to earth a little so I'm going to ir the element tomorrow and more importantly not use it for now lol
 
E

Engineer54

Sounds as if you have an American hot tub there, if you have found a sticker to that effect. American hot tubs often come with a supplied 8 foot earth rod when new...
 
G

Guest55

Sounds as if you have an American hot tub there, if you have found a sticker to that effect. American hot tubs often come with a supplied 8 foot earth rod when new...
You'll have fun banging in a 8 ft rod if ts in a single length lol.
Sledge-hammer on stepladders anyone ? :)
 

keniff

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  • #21
Right to all of those interested I have tried the rod and pme and you get a tingle and now have made the tub TT and tingle has gone, rod is 13 ohms so all good to go! Must be a slight potential difference between true earth so to speak and the suppliers earth, that's all I can think of....
 

keniff

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  • Thread Starter Thread Starter
  • #22
It's not so much the PME, more in the fact that a person with wet bare feet on bare ground or a conductive concrete, that is at or near to true ground potential, with an electrical ground potential also being present. There is a chance (remote maybe) of a step voltage between the two potentials....

The chances of a broken neutral on the PME, i wouldn't particularly consider, you'll be lucky to see one real instance in a lifetime...
That's what I was trying to say lol didnt realise you has already said it :)
 

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