UK 32a supply for a hot tub of a PME supply.

[davesparks]

I'm not replying on them solely but every day is a school day

Indeed, and watching people work is a great way to learn practical methods and techniques, tips and tricks etc.

For technical information and knowledge you need to make sure that what is being presented by uncontrolled sources is actually correct and not just someone opinion or own misunderstanding being presented as fact.

Everyone makes mistakes, this includes people on YouTube.

 

[suffolkspark]

The way I read the regs is its fine on pme if you can supplement it with a rod etc under 20ohm. I have recently achieved this on a couple of rods but dont often, so I always opt to seperate it off the pme

 

[Mark.fardon]

Because every electrician on YouTube says you do

You may roll your eyes and maybe every electrician on you tube does suggest/do this.
But that doesn’t make it a good idea necessarily. The regs suggest as “recommendation” in a PME supply to provide an earth electrode < 20 ohm for a swimming pool supply. But do a risk assessment- are there any exposed conductive parts liable to be touched by the user of hot tub (likely to be class 2) ? Is it an overhead supply /rural installation ? What is the likelihood of a lost neutral in the supply ? In the event of the lost pen conductor is the bonding to water and gas in place and reliable ?

Weigh up pros/cons of using the DNO earth and bonding any extraneous conductive parts (Using 3 core SWA, marshalling terminal if required) and having a Ze of 0.2 Ohm, having protection by ADS fault protection and additional protection via an RCD ...or isolating this excellent earth , having a variable earth rod Ra of 100 ohms plus in most cases and relying solely on an RCD to achieve fault protection disconnection time in 0.4s. A rod and connection that could be damaged outdoors or disconnected. And some bright spark coming along and reconnecting the load CPC back to the pme at later date.

In summary - use the supplier earth that is excellent for 99.99% of the time or stick a brass spike in the ground and rely on an RCD for the off chance that the DNO lose the neutral only to your property while you are in the garden still wet and touching ...touching ...can’t think of what you would be that has a potential versus ground ?

 

[Ian1981]

You may roll your eyes and maybe every electrician on you tube does suggest/do this.
But that doesn’t make it a good idea necessarily. The regs suggest as “recommendation” in a PME supply to provide an earth electrode < 20 ohm for a swimming pool supply. But do a risk assessment- are there any exposed conductive parts liable to be touched by the user of hot tub (likely to be class 2) ? Is it an overhead supply /rural installation ? What is the likelihood of a lost neutral in the supply ? In the event of the lost pen conductor is the bonding to water and gas in place and reliable ?

Weigh up pros/cons of using the DNO earth and bonding any extraneous conductive parts (Using 3 core SWA, marshalling terminal if required) and having a Ze of 0.2 Ohm, having protection by ADS fault protection and additional protection via an RCD ...or isolating this excellent earth , having a variable earth rod Ra of 100 ohms plus in most cases and relying solely on an RCD to achieve fault protection disconnection time in 0.4s. A rod and connection that could be damaged outdoors or disconnected. And some bright spark coming along and reconnecting the load CPC back to the pme at later date.

In summary - use the supplier earth that is excellent for 99.99% of the time or stick a brass spike in the ground and rely on an RCD for the off chance that the DNO lose the neutral only to your property while you are in the garden still wet and touching ...touching ...can’t think of what you would be that has a potential versus ground ?

You do realise that was a tongue in cheek remark regarding most YouTube electricians who insist on installing electrodes as the only option because they all copy each other?

 

[Mark.fardon]

You do realise that was a tongue in cheek remark regarding most YouTube electricians who insist on installing electrodes as the only option because they all copy each other?

Ha no I didn’t I’m about 20 posts behind so didn’t get the context ?

 

[Ian1981]

Ha no I didn’t I’m about 20 posts behind so didn’t get the context ?

Ha no problem

 

[Mark.fardon]

So those that would install the rod your thoughts on the above risk assessment and preference for isolating the DNO earth and reliance on a long tent peg for safety from shock under normal conditions ?

 

[suffolkspark]

So those that would install the rod your thoughts on the above risk assessment and preference for isolating the DNO earth and reliance on a long tent peg for safety from shock under normal conditions ?

If the regs point towards using a long tent peg as you call it, then that's what gets used. I live in the countryside where most properties I work in are TT anyway

 

[Mark.fardon]

Well that makes sense of course

 

[davesparks]

The way I read the regs is its fine on pme if you can supplement it with a rod etc under 20ohm. I have recently achieved this on a couple of rods but dont often, so I always opt to seperate it off the pme

If you go back and read the regs again you will see that the >20ohm earth electrode is a note and that they do allow a hottub to be connected to a supply fed by PME without it.

 

[Ian1981]

I still don’t see the insistence of installing an electrode to an all insulated glorified paddling pool, so your In the water and step onto the grass??
Surely they would be included in part 7 if special supplementary requirements need to be considered ( I don’t consider them to fall into 702, if they did they’d be in there)

 

[suffolkspark]

If you go back and read the regs again you will see that the >20ohm earth electrode is a note and that they do allow a hottub to be connected to a supply fed by PME without it.

Ah I read it that it was a requirement but will have another look, just as an aside, the manufacturers of 3 out of the 4 I have installed in the last month have said they must have an electrode, 1 said the opposite. I'll look back in regs in a bit

 

[davesparks]

Ah I read it that it was a requirement but will have another look, just as an aside, the manufacturers of 3 out of the 4 I have installed in the last month have said they must have an electrode, 1 said the opposite. I'll look back in regs in a bit

I might be wrong, I haven't actually looked at it since the change to the 18th edition but it always used to be a note at the end of a regulation saying that you could install an earth electrode with Ra <20ohms connected to the equipotential bonding system of the installation.

A key point on this for me is that it says 'connected to the equipotential bonding system' not to create a seperate TT earthing system or anything like that. As far as I am concerned this means an earth electrode system connected to the MET of the installation.

 

[richy3333]

The regs suggest as “recommendation” in a PME supply to provide an earth electrode < 20 ohm for a swimming pool supply.

Which section of 702 - swimming pools and other basins are you quoting as I cant see this in my BBB?

 

[suffolkspark]

Our favourite word "reccomend" makes an appearance.....

 

[Ian1981]

Yes if you took recommend to mean shall, then we all would need to install AFDD’s in most installations, but that’s only a recommendation as well as I’ve not installed one yet!

 

[Mark.fardon]

If you go back and read the regs again you will see that the >20ohm earth electrode is a note and that they do allow a hottub to be connected to a supply fed by PME without it.

And the key here is if you can’t get 20ohms - which you won’t with an normal earth rod in majority of cases, then don’t install one .

Remember the regs are a guide not statutory .

 

[Ian1981]

And the key here is if you can’t get 20ohms - which you won’t with an normal earth rod in majority of cases, then don’t install one .

Remember the regs are a guide not statutory .

But part p a statutory document requires that the installation complies to bs7671 which gives a reason to follow it.

 

[Mark.fardon]

But part p a statutory document requires that the installation complies to bs7671 which gives a reason to follow it.

Really ? Where does it state that ?

 

[Ian1981]

Really ? Where does it state that ?

Here it’s an older copy mind
Should be designated and installed in accordance with bs7671.