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

[Scottishlad123]

Hi there,

I have been asked to install a 32a supply for a hot tub for a client. I haven’t installed a supply for a hot tub before and having done a bit of research I am getting mixed answers about doing this on a PME system. I have a DB under the stairs with plenty of spare ways so I would be planning to take a 6mm armour from here outside to a rotary isolator. what I am unsure about is the earthing scenario, I have seen a lot of people saying this will require an earth rod. There is also the possibility of taking tails directly of the Henley blocks into a small garage unit and feeding the hot tub of its own DB. Any help is greatly appreciated thanks in advance.

 

[davesparks]

Being brutely honest, I have no clue, whichever references exporting PME.

A quick Google search brings up;

Domestic EV Installations

use the matt:e EV connection units to make EV charge point installs simpler

matt-e.co.uk

There is no regulation which references exporting PME because there is no such thing as exporting PME.

You won't find a regulation to support your statement because none exists.

As per your link those units are intended to protect EV charging points and the regulations do specifically allow such protection to be used for EV charging points.

Nothing in the regulations allows these devices to be used in any other situation where PME is not permitted to be used.

 

[Lister1987]

There is no regulation which references exporting PME because there is no such thing as exporting PME.

You won't find a regulation to support your statement because none exists.

As per your link those units are intended to protect EV charging points and the regulations do specifically allow such protection to be used for EV charging points.

Nothing in the regulations allows these devices to be used in any other situation where PME is not permitted to be used.

Rightly or wrongly I've seen a few YT sparks use the matt-e for hot tub installs a opposed to EV chargers, my impression was they were using them to avoid putting in an earth rod and making use of the existing PME arrangement, in a fashion, I base my loose and likely faulty understanding on that

 

[davesparks]

Rightly or wrongly I've seen a few YT sparks use the matt-e for hot tub installs a opposed to EV chargers, my impression was they were using them to avoid putting in an earth rod and making use of the existing PME arrangement, in a fashion, I base my loose and likely faulty understanding on that

I suspect they are using them due to a lack of knowledge, or due to the manufacturers of the device paying them to use them.
It could also be down to one of them doing it for these reasons and the rest just following like sheep.

Remember there is nothing regulating the technical accuracy of the content on YouTube,
There was recently a video published somewhere online where an American demonstrated making 'English tea' that used a microwave and came out looking like a mug of dishwater, it's on the Internet but that doesn't make it right!

You would do far better to get your information from trusted, provably reliable sources.

This subject kind of puts me in mind of D.W. Cockburn's book on earthing and bonding, it was published by a major publisher but completely and utterly wrong/dangerous

 

[marcuswareham]

Rightly or wrongly I've seen a few YT sparks use the matt-e for hot tub installs a opposed to EV chargers, my impression was they were using them to avoid putting in an earth rod and making use of the existing PME arrangement, in a fashion, I base my loose and likely faulty understanding on that

In my opinion using the Matt-e single phase verison for a hot tub gives you a false sense of security, as it only protects against some PEN conductor faults but not all, it is likely you can have a open PEN conductor and still have a voltage between 207v-253v between L - N depending how the phases are balanced and where the break is, Matt-e themselves even demonstrate this on there 3 phase o-pen video

Although this does mitigate do a degree and perhaps the likelihood of a PEN fault is small. The effects of a fault can be fatal

e.g. PME supply with plastic supply pipes and therefore no extraneous conductive parts water heating element bonded to CPC and in contact with the hot tub water, if the hot tub is placed on grass/soil and you step out and simultaneously in contact with true earth and the water (effectively connected to the PME earth during a fault) then there could be a dangerous voltage between the water and true earth (and you are also wet)

I don't know how using a matt-e would fit within the regs, but as others have suggested swimming pools is the closest/same thing

 

[Lister1987]

I suspect they are using them due to a lack of knowledge, or due to the manufacturers of the device paying them to use them.
It could also be down to one of them doing it for these reasons and the rest just following like sheep.

Remember there is nothing regulating the technical accuracy of the content on YouTube,
There was recently a video published somewhere online where an American demonstrated making 'English tea' that used a microwave and came out looking like a mug of dishwater, it's on the Internet but that doesn't make it right!

You would do far better to get your information from trusted, provably reliable sources.

This subject kind of puts me in mind of D.W. Cockburn's book on earthing and bonding, it was published by a major publisher but completely and utterly wrong/dangerous

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

 

[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.