Another Hot tub install

[pc1966]

In real terms how often does a PME fault occur? I have never experienced or seen one.

I have heard around 300-350 per year.

 

[Mike Johnson]

Heard about is not experiencing them, how many in your time as an Electrician have you actually had to deal with one?

 

[ipf]

Somehow, I think, if it were a seriously regular occurrence, the supply authorities might be under a great deal of pressure to 'get it sorted'.
It is, after all, their duty.
In all fairness, every supply earthing problem I've reported has resulted in a same day visit.

 

[Mike Johnson]

All true, but I was trying to get to the bottom of how many Electricians on this Forum have had first hand experience of a PME fault, personally I have never found or had to deal with one!

 

[HappyHippyDad]

All true, but I was trying to get to the bottom of how many Electricians on this Forum have had first hand experience of a PME fault, personally I have never found or had to deal with one!

I think even if @pc1966 had said he had never come across a PEN break that would not really mean they do not exist. It would neither suggest they were common or rare. You would need to ask perhaps 1000 electricians across varying locations, then perhaps you could form a statistical judgement.... but not on a population of 1.
Why not start a poll, it would be interesting.

 

[pc1966]

I started a thread about this sort of thing here:

Open PEN causes?

The risks related to an open PEN in TN-C-S are often discussed here, say in relation to external supplies to out buildings, etc, but I wondered what is the main reason(s) for an open PEN fault? I assume it is something to do with bad jointing techniques as with concentric cables it would be...

www.electriciansforums.net

From the comments there it seems to be related to water ingress in joints in aluminium waveform cables, etc, so how likely you are to see it would depend on you being in a region with old-ish TN-C-S supplies. It does make the news occasionally when someone gets hurt:

Burnley primary school pupils suffer electric shocks

Ten children and a teacher suffer electric shocks at a Lancashire primary school.

www.bbc.com

 

[Mike Johnson]

I think even if @pc1966 had said he had never come across a PEN break that would not really mean they do not exist. It would neither suggest they were common or rare. You would need to ask perhaps 1000 electricians across varying locations, then perhaps you could form a statistical judgement.... but not on a population of 1.
Why not start a poll, it would be interesting.

I never suggested they did not exist and asked the question of how many Electricians on here have experienced a PEN break, I did not ask a population of 1.

 

[Gazthesparky]

So are we now reached the conclusion that I should isolate the PME supply on the hot tub supply and the socket and TT the 2 supplies. Keeping the house PME

my next issue I have is that the customeris wanting an extra consumer unit put in so they can add a hob in the future if I TT my new one there will be 2 earthing systems in the property.

Should I then install 2 consumer units one for the hot tub supply/socket (TT) and one for the future hob PME

means buying 2 units and 2SPDs

or installing 1 new unit and running PME sub main to hot tub and isolating the earth and installing an Earth rod at the hot tub
Only issue with that is how to Earth the socket too the same Rod

 

[Midwest]

Where is the hot tub being installed, in a structure, on a deck, grass or soil or stone?

 

[pc1966]

So are we now reached the conclusion that I should isolate the PME supply on the hot tub supply and the socket and TT the 2 supplies. Keeping the house PME

my next issue I have is that the customer is wanting an extra consumer unit put in so they can add a hob in the future if I TT my new one there will be 2 earthing systems in the property.

Should I then install 2 consumer units one for the hot tub supply/socket (TT) and one for the future hob PME

means buying 2 units and 2SPDs

or installing 1 new unit and running PME sub main to hot tub and isolating the earth and installing an Earth rod at the hot tub
Only issue with that is how to Earth the socket too the same Rod

If the proposed CU change is likely to happen before the hot tub installation you are best simply to put in one big enough CU for the lot and keep the house on PME. Single SPD, single isolation switch, everything consistent.

If you can run SWA out to the hot tub you have the option to simply feed it from a MCB and put the RCD out there in an IP65 or similar enclosure (as for caravan feed, etc) and have all that is down-stream of the RCD on a local TT earth rod.

Or if it is easier and your CU choice has DP RCBO then all you need at the hot tub end is the isolator and to separate the SWA earth (from the PME supply) from the outdoor circuits' TT earth. So use a plastic gland, etc, and not the usual metal type for connecting the armour up.

If the sockets are not expected to be used for large loads or extended in the future, then just put them on the same 32A supply as the hot tub. That way you don't risk a PME-derived earth to a lamp or similar being next to a good true-Earth TT supply.

Others might have some better ideas!

 

[Gazthesparky]

If the proposed CU change is likely to happen before the hot tub installation you are best simply to put in one big enough CU for the lot and keep the house on PME. Single SPD, single isolation switch, everything consistent.

If you can run SWA out to the hot tub you have the option to simply feed it from a MCB and put the RCD out there in an IP65 or similar enclosure (as for caravan feed, etc) and have all that is down-stream of the RCD on a local TT earth rod.

Or if it is easier and your CU choice has DP RCBO then all you need at the hot tub end is the isolator and to separate the SWA earth (from the PME supply) from the outdoor circuits' TT earth. So use a plastic gland, etc, and not the usual metal type for connecting the armour up.

If the sockets are not expected to be used for large loads or extended in the future, then just put them on the same 32A supply as the hot tub. That way you don't risk a PME-derived earth to a lamp or similar being next to a good true-Earth TT supply.

Others might have some better ideas!

The customer is just wanting an additional consumer unit fitting. There is an isolator on the meter tails so I was planning on henley blocking the tails and installing the new consumer unit. this gives 1 isolation point to the property.

so going the TT way at the hot tub if I take the the supply down to the isolator with the PME connected is it just a normal stuffing gland used and the armour cut back ? or is there a special plastic gland made for this situation ?

The double socket they have asked for it to be able to be switched from inside the house. so I was going to run a separate 2.5mm SWA for the socket but again its difficult to earth rod it and keep the PME separate.

I had planned to use a 3 core SWA for the hot tub as originally I was going to transport the PME. But could just change this to 2 core. If however I keep the 3 core and use the 3rd core as a switched feed for the socket. I have a 4 pole rotary isolator I can take it through that so switching the hot tub off isolates the lot. Then just take a loop a 4mm SWA from the isolator to the socket using the TT earth and a shared neutral.

Inside the house fit the new consumer and double pole RCBO feed the Hot tub supply and also a supply to a 20amp DP switch from that RCBO so it keeps it all on the one supply. then join the DP switch switched supply onto the 3rd core of the swa.

originally I had planned to run a separate 2.5mm SWA back to the house but this then means id have a PME earth near the hot tub.

the socket and Hot tub supply are in separate areas as the isolator is 2 meters from the TUB and I want the socket to be at least 3 meters away.

 

[pc1966]

The customer is just wanting an additional consumer unit fitting. There is an isolator on the meter tails so I was planning on henley blocking the tails and installing the new consumer unit. this gives 1 isolation point to the property.

OK, makes sense.

so going the TT way at the hot tub if I take the the supply down to the isolator with the PME connected is it just a normal stuffing gland used and the armour cut back ? or is there a special plastic gland made for this situation ?

No, just the usual IP68 things you get most places.

If you want a neat cover for the armour then some glue-lined heatshrink sleeving is great.

The double socket they have asked for it to be able to be switched from inside the house. so I was going to run a separate 2.5mm SWA for the socket but again its difficult to earth rod it and keep the PME separate.

I had planned to use a 3 core SWA for the hot tub as originally I was going to transport the PME. But could just change this to 2 core. If however I keep the 3 core and use the 3rd core as a switched feed for the socket. I have a 4 pole rotary isolator I can take it

No, that sounds a bad idea and is basically a borrowed neutral!

Do they really need to isolate the sockets and have the hot-tub switched on?

A simpler and safer option is to run tub & sockets from the same supply and just put indoors a 32A or higher cooker-style DP switch so they can switch it on and off easily. Ideally one with a neon to show it is powered.

 

[Gazthesparky]

OK, makes sense.


No, just the usual IP68 things you get most places.

If you want a neat cover for the armour then some glue-lined heatshrink sleeving is great.


No, that sounds a bad idea and is basically a borrowed neutral!

Do they really need to isolate the sockets and have the hot-tub switched on?

A simpler and safer option is to run tub & sockets from the same supply and just put indoors a 32A or higher cooker-style DP switch so they can switch it on and off easily. Ideally one with a neon to show it is powered.

I get that but unfortunately the hot tub supply needs to be on 24/7 and the switches socket.

I don’t think there would be a borrowed neutral as such. The tub supply would be fed directly from the RCBO and the socket switch inside the house would be supplied from the same RCBO to a DP isolator switch then that switched live would be the 3rd core of the armour

so the armour would have Live Neutral and switched live for the socket.

at the tub end there would be a 4 pole 40 amp isolator which would isolate all of the supply.

I woulD put a rod at the 40amp isolator and TT from there after insulating the PME in a gland

the socket would be fed via the 3rd core (Switched live)and taking it’s neutral from the isolator neutral and the earth from the Rod

I don’t think it would cause an imbalance for the RCBO as the supply to the circuit is coming from the same RCBO

 

[pc1966]

I get that but unfortunately the hot tub supply needs to be on 24/7 and the switches socket.

Ah, OK that makes sense if its running to keep water hot/clean long-term.

I don’t think there would be a borrowed neutral as such. The tub supply would be fed directly from the RCBO and the socket switch inside the house would be supplied from the same RCBO to a DP isolator switch then that switched live would be the 3rd core of the armour

so the armour would have Live Neutral and switched live for the socket.

OK, that makes sense.

I don’t think it would cause an imbalance for the RCBO as the supply to the circuit is coming from the same RCBO

Should be fine as they have same live/neutral paths, so unless something very leaky is connected it should be balanced.

 

[Midwest]

the socket would be fed via the 3rd core (Switched live)and taking it’s neutral from the isolator neutral and the earth from the Rod

I don’t think it would cause an imbalance for the RCBO as the supply to the circuit is coming from the same RCBO

That doesn't sound right to me, I can't think why? Plus you still haven't answered my question as to where the hot tub would be situated.
[automerge]1597940892[/automerge]
I've trawled back through some older threads on this subject, and found this recent one;

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

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...

www.electriciansforums.net

Still not convinced of the need to TT the supply, with the appropriate placement of said hot tub.

 

[Gazthesparky]

That doesn't sound right to me, I can't think why? Plus you still haven't answered my question as to where the hot tub would be situated.

Not sure what you are getting at ?? at the bottom of the customers garden
[automerge]1597940892[/automerge]
I've trawled back through some older threads on this subject, and found this recent one;

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

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...

www.electriciansforums.net

Still not convinced of the need to TT the supply, with the appropriate placement of said hot tub.
[/QUOTE]

 

[Midwest]

Not sure what you are getting at ?? at the bottom of the customers garden
[automerge]1597940892[/automerge]
I've trawled back through some older threads on this subject, and found this recent one;

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

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...

www.electriciansforums.net

Still not convinced of the need to TT the supply, with the appropriate placement of said hot tub.

Would you have the same concerns, if the hot tub was in the house? Bit like ev chargers, where the car is being charged in garage.

Is the hot tub sat on the grass, or in some sort of structure, is all I’m asking.

 

[Gazthesparky]

Would you have the same concerns, if the hot tub was in the house? Bit like ev chargers, where the car is being charged in garage.

Ah I see what you are getting at now lol

Is the hot tub sat on the grass, or in some sort of structure, is all I’m asking.

Its sat on a concrete patio that has been laid to support the hot tub. With a lawn around it so if we are assessing the location Im guessing that if its on a patio of some description you could say that the person is insulated in some sense from the true earth of the soil. So there wouldn't be or a very poor earth path from the hot tub to the rod.

 

[pc1966]

I don’t think there would be a borrowed neutral as such. The tub supply would be fed directly from the RCBO and the socket switch inside the house would be supplied from the same RCBO to a DP isolator switch then that switched live would be the 3rd core of the armour

Just wondering about this. To me the hot tub supply should have an inside switch as well (so if they are away they don't need to padlock the external isolator to prevent somebody messing around with it, etc).

You mention the DP isolator, and later you mention a 4-pole rotary isolator outside. Do you mean what I think you do (and would suggest myself) where you have:

RCBO => indoor DP switch (for hot tub & sockets, normally on for tub) =>
DP live => feeds SWA "permanent live"
DP live => indoor SP switch (for sockets only, normally off) => feeds SWA "switched live"
DP neutral => feeds SWA neutral

SWA => outdoor 4-pole rotary isolator (for hot tub & sockets) =>
pole 1 = switched live to sockets
pole 2 = neutral to sockets
pole 3 = permanent live to hot tub
pole 4 = neutral to hot tub

So when the outdoor isolator is off you can IT test the sockets independently of the hot but supply, etc.