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!