This may raise an eyebrow or two...

[Dyslexicbloke]

Hi folks,
I have a hydro customer who also owns a fish farm. Currently, he has 3 entirely separate TN-CS supplies, the hydro which is 3 phase and fine, the fish farm which is nasty and single phase and the house and workshop, also single phase, which is marginally better but not good in many respects.

The plan is, at the moment, to ditch fish farm and house supplies and put everything on the hydro.
I am aware that this will require distribution upgrades because both systems will essentially be new installations when reconnected, at least I am assuming that would be the case, and we will likely use a local electrical contractor to do the work, once it is specked.

Distribution to what will considered sub boards now is organised and we have speced RCD protection for both cables. We have had to use adjustable MCCB's to get disconnection time right but the design look good... Not that anyone has signed off on it yet.

However The customer is now talking about keeping the existing domestic supply as a backup and wants a changeover switch...
This presents some issues to say the least.
The connection heads are about 160m apart which means we cant link P-N at that location as iot is well inside the installation.
However to use the existing TN-CS connection at that point we would of course be doing exactly that because the link is in the DNO head.

My first thought was a 5 pole changeover so that the P&N are handled separately. I dint have a copy of the 18th/2 right now and although I know that PE switching can be done I suspect the regs will have some pretty stiff requirements for implementing that. I encounter switched P-N links quite a bit as I work on hydro systems that are essentially operating islanded when starting up but I don't think I have ever seen The source of the PE switched.

Comments would be welcome but 63A 5 or 6 pole changeover switches seem to be a rare beast, at least if we want a 'real' one' which of course is not negotiable.

That raises the question... Could we put the entire house on a plug? Yes I know, but 63A 5 pin plugs will accept a 16mm SY and if both supplies were brought to interlocked socket isolators it wouldn't be possible to connect or disconnect under load and the separation of both P & N of both systems would be total and guaranteed.

Please note this post is here because I recognise this is a tad unusual and have no realistic way to check if it is even a valid approach, let alone dig into the detail.
Any and all comments will be very much appreciated.

Thanks for looking,
Al

 

[mort2376]

From a tax point of view I hope he is installing meters at all points as if he's found out that the business is paying his house electrics then they will fine him and scrutinise his accounts with a fine tooth comb.

 

[Murdoch]

Are you familiar with the implications of part P in Wales

 

[Dyslexicbloke]

Are you familiar with the implications of part P in Wales

No, at least not yet. I am also nor designing or signing stuff off either, at least not up to this point. Generally I will explain what is required functionally and somone else will check that and do the testing.
This may change once I am back up to speed but I suspect there is a great deal more to deal with over and above Part P

Is there something speciffic about part P that I should know that relates to this question. BTW the job in question is in Scotland which I believe is not the same. I would still like to know mind you.

MID approved meters on all sub services, yes.

 

[binky]

part P doesn't apply to Scotland.

 

[binky]

Hi folks,
I have a hydro customer who also owns a fish farm. Currently, he has 3 entirely separate TN-CS supplies, the hydro which is 3 phase and fine, the fish farm which is nasty and single phase and the house and workshop, also single phase, which is marginally better but not good in many respects.

The plan is, at the moment, to ditch fish farm and house supplies and put everything on the hydro.
I am aware that this will require distribution upgrades because both systems will essentially be new installations when reconnected, at least I am assuming that would be the case, and we will likely use a local electrical contractor to do the work, once it is specked.

Distribution to what will considered sub boards now is organised and we have speced RCD protection for both cables. We have had to use adjustable MCCB's to get disconnection time right but the design look good... Not that anyone has signed off on it yet.

However The customer is now talking about keeping the existing domestic supply as a backup and wants a changeover switch...
This presents some issues to say the least.
The connection heads are about 160m apart which means we cant link P-N at that location as iot is well inside the installation.
However to use the existing TN-CS connection at that point we would of course be doing exactly that because the link is in the DNO head.

My first thought was a 5 pole changeover so that the P&N are handled separately. I dint have a copy of the 18th/2 right now and although I know that PE switching can be done I suspect the regs will have some pretty stiff requirements for implementing that. I encounter switched P-N links quite a bit as I work on hydro systems that are essentially operating islanded when starting up but I don't think I have ever seen The source of the PE switched.

Comments would be welcome but 63A 5 or 6 pole changeover switches seem to be a rare beast, at least if we want a 'real' one' which of course is not negotiable.

That raises the question... Could we put the entire house on a plug? Yes I know, but 63A 5 pin plugs will accept a 16mm SY and if both supplies were brought to interlocked socket isolators it wouldn't be possible to connect or disconnect under load and the separation of both P & N of both systems would be total and guaranteed.

Please note this post is here because I recognise this is a tad unusual and have no realistic way to check if it is even a valid approach, let alone dig into the detail.
Any and all comments will be very much appreciated.

Thanks for looking,
Al

Not quite sure what to suggest, but with TNC-s it's considered bad form to 'export the earth' ( I'm sure someone will correct that term) outside of an exponential zone, ie one building. So I would be inclined to earth house and fish farm via earth rods ie convert to TT system.

Sub mains also dont need RCD protection - no harm in having it but not a requirement.

Sounds like an awful project either way