Where can I take supply from?

[MBE Contracting]

Is it possible to take my supply from a 60 amp 3 phase sub board to feed a 38kwp pv system rather than have to go right back to the origin of the supply? I thought you were able to do that but I have recently come across some conflicting reports.

 

[BruceB]

Yes in principle it is possible providing amongst other things the PV is on its own circuit from the sub-board. Is there a particular issue you have in mind? The existing sub-main may not be sized for the voltage drop you will be designing for.

 

[MBE Contracting]

Yes in principle it is possible providing amongst other things the PV is on its own circuit from the sub-board. Is there a particular issue you have in mind? The existing sub-main may not be sized for the voltage drop you will be designing for.

Hi Bruce, I have run the submain design through my SMA design software and it is showing I am below the volt drop parameter, it was just that a rival contractor quoting for the job had told the customer that you have to take the feed from the origin of supply and I was wondering if there has been any recent guidance from the MCS on the subject.

 

[BruceB]

Certainly nothing specific from MCS, they say follow the PV Guide. Page 44 onwards in the PV Guide has the requirements. Must be on its own final circuit. No reason in my opinion that cannot be from a sub-board, provided the normal design criteria are met.

There may be good electrical reasons to go from the origin as the G59 the voltage limits you are working to are stricter than G83, but do the design, including measuring local voltages and supply impedance and you should be able to judge whether using existing wiring is adequate.

There may also be good commercial reasons to go from the origin, as it keeps your work completely separate from existing client installation, which might be helpful if there are faults that need tracking down or if it is claimed the PV is causing problems later. That is a judgement call.

 

[MBE Contracting]

Certainly nothing specific from MCS, they say follow the PV Guide. Page 44 onwards in the PV Guide has the requirements. Must be on its own final circuit. No reason in my opinion that cannot be from a sub-board, provided the normal design criteria are met.

There may be good electrical reasons to go from the origin as the G59 the voltage limits you are working to are stricter than G83, but do the design, including measuring local voltages and supply impedance and you should be able to judge whether using existing wiring is adequate.

There may also be good commercial reasons to go from the origin, as it keeps your work completely separate from existing client installation, which might be helpful if there are faults that need tracking down or if it is claimed the PV is causing problems later. That is a judgement call.

Thanks Bruce, pretty much as I was thinking, also just spoke to DNO and they couldn't see any problems as long as usual criteria has been met. I'd like to here from an installer of larger systems though just to get some more feeling of possible issues relating directly to subject.

 

[jason121]

I have installed several 40kw and 50kw installations from sub mains supplies. Some times its impracticable to run cables long distances through buildings. No problems yet with them. I even have my own large scale installation on 3 different buildings all connected to sub mains in the same yard with three different generation meters . Forth meter going in in a couple of weeks to add to system.

 

[Gavin A]

Hi Bruce, I have run the submain design through my SMA design software and it is showing I am below the volt drop parameter, it was just that a rival contractor quoting for the job had told the customer that you have to take the feed from the origin of supply and I was wondering if there has been any recent guidance from the MCS on the subject.

the other lot are talking a load of rubbish, ask the customer if they'd prefer to pay for your expertise, or their unnecessary cable run.