PV installation - dedicated circuit, or from sub main board? MCS query

[vde-electrician]

hi
thank you for help in advance
have a potential pv installation for a garage roof that is some 60m from the main house (main incomer in the house).
Spoke to a napit/mcs worker - he said the pv installation has to be on a dedicated circuit. My interpretation is that a dedicated circuit on the garage
distribution board with an rcbo would be suffice. ie nothing else on the circuit apart from the pv - a new circuit. (a dedicated circuit?) He said that is not suffice and that a new
sub main from the house (off the meter tails) is the only way forward.....If all ac / dc isolators and labelling are in place, ie ac isolator at garage position and at the house position etc , then why is a new sub main needed?

This will obviously incur more cost and time for the customer

Are the instructions given accurate? Any help on this please.

thank you

 

[James]

The issues are based around disconnect times I believe.
on mains failure the solar inverter is allowed a time to stop generating

if the circuit is shared then it could prevent a circuit becoming dead in the required time.

a dedicated run back to main supply would mean you have not to worry about affecting any of the existing protection arrangements.

 

[plugsandsparks]

There are several ways to connect solar into an existing installation. I have used most of them, lol
Before i design the best approach, the size of the solar output, distance from the main house loads and any other relevant factors come into play. A new submain right back to the cutout is just one way, so not sure why your MCS guy is so insistent.

 

[vde-electrician]

There are several ways to connect solar into an existing installation. I have used most of them, lol
Before i design the best approach, the size of the solar output, distance from the main house loads and any other relevant factors come into play. A new submain right back to the cutout is just one way, so not sure why your MCS guy is so insistent.

a submain is the only way that meets regs. see mcs, MIS 3002 . other ways are non compliant. it states:

4.2:
In particular, attention is drawn to the unique combination of hazards associated with installation of PV systems highlighted in clause 1.3 of the above document. Furthermore an inverter supplied from a PV array must be connected via a dedicated circuit, to a spare fuseway in the main distribution unit, or to a fuseway in an additional dedicated distribution board.

 

[vde-electrician]

a submain is the only way that meets regs. see mcs, MIS 3002 . other ways are non compliant. it states:

4.2:
In particular, attention is drawn to the unique combination of hazards associated with installation of PV systems highlighted in clause 1.3 of the above document. Furthermore an inverter supplied from a PV array must be connected via a dedicated circuit, to a spare fuseway in the main distribution unit, or to a fuseway in an additional dedicated distribution board.

so in theory if your mains house db is fed from a swtich fuse at your meter, the main house db is no longer dedicated and thus you can't have a pv installed from it. So there are lots of non compliant installations if this is the case?

 

[plugsandsparks]

There are many more installation types where issues would arise, BTW can you screenshot the document you are referring to as my copy of MIS 3002 does not say that (as far as i can read

 

[vde-electrician]

There are many more installation types where issues would arise, BTW can you screenshot the document you are referring to as my copy of MIS 3002 does not say that (as far as i can read

hi, page 7 of 14 , issue 1.4 mis 3002 . perhaps i'm looking at an older version. i'll have to double check

 

[plugsandsparks]

Current issue is 4 and after November its issue 5.
I do see many commercial installations done by a number of companies (as i do the EICRs) and roughly 50% go to the main DB with the rest hooking into a sub board off the main DB. Not seen anything in BS7671 that would alarm me of such "problems" - so have not coded these installs.....

 

[vde-electrician]

Current issue is 4 and after November its issue 5.
I do see many commercial installations done by a number of companies (as i do the EICRs) and roughly 50% go to the main DB with the rest hooking into a sub board off the main DB. Not seen anything in BS7671 that would alarm me of such "problems" - so have not coded these installs.....

so you have taken pv supply off sub boards?

 

[timhoward]

so you have taken pv supply off sub boards?

It's not really as simple as "you can do it" or "no you can't".
PV downstream from any upstream shared RCD is a no-no.
PV on a shared final circuit is a no-no.
In both cases designed disconnected times cannot be guaranteed as the inverter will back-feed after a trip until it shuts itself down, which may take > 1 second.

But that's not to say it can't be done, IF the installer understands these issues and has checked they are non-issues.