Where can a PV array be connected?

I suspect that a PV array would normally be connected between the meter and the first DB, but can it be connected more peripherally please?

The most suitable area of roof is at the opposite end of the premises from the electrical origin. However, there is a small DB with spare ways adjacent to the loft space. It supplies one lighting and one socket circuit and is seldom significantly loaded. The distribution circuit from the main DB is 16 mm² singles (with the live conductors being sheathed). As far as I can see, it travels through under-floor voids and is boxed in with other services as it ascends in a bathroom so RCD protection is not required. If the inverter can be situated in the loft space then only a short length of AC cable would be required.

This is what I have in mind.

Parents
  • In principle the AC side of the invert can be (and often is) connected to DBs hanging off submains. The inverter will need to be on its own circuit from the DB (not sharing a final circuit with any current-using equipment) - so isolation (either by CU MCB or local rotary isolator) usually isn't an issue.

    Overload protection needs some thought since some conductors (and switchgear) will potentially be fed from two sources - so the ordinary upstream (from a grid perspective) overcurrent protective devices don't necessarily provide adequate protection any more. E.g. a 100A rated DB which can also perhaps source 16A from the inverter won't any longer be protected from overload by the 100A DNO fuse (or the submain OPD) - and that's likely to be the case whether the PV is connected though an existing DB or a new dedicated one. Where the PV output can be consumed on-site there's also the issue that in terms of heat dissipation from MCBs etc the 16A (or whatever) from the PV has to be counted twice - once from it's own MCB and again as the current goes out again via one of the other circuits - all in addition to the 100A (say) from the grid. Having the PV connected to a lightly loaded CU with an grid-side overcurrent protective device significantly lower than the DB's rating, if anything is likely to help considerably with these problems.

      -  Andy.

Reply
  • In principle the AC side of the invert can be (and often is) connected to DBs hanging off submains. The inverter will need to be on its own circuit from the DB (not sharing a final circuit with any current-using equipment) - so isolation (either by CU MCB or local rotary isolator) usually isn't an issue.

    Overload protection needs some thought since some conductors (and switchgear) will potentially be fed from two sources - so the ordinary upstream (from a grid perspective) overcurrent protective devices don't necessarily provide adequate protection any more. E.g. a 100A rated DB which can also perhaps source 16A from the inverter won't any longer be protected from overload by the 100A DNO fuse (or the submain OPD) - and that's likely to be the case whether the PV is connected though an existing DB or a new dedicated one. Where the PV output can be consumed on-site there's also the issue that in terms of heat dissipation from MCBs etc the 16A (or whatever) from the PV has to be counted twice - once from it's own MCB and again as the current goes out again via one of the other circuits - all in addition to the 100A (say) from the grid. Having the PV connected to a lightly loaded CU with an grid-side overcurrent protective device significantly lower than the DB's rating, if anything is likely to help considerably with these problems.

      -  Andy.

Children