Commercial Pv Ac Connection

Please see the attached image. This is a fairlly big place. The main incomer and a big dist panel are right down the other end of building. A Panel (amomgst other things) near Reception is fed from Main panel. From this panel is a dist circuit feeding another building (Annex). There are 2 4 core SWA's to this building. The one i'm interested in is the one feeding the 'Power' CU and is fed in 35mm 4C. the other is Lighting and the SWA is slightly smaller, Maybe 25mm 4C but no marking on this cable that I can see.

I hear conflicting views on the Volt Drop allowed on PV. Way back when I did my qual I was told 1%. Later I was told 1% is only for DC All in 2%. Also read 3% all in. Anyways, DC Loss is minimal so worst case sticking to 1% allows up to about 60m on a 35mm 4C SWA from inverters (well a small DB at side).

The bit that is confusing me is: where do I consider the VD to?

• The Connection point. i.e the Annex DB
• All the way back to the Incomer?

The Ultimate question is: Can I connect this PV system to the Annex DB?

Answers on a postcard

p.s. I was told also that there is a backup Genny for the place but could not access it as the caretaker had the keys and wasn't on site. How does this affect (if at all) PV systems?

Feel a bit of a noob but I'm not really a commercial guy. Will have a crack at owt though.........

I work on 1% upto the generation meter/ sub board, ideally it should be back to main incomer, but as much of the leccy being generated sounds like it will used at the sub-board, then I don't worry too much as long as the sub-main is man enough to take the total back-feed should the PV be generating and power ccts not be in use. The inverters output balanced 3 phase so sizing the neutral for total back feed is not required.

binky said:

I work on 1% upto the generation meter/ sub board, ideally it should be back to main incomer, but as much of the leccy being generated sounds like it will used at the sub-board, then I don't worry too much as long as the sub-main is man enough to take the total back-feed should the PV be generating and power ccts not be in use. The inverters output balanced 3 phase so sizing the neutral for total back feed is not required.

Click to expand...

Sound mate, That was going to be my theory. The sub DB can take it, 100 Main switch, spare 3p way, etc. Fed from 100A MCB. So within limits.

Based on this theory I should be ok then. I guess at a push I could put 2 inverters to this DB and then the 3rd to the lighting DB which is same type of DB fed with what seems to be 25mm 4C from and 63A MCB. I would like to keep them together if poss for integrity sake (OCD) lol

Thanks buddy and thanks again for today....