I would like some advice on PV wiring. Currently I don't have a PV setup but I am working on a solution to first get wiring from my roof to the garage before I get an installer to do the rest.

There is no direct path from my top floor to the garage. The only access point is the plumbing shaft that houses all the PVC pipes for the waste water and solid stuff. The shaft runs from my garage roof space to the top floor roof space and is totally enclosed (no access from outside except from within the roof cavities).

Here is my plan: I want to install a 8-way DB in the top floor roof space and make provision for 2 x DEHN FM surge protectors. This DB will have 8 x panel mount MC4 connectors to connect two separate strings to the garage roof. Only one will currently be used but for expansion I have the option of another separate feed. The surge protection has additional 'status' contacts that I can connect to a monitoring system to see if they are Ok or not.

The next step is to put another 8-way DB in the garage roof without any components, just the same 8 x MC4 panel mount connectors and bridge them internally from In to Out to form a termination DB.

In the 'poop-shaft' as I call it, I run 2 x 25mm PVC pipes each with 2 x 6mm PV cable in each and one with an additional earth cable that terminates between the two DB's. Sort-off like structured wiring in the Networking/Datacentre environments. When I am ready to install my panels I then run the panels to the top floor DB and then just a small stretch from the Garage DB to the Solar Inverter. The idea is not to ever fiddle with cabling in the 'poop-shaft' as there is NO space and I am getting older so don't really want to get in there if it can be avoided. If not used, the second pair of cabling also acts as a backup so I can switch over if there ever is damage to the first pair.

The current planned PV design is an AC coupled Fronius inverter running +-3.5KW @ +-500V odd. The MC4 connectors are well withing spec current wise. 6mm cable is because of the distance and future capacity growth.

So the question: Do the clever guys agree with this plan? I could sacrifice the Garage Roof DB and go straight to the DB next to the Fronius Inverter but then the cable has to flow through a few more angles via the PVC conduit to get there. All possible of course.

42 minutes ago, Ingo said:

I could sacrifice the Garage Roof DB and go straight to the DB next to the Fronius Inverter but then the cable has to flow through a few more angles via the PVC conduit to get there. All possible of course.

I would install 1 single  DB, every joint or connection is a potential failure point as well as you increase the losses. Straight from the roof to the box next to the inverter, Have your Surge arrestors as well as Isolator and fuses, all in one easy accessible place. Less losses and easier to monitor and maintain. 

Thanks for the wisdom @Jaco de Jongh. I will do the PVC conduits then and leave them open-ended where the installer can better access the entry points. Being right in the corner of the roof and wall is going to be difficult enough even with the conduits already in place.

1 hour ago, Ingo said:

a few more angles via the PVC conduit to get there

One way to deal with bends and pulling cable, is put the cable in while gluing the PVC together. Saves you the effort of doing it later, especially if you don't have a good fisher tape around.

3 hours ago, Ingo said:

I will do the PVC conduits then and leave them open-ended where the installer can better access the entry points.

You can also install a steel draw wire with the pipe, The installer can then secure his wires to it and just pull the wires through. And old practice used by many construction electricians. 

13 hours ago, Jaco de Jongh said:

You can also install a steel draw wire with the pipe, The installer can then secure his wires to it and just pull the wires through. And old practice used by many construction electricians. 

In my first house, they installed an empty conduit with such a steel wire in the one corner, running from the roof space down to the ground floor. Such foresight is almost rare these days... 🙂

We used it some years later to draw in an ethernet cable between the floors. And then another year or so later, we stuck the security system's cables through the same conduit. It had saved me major wiring issues twice...

And don't forget an extra wire to earth the panels properly. PITA if you have to do it afterwards, so an extra conduit for that. Earth wire go strait to earthing point, and not via inverter location. Is that thinking right?