FYI: mixing MC4 solar panel connector brands

[Siwastaja]

When our house was built 20 years ago I ran two additional runs of TPS cable (2.5mm 2Core&Earth) between the attic space and the main distribution board....
So I want to use these cables to connect two strings of PV panels on the roof to a grid tied inverter to be installed adjacent to the distribution board.

Most likely illegal and possibly dangerous. PV string cabling is a special type because it is un-fused HVDC with can sustain a significant arcing which never breaks because of lack of zero crossing in voltage, and lack of fusing. Consequence of short-circuit in normal house AC wiring is a blown fuse; consequence of short-circuit in PV DC wiring is a definite house fire, that's why the requirements for the cabling and their insulation, specificially against mechanical stress, are higher.

Of course in practical world it is still very unlikely to burn your house down. Just that the risk is there, and the risk is statistically high enough that such installs are not allowed in large numbers. (Small number of illegal installs then work "by luck".)

Professional installers, which you obviously should use, are usually quite good in finding low-effort routes for the cabling, including optimum place for the inverter. A decent hammer drill makes a 16mm hole on a thick concrete in less than a minute.

[nctnico]

Agreed. A good approach is to keep + and - wires strictly seperated using (flexible) conduits (one for each wire color) so that even when the insulation gets compromised, the chances of arcing are next to non existent. For the install I did, the supplier sold me 1000V rated 4mm^2 wires which have two layers of insulation; these are specific wires for use in solar panel installations as the outer insulation also needs to be UV resistant.

As Siwastaja noted solar panel installers can be creative in finding solutions but these might not be the most aesthetically pleasing ones. For example: one of my neighbours has a rectangular piece of indoor wire trunking running across the front of their home. Ugly as hell. Also make sure the wiring between the inverter and distribution panel can handle full power of the inverter. I spend several days on getting this job done in a way the wiring is out of sight (going from ground floor to the attic where the inverter is). I had to drill large (25mm / 30mm) holes through (in total) a meter of prefabricated, steel re-inforced concrete. Although I will admit this project got a bit out of hand due to unforeseen obstacles.

[fastbike]

Agreed. A good approach is to keep + and - wires strictly seperated using (flexible) conduits (one for each wire color)
...
I had to drill large (25mm / 30mm) holes through (in total) a meter of prefabricated, steel re-inforced concrete. Although I will admit this project got a bit out of hand due to unforeseen obstacles.

That all makes sense. I will do it the proper way as I have no interest in starting a fire and then getting into litigation with a deep pocketed insurance company.
I was hoping to avoid surface mounted conduit, however I think I can find a route that will keep the aesthetics acceptable. I have a series of 200mm concrete walls and 150mm floor slabs to drill through, but it should be easier than when I did the hole cutting for installation of a heatpump which required a series of 70mm holes.
I've found a link to a DC rated twin insulated cable, it appears to have a full double insulation. I'll ask the sparky if I can run both strings (2x twin cables) in the same conduit to save some drilling.

P.S.
Just to reassure you I will be working with a registered electrician (illegal to do otherwise in this country) but just trying to get my head in the right space before selecting one so I understand what is possible.

[Siwastaja]

I'll ask the sparky if I can run both strings (2x twin cables) in the same conduit to save some drilling.

I don't see any reason why you couldn't.

[nctnico]

I'll ask the sparky if I can run both strings (2x twin cables) in the same conduit to save some drilling.

I don't see any reason why you couldn't.

It can be done but if you look at the larger scale solar installs, you'll notice the red and black wires are ran in groups while maintaining a bit of distance between red and black. Keep in mind rodents are prone to chewing on cables as just one example what could go wrong with the wires long term. So if possible, I would use seperate conduits for black and red. In the NL the recommendation is the keep black and red seperated but no more than 10cm (to avoid creating a large loop area for EMC emissions and susceptibility).

[fastbike]

Keep in mind rodents are prone to chewing on cables as just one example what could go wrong with the wires long term.

There is a small amount of cable from the panel to the lead-in on the house which will be covered in flexi conduit as a guard against UV degradation (severe here in southern hemisphere). Then there will be a heavy duty PVC conduit where the cabling runs down the internal wall of my office, then through a 150mm concrete floor and into a service space adjacent to the stairs before going through a 150mm concrete wall and more wall mounted conduit to the inverter.

No rodents inside the house - I think dealing with my wife would be a bigger problem than chewed cabling if they did get inside !

[fastbike]

I'll ask the sparky if I can run both strings (2x twin cables) in the same conduit to save some drilling.

I don't see any reason why you couldn't.

I'm getting a bit closer to actually installing stuff. I've found an installer who is happy for me to contribute labour as sweat equity. He is fine with me running the two twin cables and the earthing wire (equipotential bonding required) in side of one conduit. He recommends 32mm PVC (it has to be HD grade).

We will be installing a "rooftop" disconnection box as permitted by local standards. This is actually a wall mounted IP56 (min) rated box with a 32mm conduit sealed into the back as the entry point into the house. 2 pairs of MC4 connectors for the two strings are panel mounted on the bottom side, for the rooftop cables to connect into. The conduit run inside passes down to the utility room and is installed with clearances/routing/labelling to conform to applicable local standards. The installer will take over from there.
I managed to legally get a free copy of all the relevant standards a few weeks back. That is super handy as now I can see what is permitted and what is forbidden (and often why).
This all gets inspected so needs to be done according to the book.

[fastbike]

I'll ask the sparky if I can run both strings (2x twin cables) in the same conduit to save some drilling.

I don't see any reason why you couldn't.

I'm getting a bit closer to actually installing stuff. I've found an installer who is happy for me to contribute labour as sweat equity. He is fine with me running the two twin cables and the earthing wire (equipotential bonding required) in side of one conduit. He recommends 32mm PVC (it has to be HD grade).

We will be installing a "rooftop" disconnection box as permitted by local standards. This is actually a wall mounted IP56 (min) rated box with a 32mm conduit sealed into the back as the entry point into the house. 2 pairs of MC4 connectors for the two strings are panel mounted on the bottom side, for the rooftop cables to connect into. The conduit run inside passes down to the utility room and is installed with clearances/routing/labelling to conform to applicable local standards. The installer will take over from there.
I managed to legally get a free copy of all the relevant standards a few weeks back. That is super handy as now I can see what is permitted and what is forbidden (and often why).
This all gets inspected so needs to be done according to the book.

32mm HD conduit installed with the IP66 rated disconnect box on the back wall of the flat roof that is adjacent to the panels. My wife helped me pull through cables for 2 strings and the earthing wire tonight, so is ready for the installer to terminate.
The next job is mounting the rails on the roof and earthing them. Unfortunately due to the nature of the roof (curved colorsteel) this requires two short rails for each of the 26 panels, so lots of earthing wires !. I've set aside two weekends for this part.

[nctnico]

Please make sure to use a safety harness + lines with hooks so you are strapped to a secure point on the roof. Falling down from the roof and hurting yourself is worse than spending a bit of money on safety. When I did my solar install, I used two lines with hooks so I always had at least one hook secured. I bought these from a reputable store, not Amazon / Aliexpress.

[fastbike]

Please make sure to use a safety harness + lines with hooks so you are strapped to a secure point on the roof. Falling down from the roof and hurting yourself is worse than spending a bit of money on safety. When I did my solar install, I used two lines with hooks so I always had at least one hook secured. I bought these from a reputable store, not Amazon / Aliexpress.

Yes, that is the first thing I bought. A decent harness with a fall arrester lanyard (I've also thought of what happens if the worst case happens and I'm left dangling 2m above the ground !).
I'm lucky that the house has a flat roof just behind and about 1.5m below the ridge of the monoslope where the panels will be installed. There are large 75x50 steel RHS brackets cantilevered off that will be perfect to secure the rope.
As I said to my wife, spending the rest of my life in a wheel chair is not something I'd like to do.
I'm also collecting some scaffold H frames tomorrow so I have a working platform at the lower edge of the roof (which is still 5m above ground)
Here's an elevation drawing of what the situation looks like.
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Edit: attachment not showing for some reason

[fastbike]

Elevation of roof