Cable from loft to CU

[Octopus]

OK. I'm a sparky but never dabble in PV.

Looking at a project for myself which will include a full refurb. Our budget does not stretch to installing PV but I plan to install a hi integrity board so the PV can be on a MCB or RCBO in the future. Cable run would be 10 m max

What I'd like to know is what size cable would you guys recommend I put in during the refurb so it can be concealed from day one.

Thanks

PS: If I've not included anything please point it out and ask!

 

[keniff]

I've only seen 2.5mm run on solar but might be bigger on bigger installs? I don't do it either lol

 

[matt.smallbone]

The solar systems I have come across have always had a switched fused spur as a local means of isolation with a 13 amp fuse in so I would run a 2.5.

 

[HandySparks]

I've never installed solar, but from what I've picked up, you need to decide first where the inverter's going, ie in the loft or somewhere downstairs near the CU. I also understand that the voltage drop limit for solar output circuits is 1%, in order to keep the inverter from shutting down on overvoltage. So, for example, with a 10m run on a 4kW installation, you'd have to go up to 4mm².

I'm sure someone 'in the business' will provide the definitive answer soon.

 

[SolarCity]

Go for 4mm² at least.

Inverters in lofts aren't a good idea in my opinion - a garage is a much better location.

 

[SPARTYKUS]

Over efficiency-tize it and use 16mm singles

 

[Octopus]

Go for 4mm² at least.

Inverters in lofts aren't a good idea in my opinion - a garage is a much better location.

Hum, taking the cable via the garage would add about 7/9 meters.

 

[SolarCity]

Hum, taking the cable via the garage would add about 7/9 meters.

It's a judgment call.

Inverters hate heat and dust. It affects their efficiency and their lifespan.

Europeans don't install in lofts - it's a British thing. 7/9 meters of extra cable will have very little affect on output as long as they're sized sufficiently.

 

[Octopus]

It's a judgment call.

Inverters hate heat and dust. It affects their efficiency and their lifespan.

Europeans don't install in lofts - it's a British thing. 7/9 meters of extra cable will have very little affect on output as long as they're sized sufficiently.

Thanks for the heads up - the PV is a distant requirement but putting in the cable is short term.

Thanks for the help.

 

[SPARTYKUS]

Thanks for the heads up - the PV is a distant requirement but putting in the cable is short term.

Thanks for the help.

Never thought of that before, its a great idea thank M.

 

[mydigitalhome]

I have used 4mm In the past and connected it into a wp wika box in the past for that purpose. As far as cable size is concerned its just a educated guess for a domestic install unless the house is incredibly large. However none of us are mind readers for the future as to what will be required. At least it's a start.

 

[Gavin A]

6mm2 cable is manufacturers recommendations for most high efficiency 16 amp / 4kWp inverters in order to limit the impedance between the inverter and the grid connection, though you will get away with 4mm2 and to an extent 2.5mm2 cable, you're storing up issues for further down the line when a few of your neighbours also have solar, and your inverter is the first to trip out on sunny days as the local grid voltage rises.

 

[Earthstore]

Strange, all you sparkies have only ever seen 2.5, if Inverter is going in the loft and your system will be up to 4KWP, without knowing the distance I would suggest 4mm minimum, but would recommend 6mm.

Just do the calculation for the length of cable run, 16A it needs to be below 1% loss as stated before, also try it at min and max AC voltage too, I think you will find that 6mm will be fine.

Also, a long, long story, but if you bury the cable it will need to go on it's own dedicated RCD, not a shared one.

I hope this helps.

 

[SPARTYKUS]

10mm. Over 10 years that extra 0.2% will pay back

 

[Megavolt]

6mm defo. Can't see how there getting away with 2.5 bet calcs don't add up