Solar Panel Wiring.

Any recommendations for cable rating from solar panel to controller and on to battery and where I can buy it?

Strictly, it's going to depend on a number of factors - the two most important being the size (i.e. wattage) of panel and the distance from panel to controller (and from controller to battery if you aren't able to get the two as close as possible together).

Other factors are location (probably partly external, so it will need to be UV-resistant) and also the nature of the route. In some cases (e.g. the install on our Trooper) the route from panel to controller can be very convoluted. That constrained us in terms of the largest size cable that we could use - bigger cable was not bendy enough for our installation.

You might also find that the controller itself makes things difficult for you, in that some have terminations that will only accept a maximum size cable (often, if the manufacturer is outside Europe, expressed in AWG rather than mm2). This isn't insurmountable, but it can be a bit of a pain when you're doing the wiring.

You may also want to consider dual-core cable, but it depends how you're going to install. If you have to go to a connector block on the panel itself it makes more sense to go with single-core cable, because you can take each of the two cables into the connector block, without any breaks in the 2-layer outer sheath/insulation. If you use 2-core you have to break into the outer sheath outside the connection block, which may compromise it. But... if you are simply splicing onto the existing leads of a panel after it has entered the van, dual core may be fine - in fact in that situation you really don't need a "solar" spec cable at all.

In our case we had a single 150W panel and almost 2m of wiring to get to the controller, and IIRC we used 4mm2 cable - we could not use anything thicker, and fortunately at that distance we didn't really need to (in reality, 2.5mm2 would probably have been perfectly adequate). The controller was mounted less than a foot away from the leisure battery, so cable sizing was not such an issue there.

Having said that, the best way to choose the right cable size for your specific install is to look in the documentation for the solar controller. Votronic, for example, has a table in the operation manual for their MPP range, and that gives recommended cable sizes for each of the different models in the range - which makes it pretty easy to choose a starting point.

Once you've decided on cable type and size, pretty much any reputable UK-based supplier will do. I would strongly recommend that you avoid Chinese sellers advertising (on Ebay, for example) UK stock. My experience of buying cable that way has not been good (in my case the markings on the cable were faked, and it was actually a much lower spec cable than advertised!).

I would use 4mm2 as a minimum from the panels to the regulator and the regulator needs to be as close to the batteries as possible to keep the cable from the regulator to batteries as short as possible, again 4mm2 is ok 

A good supplier of cables and accessories  is https://www.sunshinesolar.co.uk

As per Chris above, plus...

Photonic Universe, even if only for cables. They do extension cables with the correct connectors on one end to extend from the ones already on the panel to the solar controller. Generally 6mm2 x section but I've used these with no probs on their controllers

12v Planet.....for virtually everything electrical for caravan/motorhomes etc
You'll also get excellent inline fuses from them to connect the cable from the controller to the +ve terminal of each battery, AT the terminal itself so the unfused bit is as short as it can be

I used 21A twin core from them, each core is separately marked so as to avoid cross connecting.

Whatever you use, there is no disadvantage in going big, too big a cable is infinitely safer and better from the point of view of line losses than too small.

Another little tip ,if your cable run is say up to 5 meter long just buy a single 10 meter cable with the mc4 connection on each end and cut it in half to give 2 x 5 meter cables , it sometime saves a few £’s

I'll chip in and recommend Vehicle Wiring Products, they sell cables and a range of other items like fuse boxes that will be needed for a safe solar install.
https://www.vehiclewiringproducts.co.uk/

Since starting to watch bigclivedotcom on YouTube I'm becoming more cautious about buying electrical stuff on eBay and Amazon, although things manufactured in China can be safe many cheaper products can be death traps.
https://www.youtube.com/watch?v=sx60OYLt7EE

Roopert wrote:Strictly, it's going to depend on a number of factors - the two most important being the size (i.e. wattage) of panel and the distance from panel to controller (and from controller to battery if you aren't able to get the two as close as possible together).

Other factors are location (probably partly external, so it will need to be UV-resistant) and also the nature of the route. In some cases (e.g. the install on our Trooper) the route from panel to controller can be very convoluted. That constrained us in terms of the largest size cable that we could use - bigger cable was not bendy enough for our installation.

You might also find that the controller itself makes things difficult for you, in that some have terminations that will only accept a maximum size cable (often, if the manufacturer is outside Europe, expressed in AWG rather than mm2). This isn't insurmountable, but it can be a bit of a pain when you're doing the wiring.

You may also want to consider dual-core cable, but it depends how you're going to install. If you have to go to a connector block on the panel itself it makes more sense to go with single-core cable, because you can take each of the two cables into the connector block, without any breaks in the 2-layer outer sheath/insulation. If you use 2-core you have to break into the outer sheath outside the connection block, which may compromise it. But... if you are simply splicing onto the existing leads of a panel after it has entered the van, dual core may be fine - in fact in that situation you really don't need a "solar" spec cable at all.

In our case we had a single 150W panel and almost 2m of wiring to get to the controller, and IIRC we used 4mm2 cable - we could not use anything thicker, and fortunately at that distance we didn't really need to (in reality, 2.5mm2 would probably have been perfectly adequate). The controller was mounted less than a foot away from the leisure battery, so cable sizing was not such an issue there.

Having said that, the best way to choose the right cable size for your specific install is to look in the documentation for the solar controller. Votronic, for example, has a table in the operation manual for their MPP range, and that gives recommended cable sizes for each of the different models in the range - which makes it pretty easy to choose a starting point.

Once you've decided on cable type and size, pretty much any reputable UK-based supplier will do. I would strongly recommend that you avoid Chinese sellers advertising (on Ebay, for example) UK stock. My experience of buying cable that way has not been good (in my case the markings on the cable were faked, and it was actually a much lower spec cable than advertised!).

Thank you so much Roopert, a masterclass in solar wiring and it has given me all the information I need to complete my wiring with confidence.
I love this community and the shared knowledge so freely given.