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You can get near to 12mm² when the cable is made to comply with SWG I seem to remember it is still used for welding and automotive even in this country. Around 6 SWG.
The problem with the cable is finding lugs to fit, that's why I know it is around as I had to bring my hand crimper to my son as the hydraulic type would not crimp well enough, but the old manual type with a screw in the top could be adjusted to get a good crimp.
As to wiring a shed to my mind there is a massive jump in what is required when we exceed 13A. With a 13A FCU for the supply and a switched FCU with 3A fuse for the light switch it is a simple job. Once you exceed 13A then looking at a consumer unit in the shed etc. My shed just has a simple light and a socket for lawn mower.
Not sure about gland costs, but I think likely if I had 16mm² cable I would use it. The problem is 25 or 32 mm holes for glands but still likely cheaper than buying new cable.
We are told volt drop for lights no more than 3% but today LED lights can often work with as low as 85 volt with full output the problem is to convince some one testing and inspecting that it is OK. At 13A 2.5mm² is good for 32 meters with a volt drop of 6.9 required for lights. At 16A you drop to 25 meters. Next is 20A and one is clearly going to have to move to 4mm² and looking at 34 meters. As you move to 32A then again move up now to 6mm² limit is 32 meters. This is keeping within the 6.9 volt limit. So next is 40A and it drops to 24 meters with 6mm² but for sockets you could still run up to 41 meters staying within the 11.5 volt drop (5%) for non lighting supply. In real terms even with a 40A MCB or RCBO supplying the shed it would rarely hit the limit so to my mind after doing the calculations 6mm² is ample.
What you need to consider at 13A you may for an extended time run close to max, but as you go up in size then your less likely to be running at max.
The problem with the cable is finding lugs to fit, that's why I know it is around as I had to bring my hand crimper to my son as the hydraulic type would not crimp well enough, but the old manual type with a screw in the top could be adjusted to get a good crimp.
As to wiring a shed to my mind there is a massive jump in what is required when we exceed 13A. With a 13A FCU for the supply and a switched FCU with 3A fuse for the light switch it is a simple job. Once you exceed 13A then looking at a consumer unit in the shed etc. My shed just has a simple light and a socket for lawn mower.
Not sure about gland costs, but I think likely if I had 16mm² cable I would use it. The problem is 25 or 32 mm holes for glands but still likely cheaper than buying new cable.
We are told volt drop for lights no more than 3% but today LED lights can often work with as low as 85 volt with full output the problem is to convince some one testing and inspecting that it is OK. At 13A 2.5mm² is good for 32 meters with a volt drop of 6.9 required for lights. At 16A you drop to 25 meters. Next is 20A and one is clearly going to have to move to 4mm² and looking at 34 meters. As you move to 32A then again move up now to 6mm² limit is 32 meters. This is keeping within the 6.9 volt limit. So next is 40A and it drops to 24 meters with 6mm² but for sockets you could still run up to 41 meters staying within the 11.5 volt drop (5%) for non lighting supply. In real terms even with a 40A MCB or RCBO supplying the shed it would rarely hit the limit so to my mind after doing the calculations 6mm² is ample.
What you need to consider at 13A you may for an extended time run close to max, but as you go up in size then your less likely to be running at max.
