4 Gauge 4 AWG 25 Feet Red + 25 Feet Black ( 50 Feet Total ) Welding Battery Pure Copper Flexible Cable Wire -- Car, Inverter, RV, Solar by WindyNation

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The point is, the only information that’s useful is the cross-sectional area of the cable. Everything else is misleading rubbish. You might think I’m being unfair. Okay, let’s increase our cable run by just one metre, to 3 metres. What happens? The required cross-sectional area jumps to 2.30 sq. mm, which means you have to use the next size up… 12 AWG. Obviously the cable carries the current, so the cross-sectional area of the copper wire is super-important when you’re trying to size a cable. This allows for a 3% voltage drop through the cable, which is acceptable for most automotive wiring jobs (3% of 12 volts = 0.36 volts). It’s a good guide. If nothing else, this value gives you an idea of how much power you’re losing in your cables. Say you’re losing 5 Watts through your fridge cable, and say your solar panel is producing 100 Watts and powering your system.

Ampacity Calculator - Wire Size Calculator Wire Ampacity Calculator - Wire Size Calculator

Use the calculator below to figure out the cross-sectional area of the cable, then use the Cable Size Chart to match it to the nearest size. Auto cable like the SCA example above also uses the 5mm cable terminology. But auto cable is referring to the overall diameter, insulation included , not the cross-sectional area. Buy cable with an AWG size. This is an American Standard for cable sizes and you’ll likely get the correct cabling for the job. The AWG tables are for a single, solid and round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.

Say you run a positive cable from the battery to a compressor. Distance is 2 metres. If you run the negative to ground from the compressor at the compressor, then total cable length is 2 metres (plus a bit for the negative cable). Most suppliers of auto cable don’t though. So you have no idea of what the cross-sectional area is. You’ll notice under the Voltage Drop box it says, “Max. 0.36V for 6 AWG & 16 ISO cables and smaller. Max. 0.24V for 4 AWG & 25 ISO cables and larger.”. Now, if we change the cable run to 20 metres, then the cable cross-sectional area needed is 15.3 sq. mm. This corresponds to 16 ISO or 4 AWG cable.

Cross Reference AWG to MM2 | Multi/Cable Corporation Cross Reference AWG to MM2 | Multi/Cable Corporation

So use 0.36 volts for smaller cables (6 AWG/16 ISO and smaller) and 0.24 volts for large cables (4 AWG/25 ISO and larger).If measuring a single strand is too difficult, measure the diameter of the whole bundle. It’s not as accurate but will give you an indication at least. Just make sure you go down a cable size if you do this. Then 5% of the power produced by the solar panel is simply generating heat in the cable. You might decide this is acceptable or you might decide to increase the cable size for your fridge supply. The hotter the cable, the more voltage drop through the cable. If you’re running a cable from a battery under the engine bay, it can get pretty hot… like 70 deg C or more. The problem is, most of the AWG sizes they’ve listed don’t match the cross-sectional areas. At least they specify the cross-sectional area I suppose… This brand gives a lot more information, but it’s not too clear. “24 x 0.2mm” means 24 strands of 0.2mm diameter wire. Using the Cable Area Calculator above, this equates to 0.75 sq. mm cross-sectional area, which is actually just under 10% smaller than 18 AWG. So even this isn’t accurate.

Wire Size Chart and Maximum Amp Ratings - Wire Size Calculator

If you can’t measure an individual strand, then measure the diameter of the bundle. It’ll at least give you an indication of the cable’s size.So if your sparky mate says you need 5mm cable, he’s referring to ISO cable. If you buy auto cable instead, then you’ll most likely buy cable way undersized for the job… and wonder why your fridge keeps cutting out. Change the temperature, if necessary. The value should be the maximum operating temperature that is expected for the wire. Select the wire conductor material, either copper or aluminum. You can also use Advanced mode to set a custom material resistivity at a fixed temperature.