Hi all, I have the following cable for my 220v section of my off grid electrical install. I am going to have surplus. I'm no electrician by any means. Would I be able to use this cable for the 12v runs too?
https://www.electriccable.co.uk/RWD...1DGCBg7mAOj4pjPSzv27ulbdeOybVHh-XcNiiST0npe54
It really isn't that straightforward to answer, especially as the link you have points to many different cable sizes... 1.5mm, 2.5mm, 4mm, etc.
The determinants of suitable cable selection are current draw and cable length - particularly for very low voltage (e.g. 12v) systems. In general, the greater the current being drawn, and the longer the run of cable, the greater the cable's cross-sectional area must be.
If you're going to be running a couple of led lamps of (say) total power of 5W, then the current draw will be 5W/12V = slightly less than 0.5Amps. According to regs, a 1.5mm cable would be more than adequate for this.
However, if you're looking to power (say) a Truma boiler, the current required for that could be10-15 Amps, according to the type of boiler. At that sort of current, you're going to need at least 2.5mm cable, in theory. BUT... the length of the cable now becomes very important at these higher currents. The longer the cable, the greater it's resistance, the greater the heating effect on the cable, and the greater the voltage drop.
For example, because of problems I'm having, I checked the voltage drop across the cable supplying power to my Truma boiler: at the supply (
battery) end, there was 13.3V, but at the boiler end of the same length of cable, when the boiler was running at max blower speed, I was only seeing 10.2V... low enough for the boiler to cut out. This is without being on EHU (though, in theory, that wouldn't affect the voltage drop on the cable; it would only ensure the
battery voltage remains high enough to overcome the voltage drop). In my van, the boiler has been connected using 2.5mm cable. I've had to rewire it with 6mm cable to keep it running more reliably.
Finally, circuit fuses at the power supply (
battery/power controller) end are solely for the protection of the cable; NOT for the protection of any devices connected to the cable. So don't think that you can use a 20A
fuse on a 1.5 mm cable supplying a high power appliance. The cable would likely burn out before the
fuse!
A long post, for which I apologise, and congratulations if you made it this far! Tell us what you're planning to run, and you'll get more reliable advice.
