3 strands of 12 gauge VS 1 of 4

[Bycrick]

Despite all the doom-saying, hooking wires in parallel to carry more current is perfectly fine IF YOU DO IT PROPERLY. Simply fuse EACH wire at its proper size BEFORE you connect them in parallel.

What you CAN’T DO, is twist the wires together and then fuse the combination at the higher value appropriate for the two wires.

I saw one system with a very large alternator connected to a very large battery bank about 15’ away with 2/0 wire, which was too small. Given the local supply problems with bigger wire, he chose to run a second 2/0 wire of equal length in parallel. Each wire was separately fused with the appropriate fuse for 2/0 wire. Much cheaper and easier than pulling out the 2/0 and air-shipping in bigger wire.

So it can be done properly, but for small wires like #12, it’s probably way more work and expense than just buying the right-sized wire and fuse.

[W5PAD]

Originally Posted by BugzyCan

Is 3 strands of 12 functionally the same as one strand of 4? more or less? Will that extra insulation between the wires cause a problem somehow?
I was thinking even a single strand of 12 would be enough, since it is a 12v system, but I may as well use all three.
Thoughts? crazy?

Rule of thump: two wires in parallel will be equivalent to 2 AWG's less. For example - Two 12 AWG is the same as one 10 AWG. Two 10 AWG is the same as one 8 AWG. You'll need 16 x 12 AWG wires to have the same capacity as one 4 AWG wire. You don't need to strip the insulation.

[RJ 1946]

mcon12000; Good advice

[masteriti]

Originally Posted by BugzyCan

...I was thinking even a single strand of 12 would be enough, since it is a 12v system, but I may as well use all three.
Thoughts? crazy?

I noticed this a bit late...hope you are safe. Please fix your jerry rigged wiring asap!

(someone mentioned this already but it's worth emphesizing) For sizing wires, its the current (Amps) that matters. The current is determined by your load (i.e. the resistance of lights, autopilot, etc) on the circuit as well as the voltage of your battery.

Get a fuse at the positive terminal! This one don't want to ignore! Consider this: What if you don't have any load in your circuit (i.e. a short)? The resistance is eliminated (the wire resistance is negligeable) and you get a surge in current (like opening up the flood gates)...your Amps go through the roof and it will fry a 2/0 AWG wire just as easily. Here's a demo video:

https://www.youtube.com/watch?v=VwK6rCaEVL8

Don't trust the previous owner to have done the electrical work on your boat properly. Just because there's a 4awg wire there now, doesn't mean that's really what it needs.

Any change you make to your electrical affects may affect the whole system (i.e. what was in place and working before your 'additions' may not be able to work after your changes). Say you added a new light on a circuit...effectively increasing the length of your circuit with add'l wire. That will increase your Voltage drop on that circuit. lower voltage results in higher current (Amps). The old wire that's part of your new extended circuit may have been able to handle the previous current could now be overheating just due to voltage drop.