Wire gauge from battery bank to 12v panel?

[SKMT]

The positive and negative cables from my battery bank to 12v panel have insulation decaying off in a couple spots. It's welding cable about 1/0, I'm guessing it might be original to the 30 year old boat.

I'm just trying to figure out why I would need to replace it with the same 1/0 gauge wire? My windlass is direct wired (with it's own breaker). I just got a 2000lb davit, but the motor is AC.

So the biggest loads flowing through the 12v panel are FW pump, SW pump, macerator, 12v fridge. Then smaller stuff like fans, lights, etc. Even in a max burst situation, I don't see how I could surpass 30amps.

For 30 amps, at a 25ft round trip, Blue Seas wire gauge calculator recommends 6awg. Is anybody else running a similar gauge? Or does everybody just go way oversized?

[Shrew]

Are the batteries or cables running through engine spaces?

-> It's m understanding that you need to factor in 15% reduction in max current in engine spaces.

Is the welding cable AWG or SAE?

-> SAE wire is 6 ~ 12% smaller than AWG

While 6AWG is recommended for 30A @ 25' (@3% voltage drop), notice that you at the end of that range and going to either 30' or 40a moves you to 4AWG.

1/0awg is probably not necessary, but I would go a bit bigger than 6awg.

[Tomodore]

Size matters but also quality crimping and terminals and glue lined shrink wrap and marine grade wire.

[JimsCAL]

What about engine starting?

[Stu Jackson]

if you have a separate engine start bank and the wires from the house bank to the distribution panel don't ever feed the start, you are right, 30A would be all you'd ever see if you turned everything on all at once, not that that would ever happen.


#6 would work, many of our boats came with #4, still works on my boat.

[jamhass]

Capacity for future additions to the boat?

[SKMT]

Originally Posted by JimsCAL

What about engine starting?

There are separate wires for the engines, generator, inverter. This is strictly for the 12v panel.

[SKMT]

Originally Posted by jamhass

Capacity for future additions to the boat?

I'll probably add a 120v chest freezer, but that obviously is irrelevant. My electroscan is high amperage, but that's also direct wired with it's own breaker. I can't possibly think of any large amperage 12v additions... Maybe an oil change pump...not sure what they draw? But even in that case, I won't be taking a shower (running water pump) while i'm changing oil.

You tell me...besides windlass, what high amperage 12v toys do you have? (I'm guessing the windlass was originally wired thru the 12v panel, and that's why the original cable is so large.)

[Frankly]

My IP came from factory #4 with 60 A breaker. Doubt if the load has ever reached 30 amps and that probably for 20 seconds. All the other significant loads/ sources independent feed (SSB, Solar, alternator, inverter/ charger, starter, windlass).


Frankly

[sailorboy1]

My 50amp main DC panel is supplied through a #6awg cable. It is original and to tell the truth if I were to replace it I would use a larger cable. I never have been disappointed by having a larger wire size and the cost to step up is low.

[PerfectPirate]

Wire should be sized appropriate to the master breaker which controls the feed to the rest of the panel, or the breaker should be sized to the wire. So, are you feeding a 30 amp master breaker? If so, then, yes a #6 AWG cable will do the job. Heck if the run is short and direct, and not in an engine space, you could get away with a #8 AWG cable. If you are not feeding into a master breaker, then why not? Set up one of the breakers on your panel to be the master breaker controlling the power feed to all the rest of the breakers. This is an essential safety measure and part of the ABYC standards.


On my Blue Seas 8084 panel, the master breaker is 100 amps. So I need at least a #4 AWG cable running from the battery switch to the panel.

[kmacdonald]

Fuse it near the battery for whatever size wire you select. #6 AWG would be fine IMHO.