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Old 12-05-2015, 08:18   #1
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Wire size from Battery to panel, 26' sailboat

I have a 1970 Columbia 26 that I am re-wiring as the original panel is shot. In the existing configuration, there is a # 12 awg wire connecting the battery to the panel.

Loads are as follows:

Convenience outlet and existing fuse sizes per circuit:
searchlight 10 amps
stereo: 6 amps
auto pilot : 5 amps
depth finder 3 amps
inverter 300 watts 12 amps?? never really use it.
lights: cabin 3 amps
running lts 3 amps
mast light 3 amps
instruments 3 amps

Each of these will be placed on a new 15 amp circuit. It seems like the wire from the battery to the main on off switch, and from there to the panel should be larger than 12 awg, although the loads are low. any advice? Distance from battery to switch is under 48".


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Old 12-05-2015, 19:38   #2
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Re: Wire size from Battery to panel, 26' sailboat

In short, you are probably good with 4awg.

In long:
300w inverter should be fused for 30amps. I also wouldn't normally fuse an inverter through your main panel. You may want to consider fusing it locally and controlling the on/off with the battery switch.
assuming your panel is within 12 feet of wiring to the batteries, 4awg wire will give you a 3% volt drop at 12 volts with a total circuit length of 25 ft. For about a 60 amp rating.
Just for reference. You also want to take future expansion into consideration.
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Old 12-05-2015, 20:08   #3
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Re: Wire size from Battery to panel, 26' sailboat

Quote:
Originally Posted by bellrock View Post
I have a 1970 Columbia 26 that I am re-wiring as the original panel is shot. In the existing configuration, there is a # 12 awg wire connecting the battery to the panel.

Loads are as follows:

Convenience outlet and existing fuse sizes per circuit:
searchlight 10 amps
stereo: 6 amps
auto pilot : 5 amps
depth finder 3 amps
inverter 300 watts 12 amps?? never really use it.
lights: cabin 3 amps
running lts 3 amps
mast light 3 amps
instruments 3 amps

Each of these will be placed on a new 15 amp circuit. It seems like the wire from the battery to the main on off switch, and from there to the panel should be larger than 12 awg, although the loads are low. any advice? Distance from battery to switch is under 48".


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Be good to install an ANL fuse, within 12" of the battery + post, so a 70 amps fuse would be good.


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Old 12-05-2015, 20:48   #4
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Re: Wire size from Battery to panel, 26' sailboat

We have 2 banks of 24 VDC & 360 AH each. Each main leg is fused 300 amps on 2-0 wire about 4 feet long. You can't error by using larger wire. Good advice above I think on the #4 if you keep it short. Use the marine rated pre-tinned wire. If you care to deal on line or by phone, look up Wolf's Marine in Benton Harbor, Michigan. Many panels, breakers, wire by the foot.
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Old 13-05-2015, 09:50   #5
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Re: Wire size from Battery to panel, 26' sailboat

A few good suggestions have been made. I agree that a #4 or 6 AWG lead from the battery is about right. I would go with the #4. I would also install an inline 30 amp fuse upstream of the distribution panel or positive buss. A separate fuse for the inverter is not a bad idea, either.

Some of your loads seem a bit high. I'm guessing much of the hardware is a little older (incandescent lights, older auto pilot, that sort of thing). I would look at upgrading to LED cabin lights and maybe a newer auto pilot. My Ray Marine ST1000+ only draws 185 mA and it took us to Hawaii on a Moore 24 last summer.

So, bottom line: #4 AWG from the battery to the panel with an inline 30 amp fuse ahead of the panel. If you use the inverter, then an line fuse for it, too. Otherwise, why not take it out? Oh, yeah...a good non-conductive dialectric grease on all connectors on the back of the panel. It will prevent corrosion and keep connectors clean (thus reducing the resistance and load on each circuit).

Enjoy sailing your boat.
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