# Comments and wire sizes



## Garystan (Nov 17, 2014)

What I have now is a 16’ Polar Kraft. One battery in the rear with main wires that go to a switch panel that is 1/3 of the way up front. From there I have wires that go to the front bow and rear stern lights, wires that go to my bilge pump, and wires that go to my depth finder. My trolling motor wires go directly from the battery to the trolling motor, up front. If I need to hook up my electric start motor I do so directly to the battery. 
I would like to add a battery and move both up front for weight reasons. One for the trolling motor and the other to run everything else, starting battery. The deep cycle for the trolling motor would only be about 6’ away from my trolling motor outlet. What size wires would I need (70 thrust 12 volt)? The starting battery would have main wires going back 2/3 to the switch panel and from there to the bilge, fish finder and lights. So what type of wire would I run to the switch panel and what size wires to the other items? Also, I would run wires direct from the starting battery to some sort of terminals in the rear so I could hook up my 25 HP electric start to that. What size wires would I nee for that? I will also add a battery shut of switch so I can turn both batteries off when not in use.
So I need sizes and comments on the wiring itself. Thanks in advance.


----------



## BigTerp (Nov 18, 2014)

You will need to know the amp draw for each item you are wiring. Once you know that you can use the chart below to find out what size wire you will need. For your trolling motor and big motor your manual should tell you what size wire and fuse/breaker to use for each. I recommend high quality tinned marine wire and heat shrink connectors for everything on your boat. The only place I didn't use the above was for my speakers. Those wires/connections have corroded and given me problems ever since. I finally redid my speaker wiring with tinned marine wire and haven't had any problems since.

https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity

You will also need to take into consideration fuses for each wire or a fuse/circuit box to protect your wires. The size of your fuses will, again, be based on your amp draw. 

There are a bunch of good threads on boat wiring within this forum. Try the search function and you should have enough reading for the rest of the day.

Here is one when I started my wiring project. I had zero clues on what I was doing. Now I consider myself somewhat proficient with boat wiring. I still hate electricity though!!

https://forum.tinboats.net/viewtopic.php?f=5&t=31069&hilit=wiring


----------



## Garystan (Nov 18, 2014)

BigTerp said:


> You will need to know the amp draw for each item you are wiring. Once you know that you can use the chart below to find out what size wire you will need. For your trolling motor and big motor your manual should tell you what size wire and fuse/breaker to use for each. I recommend high quality tinned marine wire and heat shrink connectors for everything on your boat. The only place I didn't use the above was for my speakers. Those wires/connections have corroded and given me problems ever since. I finally redid my speaker wiring with tinned marine wire and haven't had any problems since.
> 
> https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity
> 
> ...


----------



## BigTerp (Nov 19, 2014)

If the manual for your trolling motor calls for 6 gauge go with that. it should also tell you what size fuse or breaker you need. Yes, you have to figure round trip for wire size. If your trolling motor is 6' away from your battery, you have to call it 12' to reference the chart I linked. Same thing with all of your accessories. Also, if you're close to the next highest AWG wire size, go with it. Bigger is better than too small. Most of my accessories called for 16 gauge wire, but a few like my stereo and bilge pump, called for 14 gauge wire so I used 14 gauge for all of my accessories. Just made things easier.

Not sure what motor you have, but 12 gauge wire would be way to small for an outboard electric starter. That 20 amp fuse is not for your starter. It is most likely for part of the electrical system on your outboard. The starter should run directly off your battery. A 2-stroke outboard can draw 100+ amps while cranking. If you were having fuel issues or something and cranking for an extended period of time you could easily fry that 12 gauge wire and start a fire. Do you have a manual for your motor? It should tell you exactly what size battery and wire you need. I have a 1994 50/35 Johnson. It calls for a battery with at least 360 CCA (465 MCA) and 4 gauge wire. I have a group 27 battery rated at 750 MCA and used 4 gauge wire for about a 10' run.


----------



## Moedaddy (Nov 24, 2014)

4 ga. Or bigger will work on the t-motor and for cranking the outboard


----------

