Alternator wire sizes

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NYSail

NYSail

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Jan 6, 2006
3,181
Beneteau 423 Mt. Sinai, NY
Hello all....
I added a starer solenoid over the weekend and ended with just looking at all my wiring and noticed the following and was hoping for input from the experts.

I have three battery banks; one in the front of the boat that powers bow-thruster (I know) and windlass (One group 31) and then two in the back; one house (2 group 31) and a reserve (1 group 31). I have an Balmar 70 amp alt with external regulator newly installed last year. Also, the front bank is tied together via an isolator (this is scheduled to be changed to a combiner).

The wires run as follows: from the alt to the isolator with a #6 gauge wire about a 3 foot run. from the isolator to the bow bank about a 12 foot run with a #6 gauge wire, then a #10 gauge wire back to the starter post about 3 feet that feeds the 2 rear banks with a #10 gauge wire. The last #10 gauge wire is my question.... seems very small to feet 3 group 31 batteries.

Thanks!
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
It is. Even if your 70A alternator doesn't reach 70 amps for your relatively small house bank. Since you seem so knowledgeable, have you not been able to find wire sizing tables? West Marine has one in their catalogs and publish online in their Advisors: http://www.westmarine.com/webapp/wc...catalogId=10001&page=Marine-Wire#.UdMD5pzfL_I

Maine Sail has posted a link to another one, but I don't have it handy, but Google wire sizing online and I'll bet you'll find one.

Is that what you're looking for or do you want us to size it for you? :)
 
NYSail

NYSail

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Jan 6, 2006
3,181
Beneteau 423 Mt. Sinai, NY
Well when it comes to electrical I am not that knowledgeable...... I know what I don't and hate to electrocute or burn down things due to ignorance. That's why I ask for advise.... no stupid questions.

I did see the table and felt that at least a #8 was needed and probably a #6. I was just a little perplexed that the electrician that installed the alt. did not change the wire..... Prior it was a 35 amp alt. so I guess it was fine then. And yes I always like to hear the opinions of people that know electrical like some on this site do.....

Thanks as always
Greg
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
Greg, that bit of "history" (someone changed your alternator in the past) is helpful.

For me personally, boat mechanic and boat electrician seem to be oxymoronic phrases, 'cuz except for Maine Sail and one other fellow here in the Bay Area, I haven't found any good boat electricians, so I read their stuff and learned how to DIY. Not so say there aren't any, just not too many Ive heard of or else we wouldn't read all these electrical posts, now would we??? :):):)

You're right about questioning your wire sizes and I hope I've given you enough information to check it out.
 
NYSail

NYSail

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Jan 6, 2006
3,181
Beneteau 423 Mt. Sinai, NY
Well you did Stu. And yes I fully agree about the mechanics, electricians etc...... I do as much as I can after reading as much as I can and after questioning as many people as I can. That's why I love this site....
I've basically taken my entire boat apart for an almost complete refit. I just added the solenoid for my starter after reading all the posts... yes I know simple stuff. I do most of my engine work myself as well....

Again thanks!!
Greg
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,760
Canadian Sailcraft 36T Casco Bay, ME
Greg,

Will give you my thoughts when I get home. Knee deep in 4/0 wire right now.....
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
So the difference between a rank amateur asking for advice and a professional (he gets paid for it) marine electrician is the amateur is not afraid to ask a question?
I'd say yes it is too small. And congrats to making it to the league of professional (the pay stinks on DIY don't it) marine electricians.
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
Actually, Bill, I think the pay for a DIYer is much better.

You don't have to pay twice to get it done right once. :)

We're glad Greg asked.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,760
Canadian Sailcraft 36T Casco Bay, ME
Greg,

Sorry scuh a short response but I have to run back out to finish a solar install to have the customer ready for the holiday.

1- Yes wires are much to small.

2- Lose the isolator as it is likely causing unwanted voltage drop. It is rare that folks wired them correctly.
 
NYSail

NYSail

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Jan 6, 2006
3,181
Beneteau 423 Mt. Sinai, NY
As always... Thanks for the help!!

And btw I love being a DIYer...... Pay is great!!
 
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