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Old 10-09-2008
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Alternator wire gauge

My alternator is currently set up to charge my starting battery through the starter on the engine. I'm going to hook up an Echo-Charger, so apparently I need to re-wire the output of the alternator to my house bank.

My question is what size wire do I need for this? The current wire making the short (< 1ft) run to the starter is quite small (12 gauge?). If I'm going to wire the output to the house batteries, do I need to buy a larger gauge wire to make the run ($$$)?

The total run will be around 8 ft (via a bus bar). I think the alternator is a 55 amp.

Also, do I need to include a fuse in the wire? (if so, what size?)


Last edited by myster; 10-09-2008 at 03:02 AM.
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Old 10-09-2008
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Balmar recommends you use at least AWG4 wire for up to a 15ft run. Note that this is the total run, i.e., from the alternator to the battery and back.

ABYC also says a fuse is a good idea. It should be located near the battery, not near the alternator. Size the fuse for at least 140% of the alternator capacity (or about 80A in the case of a 55A alternator).

Here's what Balmar says:

Note: Fusing is designed to protect the boat and its wiring from the constant potential energy stored in the battery, rather than output from the alternator. Fusing should always be installed at the end of a wire or cable run closest to the battery. DO NOT place fusing for the alternator’s output cable at the alternator end of the cable run!
We find that a circuit protection device sized at approximately 140% of your alternator’s rated amperage is typically suitable for the circuit being protected. For more info about circuit fusing, see


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Old 10-10-2008
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Thanks for the info. I'll have to fork out some $ for cables. Is there a DIY way to make battery cables without having to buy an expensive terminal crimper? I'd hate to purchase an expensive tool for something I'll only be doing once.
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Old 10-10-2008
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Blue Sea has a wire size calculator that might help. Google "Blue Sea wire calculator".

Our local chandlery makes up cables using the right tinned multistrand wire, properly crimped, heat shrink. Just need to get the length and lug sizes right for them.
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Old 10-10-2008
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I got all my stuff off ebay A guy sells fantastic wire with all the marine ratings and the best heavy duty cable lugs I have ever seen.
He has a hammer crimper that works well. I bought a multi crimper that you hit with a hammer with no brand name that was half the cost of west marine, when it came it was an ANCOR brand. Also buy the triple walled pre glued shrink tubing. Really finishes the job well. The heavy duty stuff did so much better than the thin tubing
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