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Author Topic:   Wire Gauge
Loafer posted 06-12-2008 07:32 PM ET (US)   Profile for Loafer   Send Email to Loafer  
Jim, thanks for the timely article about starting circuits. Any suggestions on the high current wire gauge from the battery? I've got a Mercury 150 with about 12 feet of run from the battery switch to the starter solenoid and either three feet or eight feet from the two batteries to the switch. The negative cable will be at most about 16 feet long.

I'm thinking #2 gauge should do it. Confirmation or other suggestions would be appreciated.



jimh posted 06-12-2008 09:39 PM ET (US)     Profile for jimh  Send Email to jimh     
Selecting an appropriate wire gauge for the engine starter motor wiring depends on two factors:

--the current carrying capacity needed in the wire
--the maximum tolerable voltage drop in the circuit

When you lengthen the cable run beyond the usual three-foot length, the voltage drop become the dominant factor in cable selection. You will end up using much larger cable (with a much higher current capacity than actually needed) in order to prevent excessive voltage drop in the long cable.

Usually the outboard motor engine manufacturer will provide guidance on the wire gauge needed as a function of the wire length to provide proper starting current and voltage. Some marine electrical manufacturers have a web-based computer that can help calculate the correct size wire. This prior discussion on the topic gives some good links:

Loafer posted 06-13-2008 06:00 PM ET (US)     Profile for Loafer  Send Email to Loafer     
Thanks, Jim.

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