Battery cable gauge

skunkedskippy

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I’ve read that the cable gauge should be determined by the length. But if you have multiple runs of different lengths is ok to have different gauges?

For example, let’s say the run from my battery to the selector switch is 6 feet so I use 1 gauge. Then the run from the switch to starter is 3 feet. Do I use 1 gauge to match the longer run or can I use a smaller gauge?
 

alldodge

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The gauge is determined by the total length from the battery to the starter. Anything put in between those points just adds length. You should look it your case listed the gauge size for 9 feet
 

skunkedskippy

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Thanks guys that make perfect sense. But Scott how did you get 18 from 6 plus 3? Are you adding positive and negative together?
 

Scott Danforth

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6 + 3 + 3 + 6 = 18.... simple math.
 

skunkedskippy

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If I have dual batteries do I have to double the length on top of that?

Scott can you help me with the math?
 

Scott Danforth

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If I have dual batteries do I have to double the length on top of that?

Scott can you help me with the math?

still size it for 9' there and 9' back as your dual batteries join at the switch.

not sure which boat you have, however with an I/O your probably looking at 2 gauge at a minimum
 

skunkedskippy

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Mercruiser 5.7 with 2 ga from previous owner. Battery 1 has a total run of 11 feet and battery 2 has a total of 15.

My mercruiser manual specs specs the following:
up to 3.5’ = 4
3.5-6’ = 2
6-7.5’ = 1
7.5-9.5’ = 0
9.5-12’ = 00
12-15’ = 000
15-19’ = 0000

Is this the absolute rule to follow? Seems like going from 2 to 0000 is a bit excessive. What types of issues could you see with undersized cables?
 

Grub54891

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Undersized wiring will cause connections to get hot, and burn/melt. Even the wires themselves will get hot, good way to start a fire. Starters require all the amps they can get. Now if your ground goes on a short run to the block, you may not have to double the run length? Someone correct me if I'm wrong.
 

alldodge

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Mercruiser 5.7 with 2 ga from previous owner. Battery 1 has a total run of 11 feet and battery 2 has a total of 15.

My mercruiser manual specs specs the following:
up to 3.5’ = 4
3.5-6’ = 2
6-7.5’ = 1
7.5-9.5’ = 0
9.5-12’ = 00
12-15’ = 000
15-19’ = 0000

Is this the absolute rule to follow? Seems like going from 2 to 0000 is a bit excessive. What types of issues could you see with undersized cables?

I can agree, my Formula is using 000 an the run is probably 20 feet (bat, switch, starter) so a bit under but has no issues

000 = .409 diameter
0000 = .460
 

skunkedskippy

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Thank you all for your input. I ended up going with 00. West Marine has a 50% off sale on all Ancor wiring. Also used their price match to get 25 pack of lugs for $40.

One of the the employees had a crimp tool so I crimped all my lugs right there. I’ll probably coat the connections with liquid electrical tape then wrap with adhesive shrink wrap.
 

skunkedskippy

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Apr 30, 2017
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A couple pics. Because I’m bored. 😏
 

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