EVINRUDE 2010 RECOMMENDED BATTERY CABLE SIZE FOR E-TEC ENGINES
Distance CONDUCTOR SIZE by MODEL
in Feet 15 to 30 HP 40 to 300 HP
1 to 10 6-AWG 4-AWG
11 to 15 4-AWG 2-AWG
16 to 20 2-AWG 1-AWG
These recommendations are a good guideline to use if the cables between the engine and its cranking battery are to be lengthened, as often occurs when the engine cranking battery is relocated to the center console from the transom area. Note that the recommended cable size is for a cable made entirely from that wire gauge, not for cables that mix wire gauges. As a general rule, if you move the engine cranking battery to the console, you will have to abandon the original battery cables used for installations where the engine cranking battery was at the transom and a few feet away from the engine. You cannot splice on added conductors to the original engine cables and meet the recommended wire gauge.
For example, if the distance between the battery and the engine is 20-feet, the recommended wire gauge is 1-AWG. This does not mean that you can use original cables of 4-AWG for 6-feet of the run and splice them with 14-feet of 1-AWG. The whole run should be 1-AWG.
CALCULATING WIRE RESISTANCE IN RECOMMENDED CABLES
From this recommendation we can deduce the maximum allowed resistance in the cable. A wire of 1-AWG has a resistance-per-1000-feet of 0.1239-Ohm. The resistance of 20-feet of 1-AWG will then be:
0.1239-Ohm/1000-feet x 20-feet = 0.002478-Ohm
If part of a cable consists of 4-AWG wire, that segment will already have significant resistance. A wire of 4-AWG has a resistance-per-1000-feet of 0.2485-Ohm. The resistance of 6-feet of 4-AWG will then be:
0.2485-Ohm/1000-feet x 6-feet = 0.001491-Ohm
In the recommended cable size and length, the total resistance is limited to 0.002478-Ohm. If the 4-AWG wire already contributes 0.001491-Ohm, then the remaining cable must not have a resistance greater than
0.002478-Ohm - 0.001491 = 0.000987-Ohm in a 14-foot cable
Scaling this for Ohms/1000-feet we get
(0.000987-Ohm/14-feet) x (1000) = 0.0705-Ohm/1000-feet
Looking for a size size with a resistance of 0.0705-Ohm/1000-feet, we see that wire of 00-AWG has a resistance of
0.079-Ohm/1000-feet (00-AWG)
and this is greater than the necessary maximum resistance (0.0705-Ohm/1000-feet). The extension cables would need to be made from 000-AWG. 000-AWG has a resistance of 0.0618-Ohm/1000-feet, and a 14-foot length would then have a resistance of 0.0008652-Ohm. We see that the total cable resistance in a combination of 4-AWG and 000-AWG would be as follows:
4-AWG cable for 6-feet = 0.001491-Ohm
000-AWG cable for 14-feet = 0.000865-Ohm
TOTAL CABLE RESISTANCE = 0.002356-Ohm
We next compare the resistance of this combination-size cable with the recommended 1-AWG cable:
20-feet of 1-AWG = 0.002478-Ohm
20-feet combo-cable = 0.002356-Ohm
We see that our combination cable has a lower resistance than the recommended cable. That is good because there will be some added resistance in the connection between the two pieces of cable, such as a terminal post and connectors.