A matching size ground cable needs to be connected between the engine trans combination and the frame for vehicles with short ground cables from the battery to the frame and those with a ground cable running all the way to the starter.
Car battery ground cable size.
A braided copper ground strap is best attaching the engine to the frame.
Wiring sizes measure from smallest to largest on a numerical scale with zero for the largest size of wire and larger numbers as the wire size decreases.
Copper conductor ampacity based on 75 c 167 f reference.
Choosing the correct gauge automotive wire depends on the acceptable voltage drop length of the feeder branch circuit conductor load amperage and the ambient temperature of the compartment where the primary wire will pass through.
The fine stranded wire will pass more amperage than course stranded wire that has a lower strand count.
The following maximum amps versus cable size awg come from the nec version 2011.
Battery wire size per voltage amperage load and length chart below shows minimum cable size to use awg wire.
Cable size ampacity chart.
Fine stranded stereo wire makes great battery cable giving the best gage wire for proper battery charge.
Choose a higher ambient temperature when conductors are expected to pass through.
As far as i know these values are valid as of today.
Outside engine compartments the ambient temperature should generally be 20 c.
The manufacturers make stock battery cables as small as possible but still get the job done.
For more detail though check with the national electrical code as well as your own zoning laws.
This diagram illustrates proper vehicle grounding both to the engine block and also directly back to the battery as your vehicle s steel frame has only 20 of the conductivity as.
Going up a size or 2 is worth it in the long run.
For very long cables for example 15 foot long battery cables to relocate your battery go one size larger.
In summary when selecting the correct size of battery cable you need to take into account the total maximum amperage your electrical system requires the voltage of your system usually 12 volts the total length that your cables need to be and the amount of voltage drop you are willing to accept versus the amount you want to spend.
Most of the cost is the ends and labor.
I recommend building cables larger than stock.
The photos and captions chronicle the installation of an optima battery in a bitchin finned aluminum battery box within the trunk of my deuce hi boy roadster.
