What Gauge Wire from Battery to Starter?

When the connection between the vehicle’s battery and the starter is not strong enough, you might experience some starting issues. It is vital to connect the battery and starter with the right wire size. So, that is why today, I’m going to give you some tips on what gauge wire to use from your battery to your starter.

In general, for proper functionality, follow the below gauges for the right battery starter cable size.

  • Use a 4 gauge wire for the positive battery terminal.
  • Use a 2 gauge wire for the negative battery terminal.

That’s it. Now your vehicle will receive constant power.

Let’s go into more detail below:

Need to Know Factors About Battery Cable Size

chris fix showing the gauge wire that connects battery to starter
Video | ChrisFix

Before you jump to any conclusion, you need to realize a few things. Choosing the right wire gauge entirely depends on two factors.

  • Carrying load (current)
  • Length of the cable

Carrying Load

Usually, a starter motor is capable of producing 200-250 amps. Since the current is extensively large, you’ll need a large enough conductor. If the cable is too thick, it will produce more resistance and disturb the flow of the current.

Tip: The Resistance of the wire depends on the length and cross-sectional area of that particular wire. So, a thick wire has more resistance.

If the cable is too thin, it might lead to short circuits. So, choosing the right cable size is crucial.

Length of the Cable

Howcast diagnosing car battery and starter problems
Video | Howcast

When the wire length increases, the resistance increases automatically. According to Ohm’s law,

V = IR

Therefore, the voltage drop increases too.

Acceptable Voltage Drop for 12V Battery Wires

When using a 12V battery with AWG wires, the voltage drop should be below 3%. Therefore, the maximum voltage drop should be,

12V × 3% = 0.36V

Remember this result; you’ll need it when choosing battery cables.

Tip: AWG, aka American Wire Gauge, is the standard method to determine the wire sizes. When the number is high, the diameter and thickness get smaller. For instance, 6 AWG wire has a smaller diameter than the 4 AWG wire. So, the 6 AWG wire will produce less resistance than the 4 AWG wire. (1)

What is the Best Gauge Wire for Battery Starter Cables?

chrisfix showing a car starter
Video | ChrisFix

You know that the right cable size depends on the current and the distance. So, when these two factors change, the wire size might vary too. For instance, if a 6 AWG wire is enough for 100 amps and 5 feet, it won’t be good enough for 10 feet and 150 amps.

You can use a 4 AWG wire for the positive battery terminal and a 2 AWG wire for the negative battery terminal. But, accepting this result straight away might be a little confusing to you. So, here is a detailed explanation.

What We Learned So Far:

  • Starter Motor = 200-250 amps (assume it as 200 amps)
  • V= IR
  • Acceptable Voltage Drop for 12V Battery = 0.36V

Based on the above three base results, you can start checking the 4 AWG wire. Also, we’ll use the distance as 4 feet, 7 feet, 10 feet, 13 feet, etc.

The 4 AWG wire resistance per 1000 ft = 0.25Ω (approximately)

Therefore,

Resistance per 1 ft = 0.00025Ω

At 4 feet,

wire resistance calculator

Click Here for the Wire Resistance Calculator.

Resistance of the 4 AWG wire = 0.001Ω

Therefore,

V = 200 × 0.001 = 0.2V

At 7 feet,

Resistance of the 4 AWG wire = 0.00175Ω

Therefore,

V = 200 × 0.00175 = 0.35V

At 10 feet,

Resistance of the 4 AWG wire = 0.0025Ω

Therefore,

V = 200 × 0.0025 = 0.5V

As you can understand, at 10 feet, 4 AWG wire exceeds the acceptable voltage drop. So, you’ll need a thin wire at 10 feet.

Here is the complete chart for distance and current.

 Current (Amps)4ft7 ft10 ft13 ft16 ft19 ft22 ft
0-2012121212101010
20-35121010101088
35-501010108886 or 4
50-651010886 or 46 or 44
65-8510886 or 4444
85-105886 or 44444
105-125886 or 44442
125-15086 or 444222
150-2006 or 444221/01/0
200-25044221/01/01/0
250-3004221/01/01/02/0

If you follow the above chart, you can confirm our calculated results. Most of the time, the battery starter cable might have a distance of 13 feet. Sometimes, it can be more. However, 4 AWG for the positive terminal and 2 AWG for the negative terminal is more than enough.

Frequently Asked Questions

Is It Okay to Use Small Battery Cable Size?

Small AWG wires have higher resistance. So, the flow of current will be disturbed. 

Can I Use a Too Big Battery Cable?

When the wire is too thick, you’ll have to spend more money. Usually, thick wires are expensive. (2)

Wrapping Up

Whenever you choose a battery cable wire size, follow the above guidelines. It will surely help you pick the right wire size. Besides, you don’t have to depend on the chart every time. With a few calculations, you can check the acceptable voltage drop.

Take a look at some of our related articles below.




References
(1) resistance – https://www.britannica.com/technology/resistance-electronics
(2) wires are expensive – https://www.alphr.com/blogs/2011/02/08/the-most-expensive-cable-in-the-world/

Video References

Wiring Products

ChrisFix

Howcast

ArizonaHotHomestead

About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.