What is the wire from the battery to the starter?

Content

Need to know factors about battery cable size
- Bearing load
- Length of cable
Permissible voltage drop for 12V battery cables
Which wire is best for battery starter cables?
F.A.Q.
- Can a small size battery cable be used?
- Can I use an oversized battery cable?
Summing up

When the connection between the car's battery and the starter is not strong enough, you may have trouble starting. It is extremely important to connect the battery and starter with the correct wire size. So, that's why today I'm going to give you some advice on what gauge of wire to use from your battery to your starter.

In general, for proper operation follow the gauges below for the correct size of the battery starter cable.

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

That's all. Now your car will receive constant power.

Let's take a look in more detail below:

Need to know factors about battery cable size

Before jumping to conclusions, you need to understand a few things. Selecting the correct wire gauge depends entirely on two factors.

Bearing load (current)
Length of cable

Bearing load

Usually the starter is capable of delivering 200-250 amps. Since the current is very large, you will need a fairly large conductor. If the cable is too thick, it will create more resistance and disrupt the flow of current.

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

A cable that is too thin can cause a short circuit. So choosing the right cable size is critical.

Length of cable

As the length of the wire increases, the resistance increases automatically. According to Ohm's law,

Therefore, the voltage drop also increases.

Permissible voltage drop for 12V battery cables

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

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

Tip: AWG, also known as American Wire Gauge, is the standard method for determining wire gauge. When the number is high, the diameter and thickness become smaller. For example, 6 AWG wire has a smaller diameter than 4 AWG wire. So a 6 AWG wire will create less resistance than a 4 AWG wire. (1)

Which wire is best for battery starter cables?

You know that the correct cable size depends on the amperage and distance. Thus, when these two factors change, the size of the wire can also change. For example, if 6 AWG wire is enough for 100 amps and 5 feet, it won't be enough for 10 feet and 150 amps.

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

What we have learned so far:

Starter = 200-250 amps (assume 200 amps)
V = IC
Allowable voltage drop for a 12V battery = 0.36V

Based on the three baseline results above, you can start testing 4 AWG wire. Also, we will use distance like 4 feet, 7 feet, 10 feet, 13 feet, etc.

Wire resistance 4 AWG per 1000 feet = 0.25 ohm (approx)

Consequently, the

At 4 feet

Click here for Wire Resistance Calculator.

Wire resistance 4 AWG = 0.001 ohm

Consequently, the

At 7 feet

Wire resistance 4 AWG = 0.00175 ohm

Consequently, the

At 10 feet

Wire resistance 4 AWG = 0.0025 ohm

Consequently, the

As you can imagine, at 10 feet, 4 AWG wire exceeds the allowable voltage drop. So, you will need a thin wire 10 feet long.

Here is the complete diagram for distance and current.

Current (Amp)	4ft	7 feet	10 feet	13 feet	16 feet	19 feet	22 feet
0-20	12	12	12	12	10	10	10
20-35	12	10	10	10	10	8	8
35-50	10	10	10	8	8	8	6 or 4
50-65	10	10	8	8	6 or 4	6 or 4	4
65-85	10	8	8	6 or 4	4	4	4
85-105	8	8	6 or 4	4	4	4	4
105-125	8	8	6 or 4	4	4	4	2
125-150	8	6 or 4	4	4	2	2	2
150-200	6 or 4	4	4	2	2	1/0	1/0
200-250	4	4	2	2	1/0	1/0	1/0
250-300	4	2	2	1/0	1/0	1/0	2/0

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

F.A.Q.

Can a small size battery cable be used?

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

Can I use an oversized battery cable?

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

Summing up

Whenever you choose the size of the battery cable wire, follow the guidelines above. This will definitely help you choose the correct wire size. Plus, you don't have to rely on the chart every time. By doing a few calculations, you can check the allowable voltage drop.

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