How to Choose Wire Size for 50 Amp Car Charger?

Wire size is a critical factor for any home car charger. It not only impacts the rate and efficiency of the charging process, but a poorly chosen charging wire can pose an electrical hazard.

This article will thoroughly guide you about choosing the wire size for 50 amp car charger.

So, without further ado, let’s get started!

What is the Perfect Wire Size for a 50 Amp Car Charger?

In light of the National Electrical Code (NEC) 80% rule and accounting for 10% voltage drop and line losses, 6 AWG and 75 amps ampacity wire size will be perfect. Or you can also choose 4 AWG and 70 amp ampacity wire.

NEC’s 80% rule states that current passing through a wire should not exceed 80% of its current carrying capacity. So, for a 50 amp charger, that would come to 62.5 amps. If one has to account for line losses and voltage drop, then increase this number further by 10%, which is 68.75A.

Now, if you search the AWG vs. Ampacity tables, you will find that 4 and 6 AWG might be the most suitable options for our current ratings. But I would recommend going for 6 AWG and 75A ampacity wire for ease of installation and cost reduction.

Another variable in the AWG charts is the current rating at a given temperature. So, if we’re choosing a thin wire of 6 AWG, we choose one with the highest temperature resistance.

Wire material is as important as its size. It is highly recommended that you use high-quality copper wires. All the variables discussed though this article will be for copper wires. One can choose an aluminum or silver wire but would need a thicker wire to hold the same amount of current.

Why is it Important to Choose the Correct Wire Size for a Car Charger?

For an efficient and safe EV charging process, choosing a car charger with the correct wire size is pertinent. If the wire size of your car charger is too small, it can melt and burn down. A thick wire may be expensive to buy and difficult to install.

In any electrical application, choosing a wire with the correct size is important. EV charging cables are no different. You must know that car chargers come in all sizes and power ratings. A regular charging cable allows passage to 3-9 kW of electrical power.

On the other hand, a fast charging cable transmits 10-40 kW of power. Fast charging cables are a key to quick EV charging at home. DC fast chargers can provide up to 350 kW of electrical power to your vehicle, but that is a topic for another day.

Right now, I’m explaining the importance of choosing the correct wire size for a home-based car charger. Here, the design of the charging system is your prerogative. An important specification in choosing a wire is its size or gauge, otherwise known as American Wire Gauge (AWG).

A higher gauge means a thinner wire, whereas a lower gauge means a thicker wire. It is recommended to use a low gauge wire for fast charging, while for regular charging, a higher gauge wire would do. I’ll elaborate on this statement in the next sections.

Important: EV battery replacement can cost $1000s. To avoid high-voltage battery replacement, there are some things you can do. Read this article to find out the 10 best ways to maximize EV battery life and save tons of money!

Why Can’t You Choose 50A Ampacity Wire for a 50 Amp Car Charger?

The National Electric Code (NEC) states that no more than 80% of the designated current rating should pass through any wire of an electrical circuit. Along with this, many factors, such as line losses, voltage drop, and charger length, are at play here. Due to these reasons, you can’t simply choose a 50A ampacity wire for a 50 amp car charger.

Choosing the wire size for a car charger is a subjective matter. You must decide the wire size based on a given set of conditions and desired output. However, a few rules are universal. One is mentioned in the National Electric Code (NEC), which is used as a standard guidebook for all electrical tasks in North America.

According to the 80% rule, the current passing through a wire should not exceed 80% of its current carrying capacity. If you follow this rule, then a 50A ampacity wire should not be used for a car charger above 40A.

Also read: EV Battery in Hot Temperature: 5 Things to Know

How Do You Calculate the Lines Losses in a 50 Amp Car Charger?

You can calculate the line losses in a 50 amp car charger by squaring the current rating, which is 50 in this case, and multiplying it by the length of the wire, constant resistance for that particular gauge, and the time taken to fully charge your car.


Line Losses (kWh) = [(Current)^2 x (Wire Length x Constant Resistance x Charging Time)]/1,000,000

Let’s consider a case of a 50 amp charger with 6 AWG wires. The resistance constant for a 6 AWG wire is 1.296 m Ω/m. The length of the charger is 8 meters, and it takes 6 hours to fully charge. Then the lines losses would come out to be:

[(50 A)^2 x (8 m x 1.296 m Ω/m) x 6 hours]/1,000,000 = 0.1552 kWh

If your car has a battery pack of 66 kWh and is charged at 220V and 50A, nearly 0.3% of the total power will be lost during transmission through the wire. In the case of a thicker wire, say 3 or 4 gauge, these line losses can become more significant.

Line losses must be accounted for when choosing your car charger’s wire size. A thicker wire will have higher losses than a thin wire. Line loss is the amount of power lost due to the resistance of the wires and other components in the charging system. This causes some of the electrical energy to be converted into heat and dissipated into the environment.

Does Wire Size Affect the Speed of EV Charging?

Yes, wire size can affect the speed of EV charging. A high gauge (thin) wire cannot hold the large amounts of current required to quickly recharge your car’s battery pack. This can lead to voltage drops and heat losses.

I’ve been saying that wire size is too important to ignore. All EV owners must educate themselves on choosing the correct wire size for any car charger. Now, charging speed is a critical factor. Suppose you invested $2,000 in a home fast charging station. What good will it do if the wire cannot support and transmit increased current levels?

Does Voltage Affect the Wire Size of a 50 Amp Car Charger?

Not really. The wire size of a 50 amp car charger isn’t affected by voltage ratings. Voltage is just a driving force. Electrical current is actually flowing through the wire in the form of electrons. You only got to worry about the current rating while choosing wire size.

Consider that you have an 11.2 kW onboard charger in your EV. If the voltage at your home is 110V, then the 50 amp charger will draw the maximum current at this voltage to bring power up to 5.5 kW. The power wouldn’t go up until you get a charger with a high amp rating.

While if the voltage at your home is 240V, then the 50 amp charger will draw 46.67 amps from the mains to bring the total power up to 11.2 kW. So, you see. Current is the limiting factor in electrical applications, not the voltage.

What Will Happen if You Don’t Choose the Correct Wire Size for a 50 Amp Car Charger?

Choosing the incorrect wire size for a 50 amp car charger poses a grave safety threat. In case of a wiring meltdown or a short circuit, you risk burning down the entire electrical wiring of your house. Plus, damage to car charging infrastructure is a possibility.

Choosing the correct wire size for a 50 amp car charger is very important. Things might not be that serious for a car charger with lower current ratings. But 50 amps is some amount of current. So, if you’re ever in doubt, consult an expert electrician that deals in car charging systems.

I hope this article was helpful in choosing the correct wire size for a 50 amp car charger. Please share your thoughts in the comments below.