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How to Choose 50 Amp Wire Size [Considering 3 Factors]

It’s not just the wire size gauge that should be considered while dealing with electric projects. Several other factors also come into play along with the gauge size of the wire.   

What gauge should you use for 50 amp wire size

The correct wire size for a 50 amp circuit breaker or appliance is 6 gauge. Bigger size wire is fine. But using smaller wire could pose serious threats like overheating, melting and fire hazard. Sending electric signals at some distance might require a bigger gauge size like 4 AWG. 

Besides choosing the right gauge wire, other important factors can not be overlooked. 

I will tell you about each and every factor. Let’s dive right into it!

Factors for Choosing 50 Amp Wire Size

To suit 50 amp ampacity you will usually encounter 3 AWG standard wire gauge sizes:

  • 8 gauge wire having 50A ampacity
  • 6 gauge wire with 65A ampacity
  • 4 gauge wire with 85 ampacity

The correct gauge size for 50 amp is 6 gauge wire. But you might think 4 gauge should be the right and appropriate choice with 50 amp.  

The thing is that you are leaving out an important factor. And that factor is the 80% breaker rating rule given by the National Electric Code (NEC). 

Let’s check all the factors that must be considered!

Factor 1: NEC 80% Rule

Trying to create a 50 amp current with a 50A ampacity wire won’t work. Because it would fry the circuit. 

NEC suggests using an extra 20% on the top of 50A ampacity.  Let us calculate the ampacity for the 50 amp wire. 

Wire ampacity = 50A/0.8 = 62.5A wire (0.8 for the 80% rule set by NEC)

Well the formula says you should use 62.5 ampacity wire to be exact. But we don’t have 62.5 ampacity wire. We have either the 50A wire or the 65A wire.

Remember when we said smaller would pose serious problems like but bigger is fine. So the closest wire that we can use for 50 amps is the bigger one. Which is 65A with a 6 gauge wire size.  

And if bigger is good, then it means using 4 gauge wire for 50 amp would also work. But it may create a bit of inconvenience due to the bigger wire being heavier and stiffer. 

That is why the perfect choice for 50 amp is a 6 gauge wire with 65 ampacity. Check out how a 15 amp switch would work with a 20 amp circuit.

Factor 2: Voltage Drop 

Voltage drop is a key factor to consider when deciding gauge size for 50 amp. Simply put, you have to compensate for the 20% voltage every 100 feet. 

So, if you lose 20% voltage when distance increases, what do you do then? Of Course, avoiding the smaller, you simply choose a bigger size wire. 

Suppose, you were using 6 gauge wire for a 50 amp. And you require your device somewhere 100 feet away. While also balancing for 20 % voltage drop. 

In that case, you simply need 62.5 * 1.2 = 75 ampacity wire for a 50 amp device. But we don’t have 75A. So we will use the bigger size which is 4 AWG and can handle up to 85 ampacity. 

Remember that it does not matter if it’s 400 amp wire size that you are using. The formula of voltage drop will work the same way for every wire size. 

Check out these wires used for different distances:

DistanceWire Gauge Size (Copper)Wire Gauge Size (Aluminum)Voltage
50 Feet6 AWG4 AWG120 Volts
100 Feet4 AWG3 AWG120 Volts
50 Feet6 AWG4 AWG240 Volts
100 Feet6 AWG4 AWG240 Volts

Hope the chart will clarify about choosing the gauge size while considering voltage drop. 

To further ease you in your choice check the wire sizes of different lengths of wires:

Product 1
Product 2

I hope now you know exactly what wire you need. 

Factor 3: Choosing the Conductor

Gauge size is surely going to be different based on the type of conductor you are using. 

It is best to see what size is required for a 50 amp device with the type of conductor. 

50 Amp Aluminum Wire Gauge Size 

Aluminum wire is lighter but uses only 61% of the conductivity. And this is the reason that for a 50 amps device you use 4 AWG aluminum wires. 

Also aluminum is malleable and an ideal choice for larger distances. So why not then use aluminum over copper?

The reason is simple, copper when compared to aluminum, is an expensive choice. 

Check out the gauge chart for both the conductors. Here I have listed them using different amps on different temperature ambients: 

Wire Gauge SizeAluminum Amp-167°FAluminum Amp-194°FCopper Amp-194°FCopper Amp-167°F
8 AWG40455550
6 AWG50607565
4 AWG65759585

The ambient temperature is also important when choosing gauge size for a specific amp rating.      


Question: Does 50A wire size change with machines?

Answer: Yes wire size kind of does change with machines. For example, a 50 amp welder would require you to use 6 AWG wires. Because they run on an amperage range of 40 to 50. Likewise, an air conditioner would require 12 AWG and generate runs on 10 to 6 AWG.

Question: How do you determine wire gauge size?

Answer: To determine wire gauge size check out the insulation of the wire. You will see a few numbers printed on it. So if the wire is 6 gauge, it might be written something like this 6/2. This “6” is the gauge size while “2” is the number of conductor wires. 

Question: How to wire a 50 amp RV plug?

Answer: Disconnect any power. Now attach white wire in neutral prong. The red would go into the hot1 and black into the hot2 prong. 

And lastly you would be left with the orange\green which is for the ground prong. And remember, 4 prongs 50 amp plug is 110 volts.  


I hope that now choosing a 50 amp wire size would be easy for you. 

Remember that it’s just not the gauge number that you will consider. All the 3 factors are equally important for the choice. 

Be safe. That’s all.