50 amp is one of the most common amperages we need a gauge, breaker, or a wire for. The key questions regarding the 50 amp wire include:
- What is a wire size for 50 amps 240 volts? (50 amp wire gauge; NEC code applies)
- Wire size for 50 amp sub panel 100 feet away? (Here we will have to account for voltage loss)
- What electric devices can you run with a 50 amp wire? (Wattage will depend on voltage)
Let’s first clear the AWG wire gauge size:
If you check the wire gauge ampacity chart here, you can see that there are 3 AWG wire sizes that have ampacity near 50 amps. These are:
- 8 AWG wire with 50A ampacity (too small).
- 6 AWG wire with 65A ampacity (just right).
- 4 AWG wire with 85A ampacity (too big).
Now, choosing the 8 AWG wire with 50A ampacity seems like a good choice as a 50 amp wire size, right? However, in almost all cases, the correct 50 amp wire size is 6 AWG with 65A ampacity. That is true for any voltage; 12V, 110V, 115V, 120V, 220V, 240V, you name it.
Why is that?
We have to account for the 80% breaker rating rule, set by National Electrical Code (NEC) rules. Maximum loading for any branch circuit is 80% of the rating of the circuit for ampacity of wire for any load.
Let’s have a quick look at how you can choose the right AWG gauge wire for 50 amps (or any amps for that matter). Later on, we will also look at when 6 AWG wire is not adequate as a 50 amp wire (due to voltage loss at a distance), and what you can run with a 50 amp 110V or 220/240V circuit:
50 Amp Wire Size (Using NEC 80% Rule)
You can’t use 50A ampacity wire to create a 50 amp electric circuit. If you do that, you will likely fry the circuit.
The 80% rule serves as a safety measure. You should at least have that extra 20% on top of 50A ampacity.
Here is how you calculate at least how much ampacity should a 50 amp wire have:
Wire Ampacity For 50 Amps = 50A / 0.8 = 62.5A Wire
That means that you should use a wire that can handle 62.5A as a 50 amps wire. Now, we don’t have 62.5A wire. The closest wire we have is the 6 AWG wire with 65A ampacity.
Note: You can always use a bigger wire but never a smaller wire. For 50 amps, you could use 4 AWG wire with 85A ampacity (a bit of overkill but it’s OK), but you can never use 8 AWG wire with 50A ampacity (you will fry the circuit).
In most cases, 6 AWG is an almost perfectly-sized wire for a 50 amp breaker. In limited cases, you will probably have to use a larger 4 AWG wire. That’s when you have a long circuit and are sending electrical current at some distance (100 feet or more).
50 Amp Wire Size 100+ Feet Away (Account For Voltage Drop)
Even you’re sending electricity through a long distance (for example, to a 50 amp sub panel 100 feet away), you have to account for voltage drop.
A good rule of thumb for voltage drop is this:
For every 100 feet, voltage drops by 20%.
In order to get the same wattage (power) at the sub panel 100 feet away, you have to increase the amps by 20% (to balance out the 20% drop in voltage).
That, of course, means that you are dealing with more current (more amperes) and you have to choose a bigger-sized wire.
Example: 50 amp wire is usually the 6 AWG (we require at least 62.5A and 6 AWG can handle 65A). If you have to power an electric device 100 feet away, you need 20% amps more. Instead of 62.5A, you’re looking at 62.5A × 1.2 = 75A.
In this case, the 6 AWG gauge wire with 65A will not be enough. We need at least 75A. The next wire size that can handle more than 75A is the 4 AWG gauge wire. This one can handle at 85A and is usually used as a 50 amp wire size for 100 feet away sub panels.
There are quite a lot of questions regarding 50 amp and different voltages. Let’s tackle this one as well:
What Size Wire Do I Need For 50 Amp At 110-240V?
A common misconception regarding 50 amp wire is that we need different wire sizes for different voltages. We don’t need a bigger (or smaller) wire size for 50 amp at 240V than for 50 amp at 110V, for example.
In all cases (with the exception when we have to account for voltage loss) we use 6 AWG wire for 50 amps.
Now, the wire size and the amps might be the same. With different voltages, we don’t get different amps; we get different power (wattage).
What gauge wire for 50 amp 220V?
For example, a 50 amp wire on a 220-volt circuit (you will need a 6 AWG wire) can handle up to 11,000W of power (this is a very common electricity setting for RVs). Here is how you can calculate that:
Wattage = Amps × Volts = 50A × 220V = 11,000W
If you have a 110V circuit, the 50 amps will produce 5,500W of power.
We hope the topic of 50 amp wire sizes is a bit more clear now. You can also check out a similar post for:
Awesome article.
You may be referencing a regular home or business, but this information transfers very well to those of us who own motor coaches. When we connect to shore power, it is usually 50 amp service and our power cord (35 foot) on our coach is 4 AWG. I purchased a 25-foot extension which is also 4 AWG.
Hello Mike, yes, 4 AWG is a smart choice for 50 amp service. You don’t run into the risk of trying the wire.
I live in an R.V. Park. PGE provides electricity that is fed through a master meter before it is fed to the individual sights. All 90 campsites have individual meters.
5 or 6 years ago the park added 50 service to all of the sights. When back filling the trenches that were dug the bucket of the back hoe made contact with one of the hot legs scraping off the insulation on the aluminum cable and exposing about 18 inches to the ground. This damage went unoticed and was only recently repaired. Before the repair the outlet at my camp site measured 119 volts on one leg and 80 volts on the second leg. Accross both legs it measured 200 volts.
The short to ground was after the master meter PGE uses to billl the park and before the meter at my campsite. that determines my usage. Question: The Short to ground caused the loss of 40 volts
Did the park get charged by PGE for the 40 volts that were lost ?
Tom
Hello Thomas, that’s quite an unfortunate event. We here try to advise everybody with the HVAC calculations but we don’t have adequate knowledge how to talk to the park about this matter. Hopefully, you’re successful in resolving this.
The answer is no. The voltage drop was due to grounding. There was no load therefore no usage of the energy. Your potential was the thing affected
If there is a voltage drop, there is a load, even if the load is the 500 feet of conductor itself. The question is whether the meter measured that load. Since the Neutral is bonded to the ground at the first panel, and after the meter, then, yes, the meter would measure the load and record usage.
If I took a 40W bulb and mis-wired it in my house so that it has a live in and a ground out, my meter will record a 40Ah usage. In your particular case, the load is the soil between the exposed ground, and the exposed live.
If the ground wire was not bare, and not exposed, then the load will be the soil between the exposed live, and the ground rod at the first panel.
The answer is yes, the park main meter would have been charged foe the usage…aka Loss to the grounding…
Your electrical appliances was under stress not having the sufficient voltage to run properly. This causes premature wear on electrical components and motors. That being said, it was affecting all that was on that one leg, or both legs.
Hey. Running a 50amp circuit for camper. Using #6 , what size neutral and ground wire.
Hi Sam, ground wire size is found in NEC Table 250.66. We include that table in our article about ground wire sizing here.
Here is the short summary: If you have a #6 hot copper wire, you need a #8 ground copper wire. If you have a #6 hot aluminum wire, you need a #6 AWG ground aluminum wire. Same for neutral wires. Hope this helps.