200 amp wires are quite big. They can be used as 200 amp ground wires, wires for 200 amp breaker, they can be copper or aluminum 200 amp wires. The common question for all these applications here is this:
What size wire do I need for 200 amp service?
If you look at the AWG gauge wire chart here, the answer seems to be quite clear (it’s not that simple, however):
As you can see, the obvious – but wrong – the choice is using a #000 AWG wire for 200 amp service (also known as 3/0 AWG) because it has a 200A ampacity. That, however, will likely end with you frying the wire.
For safety measures (in order to avoid frying a 200 amp circuit), the National Electric Code (NEC) dictates the following requirement:
Maximum loading for any branch circuit is 80% of the rating of the circuit for ampacity of wire for any load. (NEC 220-2)
This is known as NEC 80% requirement for wire sizing. In the case of 200 amps breakers, this means you will need a wire with at least 250A ampacity to connect a 200 amp service.
Looking at the AWG wire chart, you will need an even bigger than #0000 AWG wire for 200 amps. You have to go beyond the AWG chart at look at the KCMIL wire chart.
KCMIL wires are bigger and can handle currents of 200 amps and higher. Here is a shortlist of KCMIL wires that can be used for 200 amps:
- 250 KCMIL wire with 255A amperage.
- 300 KCMIL wire with 285A amperage.
- 350 KCMIL wire with 310A amperage.
- 400 KCMIL wire with 355A amperage.
- 500 KCMIL wire with 380A amperage.
The 250 KCMIL wire is the perfect size wire for 200 amp service because it has 255A ampacity (a minimum of 250A ampacity requirement is satisfied).
We will show you how this 250A ampacity is calculated. On top of that, you will also need a bigger wire gauge if you want to send electricity 100 feet or 150 feet away from sub panel (we will show you how to calculate what size wire you need in this case as well).
200 Amp Wire Gauge Calculation: What Size Wire You Need For 200 Amp Circuit?
To adequately determine the 200 amp wire gauge, you first need to calculate the minimum ampacity requirement as per the 80% NEC rule.
In the case of the 200 amp circuit, here is how the calculation looks like (you have to leave 20% extra amps capacity for safety reasons):
200 Amp Wire = 200A × 100% / 80% = 250A Ampacity
That means that you can to use a wire that has an ampacity of 250A or higher in order to set up a 200 amp circuit.
As you can see from the list of KMCIL wires above, the 250 KCMIL wire is perfect for a 200 amp service since it has an ampacity of 255A.
Now, if the sub panel is some distance away (50 feet, 100 feet, 150 feet, 200 feet, and so on), you will probably have to use an even bigger wire to counted the voltage drop.
The NEC 310-16 requirements cover this nicely:
How To Account For Sub Panel Being 100 Feet Away?
When sending electricity a long way from the sub panel, the voltage will drop with the distance. To counter this drop, you have to boost the initial amps. That means that the circuit has to handle more amps; in turn, the wire you’re using has to handle more amps.
How much more exactly?
Roughly speaking, the NEC 310-16 requirement states that for a 200 amp copper or aluminum wire, you have to add 20% to the total amps for every 100 feet of distance.
Example: Let’s say you want to use 200 amp service 100 feet away from the sub panel. We already know that such a circuit will require wires with at least 250A ampacity. On top of this, we have to increase the amps by 20% to get the true size wire for 200 amps at such a distance:
200 Amp Wire (100 ft away) = 250A × 1.2 = 300A Ampacity
Now we have to find a wire with 300A ampacity or more. If you consult the KCMIL list above, you can see that the 350 KCMIL wire is perfect for 200 amp service 100 feet away. That’s because it has a 310A ampacity.
You can make a similar calculation for 50 feet (10% addition), 150 feet (30% addition), and 200 feet (40% addition), and choose the corresponding KCMIL wire.
Hopefully, now the 200 amp wire sizing is a bit clearer.
You should also look into different amp wires and similar calculations for:
- 20 amp gauge size.
- 30 amp gauge size.
- 40 amp gauge size.
- 50 amp gauge size.
- 60 amp gauge size.
- 100 amp gauge size.
If anything is unclear, you can use the comments to pose a question and we’ll try to help you out.
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When sizing wire for a sub panel, do I use the total amperage of the sub panel or the expected maximum load? In my case, I want to install a 200 amp sub panel in an out building that will be used for a home auto / wood working shop. I can’t visualize ever drawing more than 60 amps but for safety margin let’s assume it is 100 amps. Do I size my wire for the full 200 amps or the 100 amps? This panel is 200′ from my main panel.
Hello George, you will need to be aware of the voltage drop here. You are trying to think of the expected maximum load. For example, if you need 100 amps at the end of the wire, you might want a wire that can handle at least 200 amps.
Wire size for 200’ with 200 amp at end of wire coming from meter to house?
Hello Chace, if we presume a linear voltage drop, and 100′ incurs a 20% drop, we are dealing with a 40% drop if the wire length is 200′. You need a minimum ampacity of 250A (accounting for the NEC 80% rule). Here’s how you calculate that: 250A*1.4 = 350A. So, you need a wire with 350A ampacity. That’s a massive amount of amps, by the way.
So massive that even if you consult this AWG wire size chart, you will see that no single wire has a 350A of higher ampacity (the biggest 4/0 AWG wire has 230A ampacity). That means you will have to either use several wires in one cable or a bigger kcmil wires. The best solution here is to get that big 400 kcmil copper wire; it has a 355A ampacity at 75°C. Hope this helps a bit.
Hello,
I need to run wire from my main breaker panel to my shop. I have 200amp service at the main panel in the house and plan on using a 100amp (prefer 125amp) breaker in that panel to service the shop. The distance is 220′ (probably actually just a few feet less) and will be run in underground conduit. It’s confusing but would 2/0 work for that amperage and distance? Thanks.
Hello Roger, the 2/0 AWG copper wire has an ampacity of 175A at 75°C. With a 125A breaker, the 2/0 AWG is the right size wire in this situation.
At 125 feet I need to use 4/0 Al for a 100 amp sub panel. Will that panel take the 4/0 or do I need a higher amp sub panel?
Hello Chuck, for a 125 feet 200A service you would need a wire with at least 360A ampacity. 4/0 aluminum wire has a median ampacity of 180A. So that would be too small. You can use two 4/0 wires for a combined ampacity of 360A. You can use a single 700 KCMIL wire with 375A ampacity as well.
I have a 200 amp metered panel. I have a garage 240′ away with a 200 amp panel.
I want to send 125 amps to garage. For a run that long, what would be the appropriate wire size? I plan to use aluminum.
Note: I have an electrician that I am working with and that will do the work. Building a house. PGE is installing power soon. Trying to decide on placement of customer power pole. It’s about 500 feet from house to garage. I am considering “splitting the difference”, placing pole roughly 250 spot from each location.
Hello Micheal, 240 feet is quite a long way. The linear relationship of ‘20% drop per 100 ft’ might not apply at such long distances. You should consult with your electrician about the size of a 200 amp wire for 200 feet away or more.
Nonetheless, we can still apply this rule. That means that the drop would be about 48% if the garage is 240 feet away. Now, you want to send 125 amps, and we have to account for the 80% NEC rule as well. Here is a bit of how the calculation would go: 125A/0.52 = 240A. Now you multiply by 1.25 factor to account for 80% NEC rule, resulting in 300A. So, you are looking for an aluminum wire with 300A ampacity at a median 75°C temperature. You can consult this kcmil wire size chart here to find the wire; specifically, you would need a 500 kcmil aluminum wire with 310A ampacity. Hope this helps.