Looking for wire sizes for 100 amp service? If you are trying to install a 100 amp drain circuit, you need to be sure to choose the correct wire size. At 240V a 100 amp circuit can handle up to 2,200W of power.
power = 100 amps × 240V = 2,400W
In the US, we have an AWG gauge system for wire sizes. These wires range from the largest 0000 AWG wire with 230 ampacity to the smallest 40 AWG with less than 0.1 ampacity.
With 100 ampere sub panel wire sizes, we get many different questions, such as:
- What size wire for 100 amp service?
- What size wire for 100 amp service 100 feet or 150 feet away?
- What is the size of 100 amp breaker wire?
Many homeowners use shorter #4 AWG and #2 AWG wires for 100 amp service and wonder why they fried their sub panels. To avoid frying your circuit, it’s important to keep two key factors in mind at work here:
- 80% National Electric Code (NEC) requirement (NEC 220-2 code).
- Distance from sub panel due to voltage drop (NEC 310-16 code).
We will use both of these factors when determining what size wire you need for 100 amp service.
Here’s how you size a wire large enough for 100 amp service:
First, look at the wire gauge chart here. You have all the AWG copper wires and their ampacity listed (average at 75°C or 167°C temperature). From that chart, you can see that we have 4 wire sizes with amps around 100 amps. These are:
Now, it looks like a #3 AWG wire with 100 amps is the correct 100 amp wire size. This is a very common mistake. In fact, the most appropriate wire size for 100 amp service is #1 AWG wire with 130 amp average capacity.
To understand why this is so, and what wire size you need for a 100 amp sub panel 100 or 150 feet away, let’s look at the NEC code requirements for 100 amp wire sizes:
100 Ampere Wire Breaker Size With 80% NEC Requirement
As you can see from the chart above, these are wire amps around 100 amps:
- #4 AWG can handle 85 amps.
- #3 AWG can handle 100 amps.
- #2 AWG can handle 115 amps.
- #1 AWG can handle 130 amps.
Here’s what the NEC code says about 100 amp sub panel wire sizes:
The maximum loading for any branch circuit is 80% of the circuit’s rating for the wire’s capacitance for any given load. (NEC 220-2)
This is a security measure. You never put the circuit under 100% ampacity; At most you wire it to hit 80% ampacity. For our strings, this is the actual ampacity:
- #4 AWG has 85A ampacity but should operate at a maximum of 68 amps.
- #3 AWG has 100A ampacity, but should operate at a maximum of 80 amps.
- #2 AWG has 115A ampacity but should operate at a maximum of 92 amps.
- #1 AWG Has a Width Of 130A But Must Conduct max 104 amps,
As we can see, #3 AWG wire can have 100A ampacity but should only be used in circuits that require 80 amps or less.
With the 80% NEC rule, the best wire size for 100 amp service is #1 AWG.
Now, this is the correct wire size for a sub panel that is close to the electrical device you want to run. What is the sub panel 100 feet away? You’ll need a bigger wire, and here’s how you determine the size of a 100 amp wire for a sub panel 100 feet away:
Wire size for 100 amp sub panel 100 feet away
With distance, inevitably the voltage in the circuit drops. Over short distances (less than 3%) this drop is negligible, but over longer distances like 50, 100, or 150 feet, the voltage drop is significant and you have to account for it.
To counteract the 100 amp voltage drop, you have to increase the amperage. The important question here is how much do you have to increase the amps to counteract this voltage drop.
The NEC 310-16 rule tells us that, roughly speaking, we need to increase the amps by 20% for every 100 feet of distance from the sub panel.
Here’s what this means for a 100 amp sub panel 100 feet away (we have to account for 2 things):
- First, we have to account for 80% of the NEC code as before.
- On top of that, we have to account for this 20% voltage drop due to power being sent 100 feet away.
Here’s how we determine how much we need from the wire:
Accounts for 80% of NEC codes: At 0 feet, we need 100 amps. This should be at a maximum of 80% ampacity of the 100 amp wire. If 100 amps is 80%, what is the size of the 100% wire?
the minimum. Wire Ampacity = 100% × 100A / 80% = 125 amps
If the sub panel will be 0 feet away (very close) we will need at least 125A wire.
Account 100 Feet Away: Our sub panel is 100 feet away. This means we need to increase the amps by an additional 20%. How much do we get from this?
the minimum. Wire Ampacity (100 ft away) = 125A × 1.2 = 150 amps
This means we need a wire with at least 150 ampacity to deliver 100 amp service 100 feet away. If you check the wire size chart (the link you have in the introduction), #0 AWG wire (also known as 1/0 AWG wire) has 150 ampacity. This means that #0 AWG wire is the perfect size wire for 100 amp service 100 feet away.
Using a calculation like this, you can pretty much determine what breaker size you need for 100 amp service at any given distance. For example, let’s look at a distance of 150 feet:
Wire size for 150 amp sub panel 100 feet away
Well, as we have calculated earlier, we need at least 125 ampacity wire to handle 100 amp current. Now we need to add 30% amp boost (+20% every 100 feet, so +30% for 150 feet) to these 125 amps:
the minimum. Wire Ampacity (150 ft away) = 125A × 1.3 = 162.5 amps
To send 100 amps 150 feet away, we need a wire with at least 162.5 amps. If you consult the wire gauge chart, you see that the #0 wire can handle 150 amps. It is too short.
100 amp service 150 feet away from the sub panel requires #00 AWG wire (also known as 2/0 AWG wire). This wire has an average capacitance of 175 amps; More than enough from the required minimum 162.5 ampacity.
We hope this all helps. If you haven’t found an answer to your 100 amp question, you can use the comments below and we’ll try to help. For 100 amp aluminum wires, you can consult the aluminum AWG wire chart.
It may also be helpful to read some of our related articles on similar topics, including: