What Type of Wire to Feed 100 Amp Subpanel
Looking for wire size for 100 amp service? If you are trying to set up a 100 amp conduit circuit, you will need to make sure to choose the right wire size. 100 amp circuit at 240V can handle up to 24,000W of electricity.
Power = 100 Amps × 240V = 24,000W
In the US, we have an AWG gauge system for wire sizes. These wires range from the biggest 0000 AWG wire with 230 ampacity to the smallest 40 AWG with less than 0.1 ampacity.
With 100 amps sub panel wire size, we get a number of different questions, such as:
- What size wire for 100 amp service?
- What size wire is good for 100 amps?
- What size wire for 100 amp service 100 feet or 150 feet away?
- What is the 100 amp breaker wire size?
Many homeowners use smaller #4 AWG and #2 AWG wires for 100 amp service and wonder why they fried their sub panel. To avoid frying your circuit, it's vital to account for two key factors that come into play here:
- 80% National Electric Code (NEC) requirement (NEC 220-2 Code).
- Distance from the sub panel due to the 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 is how you adequately size a wire for 100 amp service:
First, check the wire gauge chart here. You have all the AWG copper wires and their ampacities listed (at median 75°C or 167°C temperature). From that chart, you can see that we have 4 wire sizes with amps in the vicinity of 100 amps. These are:
Now, it seems that a #3 AWG wire with 100 ampacity is the perfect 100 amp wire size. That's a very common mistake. In fact, the most appropriate wire size for 100 amp service is the #1 AWG wire with a 130 amp median capacity.
To understand why this is, and what wire size you need for 100 amp sub panels 100 or 150 feet away, let's look at the what the NEC code requirements are for 100 amp wire size:
100 Amp Wire Breaker Size With 80% NEC Requirement
As you can see from the chart above, these are the wire ampacities in the vicinity of 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 is what NEC code says about 100 amp sub panel wire sizes:
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 a safety measure. You never put the circuit under 100% ampacity; at most you wire it to hit 80% ampacity. For our wires, this is what the actual ampacity is:
- #4 AWG has 85A ampacity but should conduct at most 68 amps.
- #3 AWG has 100A ampacity but should conduct at most 80 amps.
- #2 AWG has 115A ampacity but should conduct at most 92 amps.
- #1 AWG has 130A ampacity but should conduct at most 104 amps.
As we can see, the #3 AWG wire might have 100A ampacity but it 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 electric device you want to run. What is the sub panel is 100 feet away? You will need a bigger wire, and here's how you determine the 100 amp wire size for sub panel 100 feet away:
Wire Size For 100 Amp Sub Panel 100 Feet Away
With distance, inevitably the voltage in the circuit drops. This drop is insignificant at low distance (less than 3%) but at longer distances like 50, 100, or 150 feet, the voltage drop is significant enough and you will have to account for it.
To counter the 100 amp voltage drop, you have to increase the amperage. The key question here is how much you have to increase the amps to counter this voltage drop.
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 that means for a 100 amp sub panel 100 feet away (we have to account for 2 things):
- First, we need to account for 80% NEC code as we did before.
- On top of that, we need to account for this 20% voltage drop due to sending electricity 100 feet away.
Here how we determine the ampacity we need from the wire:
Account for 80% NEC code: At 0 feet distance, we need 100 amps. This 100 amps should be at most 80% of the ampacity of the wire. If 100 amps is 80%, what is the 100% wire size?
Min. Wire Ampacity = 100% × 100A / 80% = 125 Amps
If the sub panel would be 0 feet away (very close) we would need a minimum 125A wire.
Account for 100 feet away: Our sub panel is 100 feet away. That means we need to boost the amps by an additional 20%. How much does that get us?
Min. Wire Ampacity (100 ft away) = 125A × 1.2 = 150 Amps
That means that we need a wire with at least 150 ampacity to deliver 100 amp service 100 feet away. If you check the wire size chart (you have the link in the introduction), the #0 AWG wire (also known as 1/0 AWG wire) has 150 ampacity. That means that #0 AWG wire is the perfect size wire for 100 amp service 100 feet away.
Using this kind of calculation, you can pretty much determine which breaker size you need for 100 amp service at any distance. To illustrate, let's look at 150 feet distance:
Wire Size For 100 Amp Sub Panel 150 Feet Away
Alright, as we have calculated before, we need at least 125 ampacity wire to handle 100 amp current. Now we need to add the 30% amp boost (+20% per every 100 feet, hence +30% for 150 feet) to these 125 amps:
Min. Wire Ampacity (150 ft away) = 125A × 1.3 = 162.5 Amps
For sending 100 amps current 150 feet away, we need a wire with at least 162.5 ampacity. If you consult the wire gauge chart, you see that the #0 wire can handle 150 amps. It's too small.
100 amp service 150 feet away from the sub panel requires #00 AWG wire (also known as 2/0 AWG wire). This wire has a median ampacity of 175 amps; more than enough than the required minimum 162.5 ampacity.
We hope all of this helps. If you haven't found the answer to your 100 amp question, you can use the comments below and we'll try to help you out. For 100 amp aluminum wires, you can consult the aluminum AWG wire chart.
It might also be helpful to read some of our related articles on similar topics, including:
- 20 amp wire size.
- 30 amp wire size.
- 40 amp wire size.
- 50 amp wire size + sub panel at a 100 feet distance.
- 60 amp wire size + sub panel at a 100 feet distance.
- 200 amp wire size.
Source: https://learnmetrics.com/100-amp-wire-size/
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