10/2 Or 10/3 Wire For Air Conditioner: Why 10/3 Is A Stupid Idea?

All air conditioners have to be wired. Of course, you will have to use adequately sized wires. In the case of AC units, we most commonly think of 10/2 and 10/3 wires. That’s why we encounter many 10/2 vs 10/3 wire for air conditioners dilemmas. In actually, this is not a dilemma at all.

The trick here is to use the correct size wire that can handle enough amps (electric current). Inevitably, many homeowners come across this specific question:

“Should I use 10/2 or 10/3 wire for the air conditioner?”

Here’s the short answer: 10/2 for the air conditioner. Always? Yes, always.

Let’s explain this:

In theory, all air conditioner wiring depends on:

• Size of your air conditioner. Example: In theory, a 6-ton AC unit powered by 6,000W will require a 10/3 wire, and a 1-ton AC unit powered by 1,000W requires a 10/2 wire. But that’s just in theory. If you check the amp draw calculated below and packed into a neat chart, you will see why we don’t have to use a bigger 10/3 wire.
• Voltage. Volts and amps have an inverted relationship; the more volts you have, the fewer amps you will require for the same wattage. Example: Let’s say that a 2-ton AC unit is powered by about 2,400W. If you use the standard 120V circuit, you will need a wire that can handle at least 20 amps. If you use a 220V voltage, however, your wire will need to handle 10.9 amps.

Difference Between 10/2 And 10/3 Wire

First of all, we have to understand what we are talking about. That number ’10’ denotes that we are using 10 AWG gauge wires. The difference between 10/2 vs 10/3 is just that:

• 10/2 uses two 10 AWG wires. They have a combined ampacity of 70 amps. The wire contains one 10 gauge hot wire (black insulation), one 10 gauge neutral wire (white insulation), and an additional ground wire (for safety reasons).
• 10/3 use three 10 AWG wires. They have a combined ampacity of 105 amps. The wire contains two 10 gauge hot wire (black insulation), one 10 gauge neutral wire (white insulation), and an additional ground wire (for safety reasons).

Now, the key with air conditioner wiring is ampacity. A copper 10 AWG wire has a 35A ampacity at 75°C. After we implement the NEC 80% rule (described below) this wire can be used to conduct 28 amps of electric current. You can read more about this National Electricity Code rule and the size of wires air conditioners need here.

Now, we can calculate how many amps can both wires handle:

• 10/2 wire can handle 56 amps.
• 10/3 wire can handle 84 amps.

This means that if our air conditioner draws 50 amps, we can use both 10/2 or 10/3 wire. Of course, looking at the amps 10/2 wire can handle vs the amps 10/3 wire can handle, we can quickly see using a 10/3 wire for an air conditioner is overkill.

Theoretically, if we had an air conditioner that would draw 65 amps, we couldn’t use 10/2 wire (since it can handle only 56 amps). We will have to use a 10/3 wire.

Here’s why we never use a 10/3 wire for an air conditioner:

No air conditioner on the planet has an amp draw of more than 56 amps.

You can check how many amps air conditioners draw here. To illustrate this perfectly, we have calculated the max. amp draw air conditioners and packed them in this neat table:

Why We Don’t Use 10/3 Wire Instead Of 10/2 Wire For AC Units

Here are calculated amp draws for the 220V circuit (for 1.5-ton units and above, we always use the upgraded 220V circuit, never the 120V circuit):

As you can see, even the big 6-ton AC (10 EER rating) draws only 34.09 amps and requires wires with a minimum of 42.61A ampacity.

Well, a 10/2 already has a 70A ampacity and can allow for a 56 amp draw. Anything above that – something like a 10/3 wire – is simply overkill.

This is why we always use a 10/2 wire instead of a 10/3 wire for air conditioners.

Hopefully, this clears up this ‘dilemma’. If you have any questions regarding this, you can use the comment section below and we can discuss things a bit.