What happens when you connect a 12-gauge wire to a 15A circuit? What about 20A and 30A circuits?
Can You Put 12 Gauge Wire On A 15A Circuit? You can use 12 gauge wire on a 15A circuit. 12-gauge conductors can accommodate as much as 20 amps of electricity. 15A circuits are not a threat to them.
Most laypeople encounter this question because most homes use 15A and 20A circuits.
In other words, contractors are always asking them to choose between 14AWG and 12AWG. You would expect the contractor to make this decision. And indeed, the contractor will make a recommendation. But the layperson has the final say because 12-gauge lines are more expensive than their 14AWG counterparts.
If you leave this decision in the electrician’s hands, they will choose 12AWG. Copper Development Association Inc. performed a study in which they asked electricians to choose between these two gauges.
85 percent showed a preference for 12AWG. They highlighted the numerous benefits 12-gauge wiring brought to the table, including fewer overheating concerns, the ability to accommodate more outlets, and a lower voltage drop. Experienced laypeople usually agree with this assessment.
How To Determine Whether I Can Run 12 Gauge Wire Or Not?
You don’t have to make this decision. The NEC’s charts will choose for you. Look at the table. It shows you the various amp ratings and their corresponding wire sizes.
These are the minimum wire sizes. For instance, 8-gauge wiring can accommodate 40 amps. But that doesn’t mean you must use 8AWG for a 40A circuit. 8AWG is the smallest gauge at your disposal. Any wire size larger than 8AWG is also acceptable.
What does this mean for 15A circuits? Check the table and look for 15 amps. The minimum wire size for 15A is 14AWG. What about 12AWG? It can withstand 20A. What does this mean for you?
Technically speaking, you can use either gauge. But the temperature rating and material matter. For instance:
- 14-gauge wiring can only withstand 15A at 60 degrees C. At 75 degrees C, the amperage jumps to 20 amps. At 90 degrees C, 14-gauge conductors can transmit as much as 25 amps. That means you can’t rule out 14AWG on a 20A circuit.
- 12AWG has superior conductivity because it transmits 25A at 60 degrees C. That number spikes to 30A at 90 degrees C.
How does this help you? From this information, you can see that both options can comfortably accommodate the needs of a 15A circuit. So which one should you choose? 12AWG comes out on top for several reasons:
- 14AWG doesn’t offer an aluminum option. 14AWG aluminum is not fit for a 15A circuit. This doesn’t sound like a bad thing. According to a study from the International Journal Of Advanced Research, copper cables have superior electrical and thermal conductivity. Why would any contractor want aluminum cabling for their 15A circuit? Because aluminum is cheaper. If you prefer aluminum to copper, you can’t use 14AWG. 12AWG is the only option.
- In the event of a short circuit or surge, 12AWG is less likely to overheat because it can accommodate 20 or more amps. If you select 14AWG, the breaker will trip once the current exceeds 15 amps. 12AWG gives you five additional amps of breathing room.
- You can upgrade your circuit size without changing the wiring.
What About 12 Gauge Wire On A 20 Amp Circuit?
You can pair 12-gauge wiring with 20A circuits and breakers. Every wire size/ampacity chart you check will tell you the same thing. While 12AWG can run a 15A circuit, most contractors use it to accommodate the needs of 20A circuits.
But if you have safety concerns, you can jump up by one wire size. 10AWG gives you more room to breathe. A short circuit or surge on a 20A circuit is less likely to start a fire if the wires are 10AWG.
Even though 14-gauge wiring can withstand 25 amps at 90 degrees C, you shouldn’t connect this wire size to a 20A circuit unless you consult a licensed contractor that can select a 14AWG cable that fits the demands of your situation. 14AWG introduces fire and electrocution hazards. Don’t be surprised if an inspector penalizes you.
What About 12 Gauge On A 30 Amp Circuit?
You can’t use 12-gauge wiring on a 30-amp circuit. You need at least 10AWG. A wire size/ampacity chart will tell you the same thing. You can see that 10AWG can withstand anywhere between 30 and 40 amps, depending on the wire type and temperature rating.
Interestingly enough, this Iowa State University guide associates 10-gauge copper wires with 40 amps, even though the average contractor would ask you to use 8AWG for 40 amps. If 10AWG can work with 40A, then surely 12AWG can also accommodate 30A.
That rationale is not wrong. Wire size/ampacity charts and tables have shown that 12AWG can technically tolerate 30A at 90 degrees C. But this should only compel you to deploy 12AWG on a 30A circuit if you have an emergency and 10AWG is unavailable.
If the cable is not too long and you limit the size of the load, you can gamble with 12-gauge wiring for 30 amps. But you need to keep the risks in mind. The chances of 12-gauge conductors overheating are pretty high.
Don’t take any chances with this wire size unless you have a skilled contractor on hand to minimize the risks by selecting the correct material, wire type, length, and temperature rating for your scenario.
How Far Can You Run 12 Gauge Wire On A 15, 20, And 30 Amp Circuit?
- 15 Amp Circuit – 69 feet
- 20 Amp Circuit – 52 feet
- 30 Amp Circuit – O feet
Don’t use 12AWG on a 30-amp circuit, regardless of the length. The practice is too dangerous. Don’t forget that resistance and distance go hand in hand. A longer distance equates to higher resistance, and vice versa.
Therefore, you should aim for shorter distances to reduce the voltage drop and risks of overheating. Otherwise, you must purchase wiring with a higher gauge to compensate for the distance.
How many Outlets Can You Run On 12 Gauge Wire?
You can run as many outlets as you want. You should keep two significant considerations in mind:
- You base the number of outlets on the amperage, not the wire gauge. For instance, it is common practice to assign 1.5 amps to each outlet. Therefore, you can add 8 outlets to a 15-amp circuit if you account for the 80 percent rule.
- Most electric codes do not limit the number of outlets you can install on a circuit. They expect you to apply common sense.
With that in mind, you should also remember that the number of outlets is irrelevant. The wattage of the appliances you want to run is far more important. For instance, you can add 100 outlets to a 15A circuit if the total amps of the devices connected to those outlets are less than 15 amps.
On the other hand, one outlet accommodating a single refrigerator whose ampacity exceeds 15 amps will overload your 15A circuit, causing the breaker to trip. Admittedly, 12-gauge wiring is the safer selection in such a scenario. Even if the breaker fails to trip, the 12-gauge conductors are unlikely to overheat and melt because they can withstand more than 15 amps.
But all in all, the wire size doesn’t determine the number of outlets you can run. The amperage is the deciding variable.
Pros Of Using 12 Gauge Wire On 15 Amp Circuit
14AWG is the correct wire size for a 15A circuit. However, many contractors prefer 12AWG because it has the following advantages:
- 12AWG is thicker than 14AWG. Therefore, it can tolerate more amps.
- 12AWG guarantees a lower voltage drop even when it covers a long distance because of its thickness.
- You can cover longer distances with 12-gauge wiring.
- You can upgrade the circuit to 20 amps without changing the wiring.
- You can operate larger appliances with heavier electrical requirements.
Cons of Using 12 Gauge On 15 Amp Circuit
Many people prefer 14AWG even though 12AWG is thicker because 12-gauge wiring has the following disadvantages:
- 12AWG costs more money than 14AWG because of the superior gauge.
- 12AWG is thicker and heavier and, thus, more challenging to install, especially if you want to pull it through a conduit.
- 12AWG is less flexible.