How Long Can I Run 12/2 20 Amp Circuit?

electrician working with red wires

In recent years, more people have found interest in connecting their outside garden buildings to electricity. The demand for power comes with an increasing need for comfort in an outdoor space.

However, many DIYers find the entire process quite challenging. Among the top questions asked is what are the right cables to use for outbound connection and whether the cable should be underground or above the surface.

In this article, we'll focus on addressing the question, "Is using a 12/2 wire for a 20-amp outbound connection right or possible?" Well, as you can see, the DIYer needs to know whether it is possible and if it is also right. To answer this question, we will have to consider a few factors.

These may include the amount of energy needed by the small house. The other factors to consider are the number of appliances that will be running at the same time and the distance you will need to run the cables from the main power supply.

Understand the Basic American Wire Gauge

To fully answer this question, we first have to understand the standard wire gauge ratings used in America. These gauge ratings determine the capacity of the wire and the suitability of that wire for specific locations.

The basic wire ratings used commonly for domestic wiring include 10/2, 12/2, and 14/3. The numbers indicate the size of the wire and, consequently, the power that it can convey at the same time.

The conductor used should be able to handle the indicated capacity. Further, the insulation should be able to offer sufficient protection based on the amp capacity of the cable.

For instance, a 10/2 wire is normally rated 30 amps. This means that connecting a #10 wire to a 30 amp circuit will work just fine. This wire can be used on all circuits with an amperage below 30 without the risk of overheating.

On the other hand, we have the 12/2 wire, which is generally rated at 20 amps. In other words, the wire can be used on 20-amp circuits comfortably. It will also work on lower-rated circuits.

As you can see from the example above, the capacity of the cable favors a lower cable rating. A #10 cable is more highly rated in amperage than a #12 cable, and so is a #12 cable compared to a #14 cable.

In the case of our question, the DIYer wants to run power from a 20 amps outlet. Well, the rating question then becomes should the #12 or #10 cable be used?"

hands working with electrical wire

Calculating the Right Amperage for Circuit Cables

One of the mistakes that most people make is to assume that, as long as an outlet is rated 20amps, the wire will also be carrying 20 amps. On the contrary, an outlet could be rated 20 amps, but only 5 or 10 amps will be used at every point in time.

As such, it is always important to start by factoring in the appliances to be used at the other end. In this regard, make sure you clearly define the maximum number of appliances that are likely to be running at the same time.

In the case where there are no heavy appliances to be used, the power to be used on the other end is way lower than the outlet amperage. In the case of our question, a 20 amps outlet should work perfectly with a 12/2 wire.

This is because the wire size fits perfectly with the ports provided at the outlet. Further, the amperage for the wire matches squarely with the outlet.

With that said, there are situations where you may want to use the #14 wire for the same. Although not recommended, the #14 wire could be used as long as the appliances to be used will not require the full amperage.

On average, #14 wires have an ampacity of 15amps. This makes the cable ideal for a setup where consumption at every single moment does not exceed 15 amps.

wire unified with connectors

Bottom Line

When trying to wire power outwards, you must first consider the power needs of your outer house. You also should pick a wire that answers your amperage needs, and everything will run fine.

You must also consider how deep your wire should be buried by looking at the type of insulation available on each cable type. In regards to the distance, there is no need to worry as long as the outer source is within the vicinity of the power source.