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

hands working on switches in circuit board

Humans lived without it for tens of thousands of years, but electricity now feels like an absolute necessity to everyday living. And if you've got DIY energy, you might wonder things like, how long can I run 12/2 20 amp circuit and keep everything safe and functioning?

If you don't even understand the question, there's some other stuff you're going to want to know first. Knowing how long you can run 12/2 20 amp circuit means you will have some knowledge of electricity that will serve you when it comes to DIY projects around the house.

What is a 12/2 20 Amp Circuit?

There are lots of things around your house that you can kind of learn something about by examining them or taking them apart, or working on them, such as clogged pipes or sanding down the kitchen cabinets. Your home’s electrical wiring is not one of those things.

In fact, just digging into the wiring to figure out what’s going on is a massively bad idea that you should not do a all.

No one should handle electricity without taking all proper precautions. And if you do not feel confident in your own abilities, don't hesitate to contact a professional.

Call in the calvary before you start playing guessing games or improvising. If there’s one place you don’t want to get creative with your DIY, it is when you’re doing something with electrical wiring.

A 12/2 wire has two 12-gauge wires and a third ground wire. It is quite common in households for 12/2 wire circuits to connect to a 20 amp circuit breaker.

When the electrical energy on the circuit exceeds 20 amps, the breaker will automatically shut off. This is a simple safety measure, and hopefully, you never have it happen to you.

There are some safety features like this that are built in, but for the most part, you will have to be very careful and mindful of your own safety at all times whenever you have exposed wiring, or you’re working with electricity at all.

It is common for 20 amp circuits to be used to power room outlets and overhead lights. You often see 12/2 wiring in homes so it is very likely that if you’re doing some sort of DIY electrical project, you will be working on a 20 amp circuit with 12/2 wiring.

This wire can support both 20 and 15-amp circuits, which means 12/2 wire can be used to power appliances, as well.

What Is a Circuit?

So, what exactly is an electrical circuit? If you want to get scientific about it, a circuit is an unbroken look of material that is conductive, through which an electrical charge can flow.

Now, to put that in more DIY-friendly terms, this is simply a path of wires that electricity flows through. In a typical home electrical circuit, wires run from the circuit breaker panel to the thing that is being powered, such as a light fixture.

The current flows down the wires and back up again in a continuous loop, as long as the circuit is functioning the right way. A circuit is a closed path, meaning it does not connect to other circuits, and it’s doing its own thing.

A single home circuit that supports 20 amps of power can power around 10 outlets, so even one circuit may be responsible for powering several appliances and devices.

You may not always be able to tell which breaker is powering what, so when in doubt, turn off extra breakers or turn them all off.

How Long Can a Circuit Be?

So if a circuit is a loop of electricity and one circuit can power multiple electrical appliances and devices, how long can a 12/2 20 amp circuit be? How can you get this question answered?

Electricity is pretty tricky business, and it is very much a hard science. However, it definitely seems much more like magic than it seems like anything scientific.

Once you know some of the science, it starts to get a little easier to do your own electrical DIY work. However, you don't have to know everything or member a bunch of figures in your head.

As long as you know some simple rules, you can do what needs to be done with your DIY electrical projects.

After all, human beings were around for over 40,000 years before one of them figured out how to capture and use electricity. If someone had figured it out any sooner, they might have been burned at the stake for being a witch.

Hard science or not, there is no super simple answer to the question of how long any circuit can be, or how long a 12/2 circuit can be. However, there are some things to keep in mind and some hard numbers to consider so you can work out how long to run your circuit.

Electricity travels along wires and it will travel along wires from endpoint to endpoint, unless something stops that electrical flow.

That is to say that technically, wires for a circuit can be just as long as you want them to be because the electricity will continue to flow along those wires until it reaches the endpoint...no matter how far away that endpoint is.

However, there is most definitely a point of diminishing returns. The longer the wire is, the weaker the voltage will become as it travels along that wire.

This means that the electrical voltage will get weaker and weaker the longer the wire is. This means the circuit will not be efficiently and effectively delivering power to the things you want to power…which kind of defeats the purpose of having electricity in the first place.

So what you actually need to know is how long your 12/2 20 amp circuit can be before the voltage it is carrying starts to get too weak to do its job. How long can you run this circuit before you lose too much power because of this length?

There are no specific guidelines or hard numbers in the National Electric Code, and there is a lot of information online that gives a few different numbers for how long a 12/2 20 amp circuit may be. It’s easy to get confused and to spend a long time trying to find just one answer.

So it's time to get mathematical. The rule of volt drop is as follows: the drop in voltage on the circuit should not exceed five percent.

If you're using 12-gauge wire on a 20 amp power load, that means you can run the circuit almost as long as 57 feet without experiencing more than a five percent volt drop. Many online sources suggest going no longer than 50 feet for a circuit.

You can always test the voltage on a wire using a multimeter, a tool designed specially to test electrical power, to see if you are losing voltage along the circuit and how much you are losing.

Playing With Fire

In an ancient Greek legend, Prometheus was a Titan and the god of fire. He defied all the other gods by sharing the gift of fire with humans.

This enraged Zeus, the king of the gods, to no end, and Zeus devised a horrific punishment for Prometheus to endure for all time. Electricity is truly a type of godly fire, something that's just on the edge of being too dangerous and too powerful for humans to really control.

After all, it was Zeus himself who was the god of lightning bolts.

The legend serves as a warning to not play with fire, something that has become a wise old adage. It definitely still applies, especially in the case of the awesome power of electricity and all the things it can do.

Before you do anything or touch any wires or start adding any circuits, make sure the power is turned completely off where you are working or better still, to the entire property. Turn off all the breakers to make sure you are working safely.

You cannot possibly be too cautious or too careful when it comes to doing electrical work, so triple-check to make sure the power is off and work very slowly and carefully if you're working with wires for any reason.

When you know you're in over your head or you get too confused to continue, consult with a professional rather than trying to figure it out or rig something up on your own.

Improper electrical wiring is a fire hazard that can be potentially fatal and totally catastrophic. It's better to consult with a professional when needed and spend the money on that than to have a disaster and end up losing far more in the future.

With care and patience, you can wire your own circuits and do many DIY repairs and additions to your home electrical grid. As long as you're safe and careful, just about anything is possible when you've got DIY skills, even when it comes to your electricity.

12/2 20 Amp Circuit FAQ

How far can 12 2 wire carry 20 amps?

As a general rule, a 12/2 wire with a load of 20 amps can be as long as 57 feet before it loses too much voltage to be effective. This is because voltage is lost along the wire the longer the wire is, so length does matter a great deal.

Pay attention to the length of circuits and remember that when you’re working with wires and electricity, every little detail really does matter.

What size wire do I need for a 20 amp circuit?

For a 20 amp circuit, 12-gauge wire is already the ideal choice, though you can also use 10-gauge wire to achieve the same goal. However, 12-gauge is the best size.

Can I mix 12 and 14 gauge wire on a 20 amp circuit?

Most of the time, you do not want to mix and match different sizes of wire on a single circuit. Sometimes things can be done but still should not be done because they're not wise or safe.

Such is the case with mixing different wire sizes. There are ways to do this, yes, but it's unlikely you will pass muster if an inspector takes a look at it because this is not really a safe thing to do and it’s best avoided.

Electrical wire is not expensive. Get the right size to keep things neater and safer.

Should I use 10 or 12-gauge wire for 20 amp circuit?

When you're working with a 20 amp circuit, 12-gauge wire is the right choice. It's more common that 10-gauge wire be used for 30 amps of power.

Knowing which sizes of wire to use for the grid you have is important and it’s good to think about. Wire size, length, these things all matter and must all be considered in you are doing any kind of electrical work.

What can you run off a 20 amp circuit?

A 20 amp circuit has enough power to provide electricity for appliances, outlets, lighting, and devices of all kinds. Many different fixtures and outlets can fit on a single 20 amp circuit, so an entire room and everything in it can be powered by a single circuit.

Further Reading

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7 Common Electrical Problems and How to Solve Them

Everything You Need to Know About Light Fixture Ground Wire

How to Install an Electrical Outlet

How to Install Residential Electrical Wiring

How to Extend a Wall Electrical Outlet

How to Find an Electrical Short

How to Fix an Electrical Ground Wire

How to Hide Electrical Cords

How to Test an Electrical Relay

How to Use Electrical Wire Connectors

Identifying House Electric Wiring Colors

Light Fixture Wire Sizing for Beginners

Moving an Electrical Outlet Step-By-Step

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Wiring a Light Switch in the Middle of a Circuit