What Size Wire For 20 Amp Wire Size

If you want to know what the best 20 amp wire size, then our top pick is the no.12 AWG wire and this is because this wire will be able to safely carry the 20 amps for around 100 feet.

However, if you are looking to wire for more than 100 feet, then you will want to ensure that your wire is running in conduit, so you will want to upgrade your wire to a 10 gauge copper wire.

What Size Wire For 20 Amp Wire Size

Getting a 100 foot 12 AWG wire is not too tricky, and this should be able to handle up to 600 volts.

When you are looking for a wire for jobs like this, there are some particular features you should look out for!

One of the main features needed is flame retardancy, and this should be critical for all of your electrical products, especially if they are going to be outdoors where the chance of running into fire is usually more common.

So make sure to check that the jacket itself has a higher level of flame retardancy.

You also want to look out for moisture resistance as well.

Moisture is well known to cause a lot of issues for electrical equipment and if the water gets into the insulation, it will short your circuit and this will usually damage your device.

This is why the jacket needs to resist moisture. On top of this corrosion resistance is also important.

If chemicals in your wires react they will create a solid material and this can destroy your wire and the whole system, so ensure that the materials your jacket is made from resist corrosion.

However, this is not all that you need to keep in mind when you are putting together a wiring project, and there are extra considerations that you will need to make.

Because of this, we have added some extra information to this guide to ensure that you have all the information needed when wiring 20 amps.

So, if you are doing this project for the first time and need some pointers and extra information, keep reading!

What Is The Ampacity?

If you have heard of amps, but you do not know what ampacity is, then the ampacity of your conductor is defined as how much current you will be able to carry through the conductor safely before it starts to overheat.

The maximum amount of current that is able to flow through your circuit element or circuit conductor should not be going above its ampacity for the sake of safety. 

This concept is usually easier to explain using examples.

So, an example of this is that if you have a 12 AWG copper wire which has an ampacity of 20 amps, then you should not send more than 20 amps through this wire as this will risk it melting and overheating and this will break down the wiring.

If you try and for more than 20 amps to run through this wire, it will overheat and then usually lead to a fire or an electric shock. Because of this, knowing the correct wire size for your job is incredibly important!

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20 Amp Breaker Size

If you are working with a 20 amp breaker, this will also need a wire size of 12 AWG and this is the smallest size you should be using. This is because the AWG gauge of 12 will work for 20 amps.

If you are wanting to make a 20 amp receptacle, then you will need to understand that this will need a 20 amp outlet box as well.

This will need to have an opening that is sufficient enough for the larger cable which will be leading between the breaker panel and the receptacle.

However, there is something important to keep in mind, and that is that you should never mix your wires.

You will not want to use a 14 gauge or a 16 gauge wire on your 20 amp breaker when you are using a No. 12 AWG wire.

If you run out of the wire that you have been using, just go and buy more, and do not try and put any different types of wires to use from earlier projects as this can cause dangerous consequences like those described earlier.

What Is Voltage Drop?

If you have heard of the concept of voltage drop, but you do not know what it actually means, this is the decrease in your voltage level, measured in volts, that will occur when your current passes through resistance.

There are ways you can avoid voltage drop, the main one being you should buy a sufficient size of wire so that your voltage will not drop under 85% of the nominal value. 

There are other methods of avoiding voltage drop besides this. Another way is to use as much 12 AWG copper wire as you can.

This is because this type of wire will not have as much resistance per foot when compared to wires that are a lower gauge than it is.

Max Distributed Load And Max Branch Circuit Load

The total current that is measured in amps for all of the loads that can be given to a single breaker should not exceed 85% of the breaker’s rating.

If this level is then exceeded, you will need to increase the number of fuses or breakers that are used.

On top of this, any one outlet or receptacle, or combination of these will not be able to use over 20% of the branch circuit’s rated capacity.

An example of this is if your main panel has a rating of 100A, then there is no one outlet or receptacle that can be rated for over 20A.

There are other variables that will be involved in the proper wiring of a circuit.

An example of this is the wire ampacity ratifying will assume that it will have the protection of a fuse or of a circuit breaker that has a proper rating.

But if either one of these devices is then undersized, the total current will exceed 85% of the rating and this will likely cause meltdowns or overheating.

On top of this, there are other factors which will reduce the allowed ampacity, these include the exposure to elements like sunlight or moisture, as well as wire length and temperature!

20 Amp Vs 15 Amp

It is worth noting that a 20 amp circuit and a 15 amp circuit will have an almost identical voltage drop, however, your 20 amp circuit is going to carry around 36% more current without having any extra resistance compared to the 15 amp circuit.

However, a partial overload is not going to cause as much damage to a 15 amp circuit than an overload on a 20 amp circuit. This is because your 15 amp fuse will be close to the max rated current.

What Size Wire For 20 Amp Wire Size (1)

Can You Mix 12 And 14 Gauge Wire On A 20 Amp Circuit?

No, you should never do this, this is because if you use a 14 gauge wire, this will be too thin for carrying 20 amps within the home.

This is why it is not recommended to install a 14 gauge wire within the home, the main exception for this is for use in very small appliances like light bulbs.

If you are using these two different types of conductors and installing them next to each other than there is a good chance that your circuit is going to overheat, and then a spark will cause a short.

Avoid mixing wires of different gauges as much as possible!

What Is AWG Or Gauge?

If you have been seeing the term AWG and gauge thrown around, then you might not know what these terms mean.

For a quick answer, AWG is the American Wire Gauge, and this is the system used to standardize wire sizes in America.

Using this system the smaller the number, the larger the overall diameter of the wire will be. You will also find this being called the American standard system as well.

This is used to differentiate from the British standard wire gauge which is also known as the SWG which is used outside of North America.

How Many Outlets On A 20 Amp Circuit?

A 20 amp circuit will usually be able to handle almost any amount of outlets you place along it. This is if you do not try and draw over 80% of these 20 amps.

This is so you will try to be safe when using your outlets to ensure that you are not using more than 16 amps.

The extra leftover 4 amps is there to ensure safety when working with electronics.

You will find that some of your devices will have surges, and this leftover 4 amps is there to ensure that these surges do not cause any issues. 

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How Much Capacity Is Needed?

This is usually worked out by understanding how many watts are being used on each of your circuits.

The bigger the appliance is, the more the wattage will be, and this will need more electricity, and then this will need an increased amp rating as a requirement.

There are other factors that you will need to take into account when you are working out your capacity.

One of the main considerations that needs to be made when working out the capacity that is needed is to work out how often you are using your appliances.

If your appliances are being used quite regularly, then these will need a higher amp wire size (see also: What Size Wire Do You Need For A 40 Amp Breaker?)compared to those which are not used as often.

The regular use of your circuit will cause a greater amount of heat to get generated from the wires.

This heat is known as resistance and this is going to cause voltage drop from your circuit, this is because you are using more power than your wires can carry, so the excess energy is being turned into heat.

So, you could say that if all of these appliances are being used at the same time, then you might need an increased amp wire size (see also: What Size Wire For 15 Amps? Your Complete Guide)since there is going to be a larger amount of power getting drawn from all of the circuits at once.

However, most homeowners tend to only have a couple main appliances in their home that are being permanently used within the house like a wall furnace or an air conditioner.

Everything else is something added later and is only used occasionally, like smaller electronics which do not draw much amperage.

If your circuit is being used for a variety of smaller electronics, or for something that is always turned on, like light fixtures, then this should be wired in an area that has multiple (see also: How To Wire Multiple 12V Or 6V Batteries In Your RV)circuits by itself.

This will not diminish the performance of the other systems that are working in your home and help reduce resistance overall.

What Is A Breaker?

If you are hearing about breakers, but you are unsure what they are actually doing, they are there to interrupt the flow of your electricity, so there are no unwanted overloads.

These breakers will help with preventing fires as well as shocks that would be caused by a circuit getting overloaded.

A common 20 amp breaker will use 2 pins, one will be blue, and the other is usually white, but if it is older could be black. These work great as a safety precaution.

Your circuit breaker uses an RCD which is a residual current device and this is used to detect and electricity leaks, as well as a fuse which is used to help protect you against any overloads.

You want to keep in mind that devices like these are used for safety precautions in case anything goes wrong with your electronics.

So, your RCD on top of the fuse is not something that you want to tamper with, these could be dangerous and if you are unsure what you are doing, you could cause a shock or a fire. 

Your breaker is designed to make it so if you trip it before the wiring gets burned out, your house will be saved from getting burned down, and there will be fewer injuries for those who are at risk of getting shocked.

You will find that most houses and physical businesses will use breakers and the RCDs in their electrical wiring to help maintain this level of safety.

However, breakers were not always included since the risk was not as high as it is now. But since there is more strain currently, then they are needed for safety.

Some common wiring knowledge that can help when it comes to working with a breaker is knowing the right size of wire when working with your 20 amp (see also: What Size Wire For 50 Amp RV)circuit breaker.

You will also want to know how much load you are taking at one time.

A rule to follow is that if you are using multiple appliances and pieces of equipment on your one circuit, then you will need to ensure that everything can get power instead of overloading your outlet which commonly leads to malfunctions and fires.

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Breaker Load

You will want to ensure that your breaker load is not going to be overloaded. In spite of this, if your breaker is overloaded, then it is just going to break.

There is not going to be a fire or an explosion, your breaker will simply need to be replaced, and maybe a bit of repair work as well.

Your circuit will be overloaded by the specifications, however, the reason it is getting overloaded is that something which should not have been possible with a 20 amp system was not able to function.

Your main issue when it comes to overloading your breaker or your switch is that these will not turn off when they are getting overloaded and they will stay on until something eventually gets damaged instead.

Then you are going to need to trace your wires back and shut down different pieces manually until you work out the source.

Your breaker is going to trip when it senses that there is a problem, however, it will not move past the red or the orange range for the trip setting.

Until then, it will stay on and hit the switch contact until it gets damaged.

If you want to look out for clear signs of overload happening, then there are some things you can identify!

    • You will notice the overload if your appliance is plugged into your circuit and your breaker clicks. The light will then stay off because the current is too high for your breaker.

    • When you push the reset or flip the switch on your breaker it will stay off because it senses the overload. 

    • If your outlets or your switches are buzzing or vibrating when you turn the power on and off.

    • A bad smelling odor coming from your outlets or your switches.

    • Any signs of scorching on your plugs or your outlets.

    • Appliances are not getting enough power or do not have enough output.


Hopefully this guide has given you all the information you need when it comes to wiring with a 20 amp system.

Knowing all the correct information when doing this is significantly important because it can help avoid some catastrophic consequences with your electronics.

If you are not fully confident when working with these systems. Then getting professional assistance is recommended.

It is always better to pay a nominal fee for professional help, than clean up after a house fire due to poor wiring technique.

Eddie Meyers
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Eddie Meyers
My name is Eddie, and I am an RV enthusiast! I have enjoyed traveling all my life, and want to give my family the same opportunities to see as much of the world as possible. As I’ve gotten older, I’ve discovered how great RVs can be for vacations with a young family. Here at RV Lifestyle Experts, I want to share my experiences, the tips I’ve picked up along the way. I hope that our guides can encourage you to try the RV lifestyle. I promise you that you won’t regret it!
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