What Size Wire for My Breaker Do I Need? (2024)

Whether you have a 30 amp or a 40 amp breaker, wire size is important. Here’s how to determine what size wire you need for your breaker.

Wire is sold based on several factors. The most important part that will be covered here is the gauge, sometimes referred to as AWG (American Wire Gauge).

Gauge is a measurement of a wire, specifically its diameter. AWG is the standardized system of this measurement. Wire gauge is measured from high to low with higher numbers meaning a smaller wire size.

Precise wire sizing is essential for circuit breakers as it helps determine how much electrical current can flow through it and how much resistance it has. The chart below will tell you approximately what wire size is needed for the amount of power that will be running through the line.

Please note that the information within this article is intended only as general guidelines. For any questions, always consult a certified electrician, as well as your local electrical codes.

Wire Size Ampacity Chart

In the chart below, we outline what gauge wire you need for the maximum amperage, or strength, of the electrical current. Note that the gauge can sometimes vary between aluminum and copper wires. Below is the gauge size based on the more commonly used copper wires.

Maximum Amps71015203040557095
Gauge (Wire Size)18161412108642

Here are some more details about some of the more popular amperage sizes. Remember that when you use an appliance, always check the amp requirements first. You can calculate this by dividing Watts by Volts.

10 AMP Wire Size

For a maximum of 10 amps, you’ll need a wire gauge of 16. Common appliances that require around 10 amps include: a toaster, a hair dryer, a vacuum cleaner, a radiator, a washing machine, a dishwasher, and a refrigerator.

30 AMP Wire Size

For a maximum of 30 amps, you’ll need a wire gauge of 10. The most common household item that requires a 30 amp circuit is a central air conditioner.Often, people living in RVs use 30, and sometimes 50, amp systems to run all the appliances in the vehicle.

40 AMP Wire Size

For a maximum of 40 amps, you’ll need a wire gauge of 8. Many electric cooking appliances require 40 amps such as electric cooktops.

50 AMP Wire Size

For a maximum of 50 amps, you’ll need a wire gauge of 6. Fifty amp breakers are most often used to power many different appliances. However, a kitchen oven can alone require 50 amps. Many electric dryers also require a 50 amp breaker.

Reading Cable Labels

You’ll often buy wires in cable, but it’s important to know how to accurately read the product labels in order to purchase the correct product. Here’s a quick look at what to remember:

  • First, you’ll often see the AWG of the wire(s) in the cable. So for a 14 gauge wire, it will read “14.”

  • Next, you may see an additional number. This could read in either of these 2 formats: “14-2” or “14/2.” This number signifies the amount of service wires or conductors in the cable.

  • Then you may see a “G” or “w/G.” Both mean that the cable comes with a ground wire, which does not count towards the total number of wires noted on the label already.

Circuit Breakers

When updating an appliance or air conditioner, it is important to determine the correct current draw.

If your circuit breaker is 20 amps, you cannot install a product that requires 30 amps. It is not as simple as just changing the circuit breaker. The wiring to the appliance also needs to be changed.

Although, when the opposite occurs, the solution is easier. For example, let’s say you were using an appliance that requires 30 amps. If you replace this with a new appliance that only requires 20 amps, you will need to change the circuit breaker and outlet receptacle — but you do not need to change the wire.This is because a wire can safely carry less power than it was rated for without any potential issues. However, a wire cannot carry more power than it was rated for, otherwise it could get hot and create a fire hazard.

What Size Wire for My Breaker Do I Need? (1)Other Aspects to Consider

Wire length:

Under certain circ*mstances a large wire size may be needed even if your amp requirement does not seem to justify it. Go to the next largest wire size if your run is more than 100 feet, inside a conduit, or ganged with other wires where the heat dissipation may be inhibited. As with all electrical work, consult a professional with any questions about special circ*mstances.

Wire material:

If you are using a wire that is not made of copper, brass or silver, you will want to check to see if you need a different size. Aluminum wires are much less common than copper ones, and they also vary from them in requirements: They offer 61% of the conductivity of copper wires but have only 30% of the weight of copper.

What Will Happen With the Wrong Size Wire?

It is incredibly dangerous to use a wire that has a smaller gauge than needed. The wire could overheat and melt. This could lead to breaker or appliance damage and be a fire hazard.

Using a wire that has a larger gauge than needed is not dangerous. It can be an inconvenience, since a larger wire is usually heavier and stiffer, but it won’t lead to any potential hazards.

Finding the right wire size is an essential step to any electrical project or circuit breaker set-up. It’s especially important to remember that it’s about more than just the number — remember to consider all the possible factors when it comes to wire gauge. The information in this article is only a guide — we highly recommend that you consult with your electrician, and check your local and national electrical codes, before purchasing and installing wires.

What Size Wire for My Breaker Do I Need? (2024)

FAQs

What Size Wire for My Breaker Do I Need? ›

Multiply the amperage by 0.8. This is because a circuit breaker should never exceed 80% of its max amperage. Not doing this could leave room for calculation errors, or even worse – electrical fires! Calculate the amperage draw of ALL the devices you wish to plug into the circuit.

How do I know what size wire and breaker I need? ›

You can calculate this by dividing Watts by Volts.
  1. 10 AMP Wire Size. For a maximum of 10 amps, you'll need a wire gauge of 16. ...
  2. 30 AMP Wire Size. For a maximum of 30 amps, you'll need a wire gauge of 10. ...
  3. 40 AMP Wire Size. For a maximum of 40 amps, you'll need a wire gauge of 8. ...
  4. 50 AMP Wire Size. ...
  5. Circuit Breakers.

How do I know what size breaker I need? ›

Multiply the amperage by 0.8. This is because a circuit breaker should never exceed 80% of its max amperage. Not doing this could leave room for calculation errors, or even worse – electrical fires! Calculate the amperage draw of ALL the devices you wish to plug into the circuit.

What size wire do I need for a 30 amp 220 breaker? ›

In most cases, 10-gauge wire is the best choice for a 30 amp circuit breaker. However, depending on your load requirements, you may need to use a heavier gauge of wire, such as 8-gauge.

What size wire do you need for a 50 amp breaker? ›

Based on allowable ampacities of the aluminum and copper wires, you should use 6 AWG copper wires and 4 AWG aluminum wires in the 50 Amp circuit breaker. These are the recommendations for cables that run for 100 feet or less, the most common distance for cables powering the 50 Amp circuit breaker.

How far will 6 gauge wire carry 50 amps? ›

According to the National Electric Code, a 6-gauge wire can safely carry 50 amps for up to 100 feet. Beyond that distance, the wire may experience voltage drop and potential overheating, which can be hazardous.

What wire size do I need? ›

Electrical Wire 101: The Importance of Choosing the Right Size
Wire GaugeAMPSAppliances
14 Gauge15 AmpsLighting circuits, light fixtures
12 Gauge20 AmpsOutdoor receptacles, kitchen, bathroom
10 Gauge30 AmpsElectric clothes dryer, air conditioning
8 Gauge40 AmpsFeeder and large appliance wire
4 more rows
Jan 12, 2023

How to determine wire size for an amp? ›

As with the power wire, the longer the run and the more current you're pushing through it, the larger size you should use. For example, if your amp is in the trunk and you're sending 100 watts to your front speakers, 14-gauge speaker wire is a good call. But if the amp is only 50 watts, 16-gauge would be fine.

What size of wire do I need for a 60 amp breaker? ›

For a 60-amp circuit, a 4 AWG battery cable is often recommended. This size ensures the cable can safely handle the current without overheating, thus maximizing system efficiency and safety.

What size wire do I need for a 30 amp breaker? ›

So, what size wire for 30-amp breakers? Assuming you're using copper wires, the recommended 30-amp breaker wire size is an AWG of 10. Please note that a 10-gauge wire is the minimum size—but you can use a thicker gauge wire. This is because a wire can safely conduct less power than it was rated for.

Can I use 10/2 wire for a 30 amp breaker? ›

30 amp breakers must have 10/2 or larger wire is right. In your case you should remove the 30 amp breakers and replace with 20 amp breakers. 12/2 is usually the largest wire you want for most home electrical devices(lights, outlets).

How far can you run 10/2 wire on a 30 amp breaker? ›

What's the maximum distance 10/2 wire can be run for a 30-amp circuit? The max distance we can run 10/2 wire without worrying about voltage drop is generally about 150 feet. Beyond that, you might need thicker wire to keep things efficient and safe.

How far can you run 12 gauge wire on a 20 amp circuit? ›

NEC (in the US) recommends no more than 3% voltage drop. For 12-gauge wire, operated at 20 amps, that would 51 feet. At that round-trip distance, there'd be 2.95% voltage drop. 116.4 vac instead of 120 vac.

Will #8 wire carry 50 amps? ›

8AWG THHN wire can handle 55amps, and 8AWG THWN can handle 50amps, a 50 amp breaker is appropriate for those types of wire. However, you may not use 8AWG NM-B(aka Romex) on a 50amp breaker, it can only handle 40amps. According to the Canadian Electrical Code (where I live) 8 AWG is only good for 50 amps.

Will 10 gauge wire carry 50 amps? ›

A 10-gauge copper wire is commonly rated for around 30-35 amps in residential applications according to the National Electrical Code (NEC). For higher amperage requirements like 50 amps, a larger wire size, typically 6-gauge.

How many amps is a 6 gauge wire? ›

Note that the ampacity of the wire can be reduced if the cable is bundled with other cables or is placed in high ambient temperatures. However, the regular ampacity of a 6 AWG copper wire that you are looking at in most installations is 55 to 65 amps. It can carry 55 amps, 60 amps, and 65 amps.

How do I know if I need a 15 or 20 amp breaker? ›

The type of outlet you install depends on the room and circuit breaker. If you're wiring a residential space to plug in lights and other everyday electronics that don't exceed 15 amps, install a 15A outlet. If you're working on a kitchen or laundry room and have a 20A circuit breaker, put in a 20A outlet.

Can I use a 60 amp breaker with 6 gauge wire? ›

PV wire is often double-insulated and rated for direct burial, providing the robustness needed for external circuits. When used in a 60-amp circuit, PV wire should generally be 6 AWG in size, providing ample capacity to handle the load.

How far can you run 12-gauge wire on a 20 amp circuit? ›

NEC (in the US) recommends no more than 3% voltage drop. For 12-gauge wire, operated at 20 amps, that would 51 feet. At that round-trip distance, there'd be 2.95% voltage drop. 116.4 vac instead of 120 vac.

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