125 Amp Wire Size and Breaker Guide

Regarding electrical wiring, the 125 amp wire size and breaker are essential components for a safe and reliable system. Knowing the right wire size and the appropriate amp breaker is critical to ensure your electrical system is up-to-code and can handle all your power needs.

The 125 amp wire size is a 2 AWG copper wire or a 1/0 AWG aluminum wire. The National Electrical Code (NEC) helps set electrical standards to protect against potential overloads, short circuits, and arc faults. Depending on the electrical load, you must increase the wire gauge per 100 feet distance to account for voltage drop.

Use our Residential Electrical Load Calculation to calculate your needed electrical load.

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What Size Wire for 125 Amp Service

With this 125a wire size and breaker guide, you’ll be empowered to ensure your system is up-to-date and can handle all your electrical needs.

So don’t risk it; take the time to think through your electrical project from start to finish, and you’ll be sure to get the power you need without any safety risks or costly mistakes.

  • Always use the 125 amp service wire size specified by the National Electric Code for the amps in your circuit. Be sure never to use a smaller gauge wire than what is recommended.
  • When using a 125-amp circuit breaker, 1-gauge copper or 2/0 aluminum wires must be the conductors.
Wire Size Chart - Wire Gauge Sizing Conductors

By following these guidelines, you’ll have peace of mind that your 125 amp wire size and breaker are up to code and can handle all of your electrical needs. With the proper installation, you won’t have to worry about arcing or short circuits, which can be a major safety hazard.

Please consult a licensed electrician for more detailed information on the 125 amp wire size and breaker. With their expertise, you can rest assured that your electrical system is up-to-code and safe!

Note on Wire Sizes: A #2/0 AWG copper or #4/0 AWG aluminum wire size is also used for 200 amps. The 200 amp wire size you need will increase the longer the distance run to account for voltage drop.

125 Amp Wire Size, Electrician Rewiring Panel

What 125 Amp Wire Size You Need

When determining the 125 amp sub-panel wire size, there are two types of 125 amp wire sizes: 1-gauge copper and 2/0 aluminum. Both have their own advantages, depending on your individual needs.

1-gauge copper is the most common type of wire used in residential and commercial circuits for up to 125 amps. Copper is the best option and provides superior conductivity, meaning it can efficiently handle higher electrical current demands.

2/0 aluminum is another popular wire size for 125 amp sub panel. It costs less money than 1-gauge copper, is lightweight, and has excellent flexibility making it cost-effective for longer distances.

No matter what type of 125 amp wire size you choose, consult a certified electrician for help with the installation and use the size specified by the NEC table for your circuit.

When wiring a 125-amp system, select a 125-amp double pole circuit breaker for a main disconnect. Double pole breakers are rated for 240 volts, providing greater protection against short circuits, arc faults, and overloads.

The wire will have two hot wires, one neutral wire, and one ground wire, regardless if you select 1-gauge copper or 2/0 aluminum.

125 Amp Wire Size for Long Distances

If you’re running a 125 amp circuit for longer distances, such as between two buildings, it’s important to select the correct wire size. For long distances, you’ll need a thicker wire to counteract voltage drop and ensure the circuit works properly at the end of the line. See our 125 amp wire size chart below.

CopperAluminumMaximum Distance
2 AWG1/0 AWG100 feet
1 AWG2/0 AWG200 feet
1/0 AWG3/0 AWG250 feet
2/0 AWG4/0 AWG300 feet
3/0 AWG300 kcmil400 feet
Parameters 230 Volt, Three-phase, 3% voltage drop, 75 degrees C

Aluminum vs Copper Wires

The two main differences between aluminum and copper wires are their resistance to heat and voltage.

Aluminum wires have lower heat resistance and can be used for high-voltage applications. Because of the lower heat resistance, aluminum wires can heat up faster than copper wires, so they must be thicker to carry the same voltage.

On the other hand, copper wires are better at maintaining consistent electrical flow at higher temperatures and offer better conductivity than aluminum wires.

Therefore, a smaller wire can safely carry the maximum current from the main circuit breaker panel to the new sub-panel or appliance. Copper wire material is better for branch circuits to lighting, outlets, and household appliances.

The downside of copper wiring is that it is expensive, especially in larger wires that run long distances. This makes aluminum wire a more cost-effective choice for 125 amp feeder wire, despite the thickness of the wire.

When choosing between aluminum or copper wiring, it’s important to consider the purpose of the wiring and the environment in which it will be used.

Copper wires are typically more expensive than aluminum but are better suited for long runs or high-heat environments.

Aluminum is often used as a cost-effective alternative when copper is not suitable. Ultimately, both types of wiring have advantages and a place in modern electrical work.

Related reading: 80 Amp Wire Size: Breaker & Wiring Gauge Guide


Understanding the size of the wire is important when it comes to electrical wiring projects. When dealing with 125 amp wire sizes, many questions about their size and usage may arise. These are some frequently asked questions (FAQs) related to the wire size of 125 amps and how to use it in any electrical project properly.

What size breaker do I need for a 125 amp sub panel?

You need a 125 Amp 240-volt circuit breaker for a 125 amp breaker box. The main breaker will supply power and serve as a main disconnect for the new subpanel, giving it its own dedicated circuit.

What size wire is good for 120 amps?

The appropriate wire size is 1-gauge copper or 2/0 aluminum wire for 120 amps. For distances longer than 200 feet, you should move up to 1/0 copper or 3/0 aluminum wire to counter voltage drop.

How many amps can a 125 amp panel handle?

A 125 amp panel can handle a maximum of 125 amps. According to the NEC code 80% guideline, the maximum electrical load calculation should not exceed 100 amps.

What size wire for 100 amp service 125 feet away?

To deliver 100 amp electrical service to a 125 amp sub panel 125 feet away at 75 degrees C, you need 1 AWG (American Wire Gauge) copper wire or 2/0 AWG aluminum wire. Some important factors can vary depending on the electrical project. A professional electrician should be consulted for any major wiring jobs.

What size aluminum wire for 125 amp service?

The appropriate aluminum wire size for a 125 amp service depends on the distance between the panel and the load. Choose a wire gauge based on the amperage rating and the wire run length. A recommended gauge for a 125 amp aluminum wire size is 1/0 AWG or 2/0 AWG.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.