By Erik Watkins

What Size Wire For A 125 Amp Service?

Last updated: Mar 11, 2023
Size Wire For A 125 Amp Service

To know what size wire for a 125 amp service, You’ll need to think about the required entire load electrical current, distance, electrical panel capacity, ambient temperature tolerances, and so on.

If you are a homeowner, you will need 100 A and a #1 copper or #1/10 aluminum wire to supply a 125 amp sub panel located within 100 feet. We will explain more and provide some helpful hints below.

What Does 125 Amp Service Mean?

If you see 125 amps in the service panel, your electrical service can handle 125 amps. For instance, the overall maximum current capacity of the bus bars is 125 A.

The overall current carrying capacity available to you is considered as the size of the electrical service provided to your home. The maximum allowed flow of electricity through your home is shown. The amperage of a home’s electricity supply is not chosen at random. Because it may impact the number of electrical equipment, you can operate at home.

The service panel supplies electricity to your house. Most residences have two overhead or subsurface 120V service cables that will end at the electrical service panel.

The panel delivers wired power to branch circuits. The panel contains two 120V bus bars, and the number of bus bars linked to each branch circuit determines its input voltage.

One bus bar supplies 120 volts to the branch circuit, while two bus bars may provide 240 volts to a branch circuit. The display shows the electricity service capacity.

Why Do We Need 125-Amp Service?

Careful consideration must be given when choosing an electricity provider. For example, the number of appliances you can power with a given electrical outlet is directly proportional to the size of the outlet.

100-amp panels are recommended for modern 1,200-foot homes. The NEC demands this minimum amp capacity. It powers all essentials—240V appliances.

One hundred amps are too low. This capacity is more common in older, smaller homes without high-end kitchen and laundry facilities or strong air conditioners.

Medium-capacity 100A services. Upgrade to 125, 150, or 200 amps. 150A panels are substantial electrical services. Therefore, your electrical circuit can handle all your heating and cooling systems. 125-200A is standard. Increase capacity to 400 amps.

The typical dwelling needs less electricity. 400A services are only seen in houses with power-hungry hot tubs. Your local contractor may ask you to assess your electrical needs before upgrading the panel to 400A. Additionally, 200A panels are sufficient for home appliances and electronics.

What Size Wire For A 125 Amp Service?

125 Amp Service

100A requires 1 AWG service wire. 125A? Should the electrical wire size be increased to 125 amps? Nope. 1 AWG copper wire can carry 125 amps.

The copper wire size is determined by ambient temperature, distance, and material. 1 AWG and 2/0 AWG wires are pretty thick and can carry a lot of power. Their size, on the other hand, causes them to be very stiff.

This makes the use of PVC conduit challenging. These cables might be routed via pipes. However, it is time-consuming, and individual wires are preferable. Additionally,  service wire jackets that are too stiff make installation difficult.

Why Temperature And Electrical Load Specifications Are Crucial?

A 2/0 aluminum wire will be needed rather than the 125 amp cable if the maximum load is increased to 125A. In this scenario, for safety’s sake, you should upgrade your circuit breakers to 175A.

We have the amperage rating of the circuit breaker, but how can we use that information to get the total load? In most cases, we use a 0.8 multiplier for calculating loads. For example, a circuit breaker rated for 120A can handle up to 175A but only 140A after multiplying by 0.8. Use a 175A and a 2/0 125 amp cable.

What do we call the average temperature outside? Use this table as a quick reference guide. Whether or not a wire needs a temperature rating or a specific capacity depends on the wire itself.

As this 125A wire size chart from various software and electric code requirements (like Canada’s National Electric Code) demonstrates, these amp wire size limits are still proportionate to the breaker and are given globally.

The video is the best way to determine which size to use based on your essential appliances and how much power they usually use. Check it out to learn more!

Why Is Distance Important?

To figure out what gauge wire you need for a 125-amp breaker, you’ll need to know how far you’ll be running the wire. For example, if your task is to run the wire from your main circuit breaker to your garage, you should figure out how far that is. It is just as crucial as amps when figuring up the permissible voltage drop index.

It’s common practice to use this calculator when gauging needs. Instead, a reasonable load should be used on a regular basis. Instead of tripping the breaker, the sensible pack calculates how much power each device needs.

If the distance is less than the voltage, voltage drop calculations are seldom necessary (e.g., 360 V can cover 360 feet). However, voltage drop estimates are only required if it does or is as close as possible.

The Electrical Engineering Portal recommends using ampere-feet to determine the maximum voltage drop. Usually, you multiply the capacity or circuit current (in amps) by the length of the circuit to get this number. For instance, multiply by 100 and divide by the VD value determined in the tables.

If There Is Not Enough Space Anymore In Your Panel? What Should You Do?

Lack of available space is another issue many individuals discover after the fact and must address. For example, there needs to be more room in your electrical panel for the correct-sized electrical cable. Most electricians will tell homeowners that the more space they can dedicate to the control panel or amp sub-panel, the better.

Customers should buy an amp sub panel in lieu of the main panel in cases like this one. You could, for instance, use a 100A breaker from the motherboard to power a 125A panel. It is important to match the capacity of the new sub-panel to that of the main panel.


How Much Does A 125-Amp Service Cost?

You have to pay $1,100 for it. In certain situations, though, the estimate was as high as $2,700. The cost will vary based on several things. Some states, for example, have more extraordinary labor expenses than others. It’s just as crucial to know where you get your components from. Some shops charge more than others.

Before providing a quote, your contractor will consider the task’s difficulty: the more complex the installation, the more expensive the job.

Are 125 Amps Enough For A House?

Maybe for a modest residence. Suppose it is equipped with natural gas.

Some projects are all electric or entirely natural gas. Therefore, they have approximately the same footprint and roughly the same equipment.

Use NEC Article 220 to calculate your loads on a 120/240V panel to see whether the home can manage them. If the results are less than 125A, you’re OK. If not, you’ll need to scale down the service.

What Is Breaker Size For 125 Amp Service?

On a 125-amp panel, there is a 100-amp breaker. Breakers protect circuit wires, and most people understand that electrical service entry wire size is essential.

Amplifier conductors must be large enough to carry power without overheating. Fires are started when little circuit wires melt. Wires cannot control electrical flow.

An amp-rated conductor may handle any quantity of electricity. Only the breaker offers protection. It restricts the passage of electricity across electric wires. Over that limit, the breaker will trip, cutting power and saving the cables.

Miniature breakers trip before your electrical devices acquires power. A larger breaker will be needed to protect the lines quickly enough. As a result, breaker size is crucial. It must be the appropriate size.

In a nutshell, 125-A panels may employ 100-A breakers. Furthermore, 125-amp panels do not need 125 amps. Reduce the amps. The difference between a 100-amp breaker and a 125-amp panel is small enough to cause damage to your equipment.


All in all, A 125A service may be operated using the 1AWG amp wire. Furthermore, always be aware of the facts ahead of time. If you’re looking to upgrade to a 125-amp service, you’ll need to consider the electrical load, temperature rating, and, if applicable, the distance required for the full wiring.

Automotive Mechanic at PowerAll

With 7 years experience in management positions leading automotive mechanics at PowerAll, Erik Watkins wishes to share useful knowledge and information about automotive mechanical equipment.


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