What Size Wire Do I Need For 125 AMP Service?

Though 200 amp service is considered the standard service for houses with electrical equipment, many people still install 125 amp service according to their needs. 125 amps are also ideal for houses with limited electrical appliances. 

For a 125 amp service, you will need a 1 AWG copper wire or 2 AWG aluminum or copper-clad aluminum wire. But, if the distance is more than 50 feet, you should use 2 AWG copper wire. Also, for grounding a 125 amp service, you will need #8 AWG copper wire or #6 AWG Aluminum wire.

However, several factors determine the wire size of the 125 amp service. This guide will give you an idea about the particular service, the wire sizes it requires, and what are the best wire types.

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What is a 125 amp service?

When you check your main panel, you will find that it is written 125 amps. 

It means that your house can handle only 125 amperes of electricity safely. 

The electrical service size will let you know the actual electrical capacity you can avail in your house. 

It will also affect the number and size of the electrical appliances you run at your home.

What size of wire is needed for 125 amp service?

In the old days, 30-50 amps were enough for the houses because they did not use as much electrical equipment as in the present. 

But in today’s world, there has been the introduction of so much electrical equipment to speed up our lives.

Before using them, you must install the correct electrical service to carry your house’s electrical loads. 

So, when you upgrade your service, the wire size will change.

If you use a 125 amp service, the best wire size would be 1 AWG copper or 2 AWG aluminum or copper-clad aluminum. 

Distance affects wiring size.

Though 1 AWG copper wire is enough for 125 amp, you can use a 2 AWG copper wire if the distance between the main panel and subpanel is more than 50 feet.

However, a 1 AWG copper will be enough. 

If the distance is very long, the gauge will need to be higher, and so will the voltage drop. 

A professional can calculate and help you get the right wire gauge size. 

Most professionals recommend 1 AWG copper.

It is enough, and you can get it at an affordable price due to the smaller gauge. 

A wire of 1-2 AWG can be very thick and carry loads of electricity, especially if it is copper.

But, due to the thickness, the wire becomes stiff. 

Both of them will work well with 125 amp.

Depending on the temperature rating, distance, and material, an expert may tell you to decrease or increase.

Besides, the size also depends on the electrical code of your region. 

Different areas have different requirements.

So, first, consult the chart before choosing the wire size. 

It is better to use the right wire size. Otherwise, if you use a smaller wire, the voltage will increase, and the wire won’t be able to hold the current load.

As a result, the wire will heat up and cause a fire hazard. 

Also read: What Kind Of Wire Goes From Meter To Breaker Box?

A wire size table depending on the kind of wire 

The kind of wire also determines the wire size required for 125 amp service.

Kind of wireWire size (copper)Wire size (aluminum or copper-clad aluminum)
Hotwire1 AWG2 AWG
Neutral wire1 AWG2 AWG
Ground wire1 AWG3 AWG
Wire size as per the type of wire

The hot wire carries the current from the main power source to different outlets.

The neutral wire carries from the hot wire and transfers it back to the main power source. 

The wire size of the neutral and live wires must be of the same size since both of them carry currents. 

The ground wire doesn’t have to be the same as neutral or live.

The ground wire helps in safety. 

In situations like electrical accidents and short circuits, the ground wire saves us from shocks. 

The current takes an alternate path and flows through the ground wire instead of your body during short circuits. 

You might have noticed the difference in size due to the wire material, i.e., copper and aluminum or copper-clad aluminum.

A question may arise in your mind: why this difference?

The next point will clear it out.

Why do the wire size for 125 amp service differ depending on the wire types?

The wire size for 125 amp service may differ depending on the material. 

There are three types of wires to use for electrical purposes:

  • Copper
  • Aluminum
  • Copper-clad aluminum

Let’s learn why the size differs.

Copper wiring

Copper wires are the best type of wires for electrical purposes.

The wire may be expensive, but it gives a lot of benefits and stays fine for a very long time. 

Here are some good advantages of copper wires:

  • Copper wires have excellent conductivity. It can carry loads of electricity without getting heated up easily. That is why you can use them for longer distances in smaller gauges. 
  • Copper wires are extremely resistant to heat. The wires don’t get heated up despite carrying high electricity loads. 
  • Copper wires do not contract or expand. They stay tight, and thus, the electricity flow doesn’t get interrupted. 
  • Copper wires are also corrosion-resistant. They have Patina, a tarnish-green color that gets oxidized and changes the color of the wire. It makes the copper resistant to corrosion. 
  • Copper wires are thin and malleable. So, you can mold and use them without fearing breakages. 
  • Since the wires have high conductivity and do not expand, you can use them for longer distances. 

Despite having so many advantages, copper wires are very expensive.

A lot of people won’t be able to afford copper wires. 

So, 1 AWG wire will be enough for 125 amp service if you use copper wires. 

But don’t worry, you can use aluminum for that.

Aluminum wiring

Many people prefer copper over aluminum.

It is because aluminum is:

  • Less conductive
  • Not heat or corrosion-resistant
  • Expands or contracts for which electricity flow is interrupted
  • You will need a wire twice the size of copper to compensate for the above drawbacks. 

But despite so many bad points, people still use aluminum.

Aluminum does have some drawbacks, but they are not a very bad option for electrical purposes. 

It is because:

  • Aluminum is very lightweight compared to copper wires. Due to this, you can easily handle and install them faster than copper wires. 
  • Aluminum is very cheap compared to copper. People who cannot afford copper wires can opt for aluminum. 

But know that the gauge of aluminum must be double the size of copper wires. 

So, if you want to use aluminum wires for 125 amp service, you should choose a 2 AWG wire for hot and neutral wires and 3 AWG for ground wires.

Copper-clad aluminum wiring

Choose copper-clad aluminum if you want a cheaper wire but a better aluminum version with some copper benefits. 

The wire is cheaper than copper but more expensive than aluminum wires. 

These wires have some copper fittings at the ends, which gives some copper benefits.

The wires are not as resistant or good in conductivity as pure copper but a little better than aluminum.

However, the gauge size has to be the same as aluminum. 

If you use copper-clad for 125 amp service, you should take 2 AWG copper-clad.

What size of breaker do you need for a 125 amp service?

A 100A breaker will be good for a 125 amp service.

The breaker should not be very small because it will protect the wires. 

The wires should be large enough to carry enough flow of the current. 

If the wire size is small, it will melt due to the excessive current voltage and, thus, cause a fire hazard. 

The wire can carry as much current as you want, but the breaker will protect it.

It will allow the wires to carry only the specific amount of current they can handle. 

The breaker will trip if excessive current flows, thus saving the wires. 

A small breaker will trip faster as it won’t be able to carry enough current. 

But that doesn’t mean you will take a large breaker.

It would be of the right size. 

For 125 amp service, a 100A breaker is the perfect breaker size. 

How to install a 125 amp service?

If you are inexperienced with electrical wires, consult a professional for work and pay him the right price for the installation. 

Besides, some states do not permit inexperienced people to perform electrical tasks as it can be risky.

Here are the simple steps to install a 125 amp service:

  • First, switch off the main power leading to the meter. 
  • Screw the clamps at the top or bottom, depending on the route of the service wire entrance.
  • Now, run the main to the clamps and secure them with a screwdriver.
  • Locate the brass bar and join the black and red wires to the main lugs. These are the hot wires.
  • In the same way, find the silver bus and join the white wire to the main lug. It is the neutral wire. 
  • Pull a ground wire into the panel and join one end to the ground bus and the other to the ground rod. This wire will be bare. 
  • Take all the circuit wires through the clamps. 
  • Remove the sheathing from the endings of the circuit’s wires. 
  • Also, remove a half inch of insulation from the individual wire ending. 
  • Join the neutral wire with the neutral bus and the bare wire with the ground bus. 
  • Now, connect the black or hot wire with the terminal of the circuit breaker. 
  • Push the circuit breaker inside the hot brass bar. 
  • In the end, run the red and black wire into the two-gang breaker, and your installation is done.

How to understand that I am having a 125 amp service?

It isn’t easy to understand what amp service an individual is having. 

A 100 amp service meter has a glass dome over a square base, while the other services with higher amps have rectangular bases.

A 60 amp will have a meter behind the flat glass window. 

You may know it by checking the breaker at the top.

The main breaker’s amp rating will tell you what amp service you have. 

The main breaker’s amperage rating level is the actual amp service you own in your house. 

You may also have 225 amp service because you have a 125 amp main breaker with a 100 amp sub panel.

Confirm this with your electrician.

How much will a 125 amp service cost?

Getting a 125 amp service is quite costly.

Generally, you can expect it to cost around $1,000.

Sometimes, it can be as high as $2,000.

However, the cost changes depending on various factors, like the labor costs of different states and the time it takes.

Here is a table for your guide:

Time for the installationLabor cost per hourAverage cost
Maximum time 20 hoursMaximum cost $100$2,000
Minimum time 8 hoursThe minimum cost is $40$320
Average time 14 hoursThe average cost is $70$980

Sometimes, the labor cost can be around $800, depending on the hourly rate and job complicacy. 

The price also differs depending on installing a 125 amp service or upgrading from a low service to a 125 amp. 

Here is a table of prices behind upgrading a 125 amp:

Panel cost$250
Average hour14 hours
Labor costs$70
Average upgrade price$1230

Depending on the location, job complicacy, and time required for upgrading, the price may be high or less than $1230. 

Some upgrades can cost only $500.

Final thoughts

The best wire size for 125 amp service is 1 AWG copper wire or 2 AWG aluminum or copper-clad aluminum wire. 

However, you may also use a 2 AWG copper wire, depending on the distance, temperature rating, and material. But since a 1-2 AWG copper wire is very thick and sometimes difficult to handle, professionals prefer 1 AWG copper. 

If you can’t afford copper, you can go for aluminum or copper-clad aluminum. In the case of aluminum, you might have to do some fittings so that it works well. 

The hot and neutral wires should have the size, but the ground can differ. However, if you use copper, 1 AWG copper will be enough. 

A 100A breaker is best for 125 amp service. It will allow the wires to carry a specific amount of current.

If you wish to install a 125 amp wire, follow the steps I have shared without fail. Call an electrician to do the job if you don’t have experience or are confused about the different wires.

Also read: Size Of Ground Wire For 200 Amp Service: Complete Guide With Table


How many wires are required for a 125 amp service?

Only three wires are needed for the main service.

A neutral wire and two hot wires.

What does the NEC code say about the wire size of 125 amp?

NEC recommends customers to use a 1-gauge copper wiring to be the best one for 125 amp.

Data Source: National Electrical Code

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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