100 Amp Wire Size (The Ultimate Guide)


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Do you know what happens when you use the wrong wire size for a 100 amp sub panel that’s located 200 feet away?

It’s not pretty.

Electrical systems can be dangerous, and using incorrect wire sizes can lead to overheating, fire hazards, and other very serious issues.

That’s why choosing the correct wire size for your sub-panel is critical for ensuring safety and functionality.

For instance – what size wire should you use for a 100 amp sub-panel that’s 200 feet away?

The recommended wire size for a 100 amp sub-panel that’s 200 feet away is typically a 1-gauge copper wire.

What about a sub-panel that’s 100 feet away?

For a sub-panel that’s 100 feet away, generally speaking, a 3-gauge copper wire or a 1/0 aluminum wire is typically used for this application.

But how do you know?

What factors do you need to take into account?

In this article, we’ll explore the importance of wire sizing for 100 amp sub panels. But before we dive into that, let’s first understand why wire sizing is so essential.

By the way – before we get too far along here, if you want to connect with other homeowners, DIYers, and builders and get more great ideas for your home to make your space the best join my free private Facebook group, Remodel Reality here.

Getting Wired: The Importance of Proper 100 Amp Wire Sizing for Your Electrical Needs

When we talk about 100 amp wire size, we’re referring to the amount of electrical current that the wire can handle without overheating. The American Wire Gauge (AWG) standard is used to measure the size of wires, and in the case of 100 amps, we’re usually looking at wires with a gauge of 2/0 or larger. This size wire is commonly used for main service panels, which are responsible for providing power to your entire home.

Using the correct wire size is critical to ensuring the safety and functionality of your electrical system. If the wire is too small for the amount of current it needs to carry, it can overheat and potentially start an electrical fire. On the other hand, if the wire is too large, it can be more expensive and difficult to work with, and it may not fit in the space provided. Choosing the right wire size is essential to making sure your electrical system runs smoothly and safely.

There are many related topics and questions when it comes to 100 amp wire size, including what size wire to use for different types of services and circuits, how to calculate the correct wire size, and what type of wire to use. Some common questions include:

  • What size wire do I need for a 100 amp subpanel?
  • How many amps can I put in a 100 amp box?
  • What gauge wire is good for amps?
  • Can I use 200 amp wire for 100 amp service?
  • What size wire do I need for 300 amps?

Answering these questions requires an understanding of the different factors that affect wire size, such as the length of the wire, the material it’s made of, and the load requirements of the circuit. By taking the time to research and understand these factors, you can ensure that you’re choosing the right wire size for your specific project.

Understanding Electrical Circuits

As a homeowner or a DIYer, it’s important to have a basic understanding of electrical circuits if you’re even thinking about touching anything electrical.

What’s an electrical circuit?

An electrical circuit is a system designed to provide electrical energy to perform a specific task, such as powering a light bulb or a household appliance. It consists of a power source, conductive wiring, and various components that work together to transfer and control electrical energy.

Components of an electrical circuit

The four primary components of an electrical circuit are the power source, conductors, loads, and control devices. The power source provides the electrical energy, the conductors carry it, the loads consume it, and the control devices regulate and protect the circuit.

Types of electrical circuits

There are several types of electrical circuits that you may encounter, including series circuits, parallel circuits, and combination circuits. Series circuits have a single path for current flow, while parallel circuits have multiple paths. Combination circuits are a mix of both series and parallel circuits.

Wire Size and Ampacity

Wire size is an essential consideration when it comes to electrical installations. The correct wire size ensures that the electrical system runs efficiently and safely. It is critical to understand the concept of ampacity to determine the correct wire size.

Definition of Ampacity

According to the National Fire Protection Association’s National Electric Code (more on that in just a minute), ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating[1]. Current is measured in amperes or “amps.” You must use the correct size wire for the current (load) requirement of the circuit to prevent the wire from overheating.

Factors that Determine Ampacity

The number and type of electrical devices connected to a circuit determine the ampacity requirement of the conductor. Usually, a general-purpose house circuit is designed for 20 amps. Lighting circuits may be designed for only 15 amps. To calculate the load requirement for a circuit, first, add up the wattage of all the electrical devices that will be on the circuit. Then, divide the total wattage by the voltage of the system, typically 120 or 240, and that will give you the required current or amps.

National Electrical Code (NEC) Standards

The National Electrical Code (NEC) is a standardized guide for the safe installation of electrical wiring and equipment in the United States. The NEC provides guidelines for the correct wire size to use in electrical installations to ensure that the electrical system operates safely and efficiently. It specifies the maximum allowable ampacity for different wire sizes based on their application.

American Wire Gauge (AWG)

The American Wire Gauge (AWG) system is a standardized wire gauge system used predominantly in the United States. It is used to determine the diameter of electrically conducting wire. As the wire gauge number increases, the wire diameter decreases. This means that a smaller wire gauge number has a larger diameter, and a larger wire gauge number has a smaller diameter.

Table of Wire Gauge Sizes and Amp Ratings

The table below shows the recommended wire sizes and corresponding amp ratings for copper and aluminum wires at different temperatures. It is essential to consult a qualified electrician or professional engineer to determine the appropriate values for your specific application.

Copper vs. Aluminum Wiring

Copper and aluminum are the two most common materials used for electrical wiring. Copper has a higher conductivity than aluminum and is a better choice for low-amp applications. Aluminum has a lower conductivity but is lighter and more affordable than copper, making it ideal for high-amp applications.

Temperature Ratings

Wire insulation has a temperature rating that specifies the maximum temperature it can safely handle without melting or deteriorating. It’s crucial to select a wire with insulation that has a temperature rating suitable for the application’s environment.

Voltage Drop and Voltage Requirements

Voltage drop refers to the reduction in voltage that occurs as electricity travels through a wire. Voltage drop can result in electrical devices not working correctly, overheating, or even starting fires. It’s important to select a wire size that can handle the voltage requirement of the circuit without excessive voltage drop.

Calculation of Amp Wire Size

Calculating the correct amp wire size requires taking into consideration several factors, including the length of the wire, the electrical load, the voltage, and the ambient temperature. You can use online calculators or consult with a licensed electrician to determine the correct amp wire size for your application.

Correct Wire Size for Different Amp Services

The correct wire size for different amp services depends on the specific application and the National Electrical Code’s guidelines. For example, a 100-amp service requires a minimum wire size of #2 copper or #1/0 aluminum, while a 200-amp service requires a minimum wire size of #2/0 copper or #4/0 aluminum.

Wire Size for Different Cable Lengths

The length of the wire affects its ampacity rating, and longer cable lengths require larger wire sizes to maintain a safe current level. It’s essential to select the correct wire size based on the cable length to ensure that the wire can handle the electrical load without overheating or causing electrical hazards.

Wire gauge sizing chart

To calculate how much current a circuit needs, start by adding up the wattage of all devices connected to it. Then divide this total wattage by either 120 or 240 (depending on your system voltage) and that will give you the amount of current, or amps, needed for that circuit. For example, if you had a lighting circuit with five lamps at 60 watts each – that’s 300 watts in total – divided by 120 volts would equal 2.5 amps (A).

Check out the table below for recommended wires sizes and corresponding amp ratings according to NEC Code AWG standards. Note: these values don’t include any temperature correction or other adjustments that might be necessary based on local building codes and regulations. When in doubt, get advice from a qualified electrician or professional engineer who can make sure you’re using safe wiring practices for your specific application.

Wire Gauge Size Copper 60°C (140°F) Copper 75°C (167°F) Copper 90°C (194°F) Aluminum 75°C (167°F) Aluminum 90°C (194°F)
14 15 20 25
12 20 25 30 20 25
10 30 35 40 30 35
8 40 50 55 40 45
6 55 65 75 50 55
4 70 85 95 65 75
3 85 100 115 75 85
2 95 115 130 90 100
1 130 145 100 115
1/0 150 170 120 135
2/0 175 195 135 150
3/0 200 225 155 175
4/0 230 260 180 205
250 255 290 205 230
300 285 320 230 260
350 310 350 250 280
500 380 430 310 350
600 420 475 340 385
750 475 535 385 435
1000 545 615 445 500

Installing electrical wire can be dangerous if done incorrectly, so always take care when completing any wiring project – consult local building codes and safety guidelines!

100 Amp Service and Sub-Panels

A 100 amp service and sub-panel is a common electrical system for most homes. This sub-panel is responsible for the distribution of electricity throughout your home, making it an essential part of your electrical system.

What is a 100 amp service?

When it comes to upgrading or installing a new electrical service in your home, one of the most common options is a 100 amp service. This service provides enough power for a typical home with moderate electrical needs. Essentially, a 100 amp service means that the main breaker panel is rated to handle up to 100 amps of electrical current flowing through it at any given time. This means that the panel can supply up to 100 amps of power to all of the circuits in your home.

Sub-panels and their uses

In some cases, you may find that your electrical needs require more circuits than your main breaker panel can handle. This is where sub-panels come into play. A sub-panel is a smaller breaker panel that is connected to the main panel and can handle additional circuits. It’s essentially a way to expand the number of circuits in your home without having to upgrade the entire electrical service. Sub-panels can be installed in various areas throughout the home, such as in a garage, workshop, or basement.

Wire size for a 100 amp sub-panel

When it comes to wiring a 100 amp sub-panel, it’s important to use the correct wire size. The wire size needed for a 100 amp sub-panel depends on the distance between the main panel and the sub-panel, as well as the anticipated load that the sub-panel will be handling. Generally, for distances up to 100 feet, a #3 AWG copper wire or a #1/0 AWG aluminum wire is suitable for a 100 amp sub-panel. For longer distances, larger wire sizes may be required.

How many amps can a 100 amp panel handle?

While a 100 amp panel is rated to handle up to 100 amps of electrical current, the actual number of amps it can handle will depend on the total load of all the circuits connected to it. The total load of all the circuits in your home should not exceed the panel’s amp rating. Additionally, it’s important to remember that some appliances and devices require more power than others. It’s always a good idea to consult with a licensed electrician to determine if a 100 amp panel is sufficient for your home’s needs.

Upgrading from a 100 amp service

If you find that your home’s electrical needs exceed the capacity of a 100 amp service, it may be time to consider upgrading to a higher amp service. This may involve upgrading the main panel, replacing the service cable, and installing a new meter socket. Upgrading to a higher amp service can provide more power for your home’s electrical needs, but it’s important to keep in mind that it can be a costly and time-consuming process. It’s always a good idea to consult with a licensed electrician to determine the best course of action for your home.

Copper vs Aluminum Wiring

When it comes to choosing the right type of electrical wiring for your home, copper and aluminum are the two most commonly used materials. Each material has its own advantages and disadvantages, so it’s important to weigh the pros and cons before making a decision.

Advantages and Disadvantages of Copper Wiring

Copper wiring has been the standard forever because of its high conductivity, durability, and resistance to corrosion. It’s also relatively easy to work with and has a lower risk of loosening connections over time. However, copper wiring is more expensive than aluminum wiring and can be more difficult to install in certain situations.

Advantages and Disadvantages of Aluminum Wiring

Aluminum wiring is less expensive than copper wiring and can handle high loads well. However, it has a higher risk of overheating and loosening connections over time, which can be dangerous. Aluminum wiring can also be more difficult to work with due to its tendency to oxidize and form a layer of corrosion on its surface.

Copper-Clad Aluminum Wiring

Copper-clad aluminum (CCA) wiring is a newer option that combines the benefits of both copper and aluminum wiring. It consists of an aluminum core with a thin layer of copper coating, providing high conductivity while reducing the risk of overheating and loosening connections. However, CCA wiring is not as widely available as traditional copper or aluminum wiring, and some electricians may not be familiar with its installation and maintenance.

When deciding between copper and aluminum wiring, it’s important to consider the specific needs and requirements of your electrical system, as well as the expertise of your electrician. By understanding the advantages and disadvantages of each type of wiring, you can make an informed decision that will ensure the safety and efficiency of your electrical system.

Copper Wiring Aluminum Wiring Copper-Clad Wiring
Conductor Type Pure Copper Aluminum Copper Clad on Steel
Advantages High conductivity, corrosion resistance, long lifespan Light weight, cost-effective Combines advantages of both copper and steel, easy to work with
Disadvantages Expensive, heavy, can corrode over time Less conductive, more prone to oxidation Not as conductive as pure copper
Choosing Gauge Based on amperage and distance of the circuit Based on amperage and distance of the circuit, but larger gauge necessary due to lower conductivity Same as copper wiring, but use the gauge appropriate for the steel core

When choosing between copper and aluminum wiring, it’s important to consider the distance of the circuit and the amperage being carried. While copper wiring is generally more conductive and long-lasting, it can also be more expensive and heavy. Aluminum wiring is a cost-effective alternative but may require a larger gauge due to its lower conductivity. Copper-clad wiring offers a compromise, with the advantages of both copper and steel, but may not be as conductive as pure copper. It’s important to consult a licensed electrician when choosing the correct wire size for your specific application to ensure safe and efficient electrical work.

Choosing The Correct Wire Size

Now that you have a good understanding of the different wire sizes, it’s important to know how to choose the correct wire size for your electrical project. There are a variety of factors to consider, such as the length of the wire run, the expected load, and the type of wire you’ll be using.

Factors to consider when choosing wire size

  1. Current or Load Requirements The current or load requirement of your circuit is the most important factor to consider when selecting the appropriate wire size. You need to ensure that the wire can handle the maximum amount of current that will be drawn by all of the devices on that circuit.
  2. Distance The distance between the power source and the device being powered is also an important factor when selecting the appropriate wire size. Longer distances require larger wire sizes to prevent voltage drop, which can result in underpowered devices and even damage to the equipment.
  3. Temperature The temperature of the environment where the wire will be installed is another factor to consider when selecting the appropriate wire size. Higher temperatures can reduce the wire’s current-carrying capacity, so you may need to choose a larger wire size to compensate.

Wire size tool

Using a wire size tool or calculator can help you determine the appropriate wire size for your project based on the factors mentioned above. There are many online resources available that can assist with this process.

Consultation with a licensed electrician

If you are unsure about the appropriate wire size for your project or need more information, it is always best to consult with a licensed electrician. They can help ensure that you select the correct wire size and meet all local codes and requirements.

Local codes and requirements

It is essential to understand your local codes and requirements when selecting the appropriate wire size for your project. Different areas may have different rules and regulations that dictate the minimum wire size for certain types of circuits or applications.

Maximizing Efficiency and Performance: Wire Types and Voltage Drop Considerations

There are several factors to consider, such as conductor size, type of conductor, and code requirements. One of the most important considerations is the ampacity, or the maximum current a conductor can carry continuously without exceeding its temperature rating.

When it comes to wire types, there are several options to choose from. Three-wire cable and AWG cable are common choices for electrical projects. Three-wire cable contains a hot wire, a neutral wire, and a ground wire, and is typically used for single-phase circuits. AWG cable, on the other hand, refers to a range of wire sizes and is often used in branch circuits.

If your project involves long runs or thicker wires, it is important to minimize voltage drop. This is the reduction in voltage that occurs when electricity travels over a long distance. To minimize voltage drop, it is important to choose the correct gauge wire and to use a voltage drop calculator to determine the maximum length of wire you can use. In addition, using a thicker wire can help reduce voltage drop.

These concepts apply to both residential and multifamily dwellings in North America. For example, silver wire is a popular choice for underground service and can be used to achieve similar results as thicker wires. It is important to adhere to code requirements and consult with a certified electrician to ensure the correct wire size and type is used for your project.

Whether you are working on a main service panel, an amp sub-panel, or a feeder cable, selecting the right wire size and type is critical to ensure safety and prevent electrical fires.

Related Questions

Q: What size cable do I need for 100 amp?

A: The size of the cable for a 100 amp service depends on the distance from the main panel to the sub-panel, the conductor material, and the type of insulation. For copper wiring, typically 2/0 or 3/0 AWG cables are used for longer distances, while 4/0 or 250 kcmil AWG cables are recommended for aluminum wiring.

Q: What size wire do I need for 3 phase 100 amp service?

A: The size of wire for a 3-phase 100 amp service is determined by the distance between the main panel and the sub-panel, the type of insulation, and the conductor material. Copper wiring is recommended to be between 1/0 AWG to 3/0 AWG, while aluminum wiring is recommended to be between 2/0 AWG to 4/0 AWG.

Q: Can I use #4 copper wire for 100 amp service?

A: No, #4 copper wire is not recommended for a 100 amp service. It is rated for 65 amps and may cause overheating and damage to the wire.

Q: How many amps can you put in a 100 amp box?

A: A 100 amp box can safely handle up to 100 amps of electricity flowing through it. However, it’s important to consider the individual circuits and the total load they place on the panel.

Q: How many volts is a 100 amp panel?

A: A 100 amp panel typically operates on 240 volts, which is the standard for residential electrical systems in the United States.

Q: How do I calculate cable amp size?

A: Cable amp size can be calculated by adding up the total wattage of the devices on the circuit and dividing that by the voltage of the system, typically 120 or 240 volts. Once you have the required current or amps, you can refer to a wire size chart to determine the correct wire gauge for the circuit. It’s always best to consult a licensed electrician for assistance with any electrical project.


  1. https://www.nfpa.org/~/media/Files/Code%20or%20topic%20fact%20sheets/NECAmpacityWorkflow.pdf

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Rob Orr

Me and my family have lived through a nightmare of a remodeling project gone wrong, making countless mistakes including placing trust in the wrong hands. Despite these setbacks, we took matters into our own hands for many aspects of the remodel, ensuring quality workmanship guided by expert advice. Through my personal experiences, I've created RemodelReality.com. My mission is not only to share the pitfalls we encountered but also the successes we achieved by combining our efforts with trusted professionals. By sharing both the highs and lows of our journey, I aim to help others navigate their own remodeling projects with greater confidence, ensuring they benefit from our lessons learned.

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