What Wire Size Is Needed For 100 AMP Service (Explained)

Electrical contractors recommend installing a 100 amp service in your home because it offers minimum electrical resistance. It enables you to use a maximum number of electrical appliances, including a dryer, general lighting, and other electrical outlets.

Calculating the exact value of the amp service for a newly constructed house seems tricky. Most people use general calculator tools for calculating this. After selecting the value of amp service, the next step is to figure out how much wire length will be suitable for a hundred amp home service.

Which wire size is good for 100 amp service?

If you are interested in upgrading your electrical system, you must know the exact wire size. Moreover, the wrong wire size can lead to the deterioration of your electrical system. For a 100 amp service, you can use a # 4 AWG copper wire. An aluminium wire of # 2 AWG or a copper cladding wire is also helpful.

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What can I run on a 100 amp service?

A 100 amp service is powerful enough to provide energy to a house of medium size. Moreover, you can operate various devices of 240 volts on a 100 amp service. A central cooling system also works efficiently on this value of amp.

What is amp service?

Amp stands for amperage which denotes the amount of electric current flowing in the wires of a household system. Over time, the requirements of amperage increased for a house. As the number of electrical appliances increased, the required amperage also increased.

The old houses which did not occupy an updated electricity system operate on a 30 amp value but a new home with a modern and upgraded electricity system needs 400 amperes. It also depends upon the number of electrical outlets and central cooling systems working in households. In old times, the absence of dishwashers, microwave ovens, and refrigerators reduced the required amperage.

How to determine the amp service for your home?

Now you have a complete idea of ampere or amp service. It’s time to figure out the formula for calculating the amp service of your home. Knowing the amp service in your home is mandatory for making an upgrade.

The simple process to find the electrical service in your house is to get an overview of the primary components in your electrical system. It means you need to check the following parts:

  • The wire.
  • The panel.
  • The meter.
  • The conduits.
  • The primary breaker.

Find out the lowest value of amp for any of these components. It will be the amp service of your house. The amperage rating gets affixed by the manufacturer on any part. So, you can look at your panel to know this value. However, in some cases, if the panels get installed for the first time, you will need an inspector to check the amp value. The amperage of the main breaker is usually available on its front side or its adjacent side. However, the amp value of fuses is available on the backsides or the electrical panel.

What is AWG or Kcmil?


AWG is the abbreviation of American wire gauge. Brown and sapphire wire gauge is another name for this.

AWGG is a logarithm-based wire gauge system usually used in North America. Since 1857, the AWG system has helped estimate the sizes and the radii of the round-shaped and solid wires. It also helps to analyze the diameter of a conducting wire.


Thousands of circular mils help us determine the diameters for all the wires above the AWG 4/0. Keep in mind that 1 Kcmil is equal to 0.5067 mm². A circular mill stands for the area of a conducting wire having a diameter equal to one mil.

Although these terms are very technical, knowing the basic meaning of these terms can be helpful to you in upgrading your electrical setup. Moreover, having the know-how of the system is also necessary to get the perfect wire size.

What are wire sizes helpful for making amp upgrades?

Here is a complete chart that indicates the required wire sizes for different values of amp services. The purpose of mentioning these wire sizes and AWG values is to help you in case you need to upgrade the amp service.

Table for different amp services and different conductors.

Service or feeder ratingCopper conductorsAluminium or copper cladding conductorsMinimum conduit size
100 Amps#4 AWG#2 AWG1 ¼ inch
125 Amps#2 AWG#1/0 AWG1 ¼ inch
150 Amps#1 AWG#2/0 AWG1 ¼ inch
200 Amps#2/0 AWG#4/0 AWG1 ½ inch
250 Amps#4/0 AWG300 kcmil2 inch
300 Amps250 kcmil350 kcmil2 ½ inch
400 Amps400 kcmil600 kcmil3 inch

Copper vs. Aluminum. Which wire would be best to buy?

As you have gotten information on the appropriate wire size for your 100 amp service, you must know the wire material which could be best for upgrading. Aluminium wires have less conductivity of electrical current. So, these wires must have a large size to provide enough electricity.

Aluminium also corrodes, so there is a need for proper preparation to protect it from corrosion at the terminal ends. You need to apply an antioxidant or any other paint to prevent rusting or corrosion. However, the aluminium wires having copper cladding do not undergo rusting.

The best thing about aluminium wires is that they are cheaper than other conductors. Being light in weight is another plus point of this material. The flexibility of these wires also adds more value to their efficiency.

Why are copper wires most likely to be used?

However, copper wires are the best conductors due to their minimum resistance. So, every wire has its pros and cons, and you need to make an intelligent decision according to your requirements. Copper wire has maximum points due to the following reasons:


It can withstand heavy loads of current due to its minimum resistance.

Less resistance

Copper offers low opposition to the current. So, the maximum current can pass through it.

Usable at long distances

Due to its low resistance, it is usable at very long distances. Copperworks efficiently at long distances due to its premium conductivity and heat resistance properties.

No need for a protective coating

There is no need for any insulation or protective coating for copper wires. The reason is that copper does not undergo corrosion. The oxidation of copper produces patinas, but it does not affect the conductivity of the copper.

Lesser wire gauge

The lower wire gauge of copper works very efficiently as compared to aluminium. Nearly half of the wire gauge required for aluminium is enough for a copper wire.

Heat resistant

It is also heat resistant and therefore offers minimum resistance. The connection of the wire does not get loose because copper does not undergo expansion or contraction with an increase in heat.


Copper is more malleable than aluminium. So, this helps the people to use copper wire of a small wire gauge.

Plus points of an Aluminum or copper-clad aluminum wire

Following are a few reasons that make this wire more usable:


Aluminium wire is cheaper in terms of price. It is more affordable than copper and copper-clad wire. However, the plus points of copper do not undermine the significance of aluminium because it demands a very minimum investment.

Easy installation

Moreover, the installation of aluminium wire is also easy. Faster installation and lower labour costs make it the favourite of electricians.

How many wires are mandatory for a 100 amp service?

The type of wire gauge needed for a house also depends on the current load. The 3-wire cable coming out of the meter contains two hot conducting wires and one neutral wire. Electric fixers help make a connection between the neutral and ground bars.

However, the feeder cable has four wires. Out of these, two are conducting wires, one is the neutral wire, and the other is the ground. There is no need to connect between the neutral and ground bars.

Local electrical codes and permit requirements

The codes for the electrical system may vary according to the location. However, the national electrical code is the mainstream authority for electrical codes. If you hire an electrician who has the proper license and knows the terms or conditions of your area, you will meet the requirements. The electrical code of NEC changes from time to time or gets upgraded for improvements.

Electrical costs for installing a 100 amp service

There is no proper way to determine the costs for a 100 amp service at home. There are different, considerable factors to determine the installation costs like:

  1. Additional service charges.
  2. Distance from the meter box
  3. Location of installation.

Installing a 100 amp service requires the following components:

  • 100 amp sub panel.
  • 100 amp feeder wire.
  • Conduit.

So, the traditional costs made on the installation of a 100 amp service are 1500 $ to 4500 $. The average cost is 3000 $. This cost includes:

  • 100 amp electrical panel. The average cost for this component is 1000 dollars, and the price can vary from 500$ to 1500$.
  • 100 amp feeder wire. The cost for the feeder wire ranges from 1500 dollars to 3000 dollars, and the median price is 2000 $.

What is a voltage drop, and why is it important?

It is the value of the loss in voltage due to the resistance. The resistance to current gets offered by the wire. So, the greater the length of your wire, the greater is the voltage loss or voltage drop. There is a piece of simple information that the voltage on your main circuit meter is 120 volts. If you use a voltmeter (a voltmeter is a device used for measuring the voltage in a circuit), you will find that the voltage will drop as the distance from your primary circuit increases.

Electricians recommend that the voltage drop must not be greater than 3 % of your exact voltage. It means that the voltage after loss must not be less than 117 for a 120-volt circuit. If you have an external voltage of 240 volts, the voltage should not fall below 233. It means that you must maintain the voltage at this value. So, try to take different measures for maintaining the voltage at this value.

Role of service wire length

Determine the length of the wire from the circuit to the electrical panel. The length of the service wire also matters in deciding the size of the wire for 100 amp service. As you know, the permitted value of voltage drop is 3 %. So, you must analyze the material of the wire from copper or aluminium. Determine the length of the path travelled by the wire and choose between aluminium or copper accordingly.

What could be the wire distance for maintaining a 3 % voltage drop?

As you have gotten a complete sketch of the voltage drop, you must figure out the length of the wire from the mainstream circuit to the panel to maintain voltage. Here is a rule of thumb for determining the value of the wire for a 3 % voltage drop.

Rule of thumb

  • The length of a copper # 2/0 AWG must not be greater than 50 feet.
  • A 100 feet wire of copper is good with a # 3/0 AWG.
  • You can run a 50 feet aluminum wire having # 4/0 AWG.
  • An aluminum Kcmil wire must not be greater than 100 feet.


In addition to knowing about the wire size for a 100 amp service, you also need to have complete information on the following things:

  • How to figure out the amp service of your house?
  • What wire sizes would be essential in case of any upgrade?
  • What could be the minimum distance from your circuit to prevent a voltage drop greater than 3 percent?

That’s why we provided and added all this information in this article. If you give it a serious read, you will know the exact procedure and the requirements before hiring a professional. It will also help you prevent any extra investment and possible loss.

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