Wire Size For 400 Amp Service: Complete Table And Chart

Discover the right wire size for a 400 Amp service – crucial for industrial, institutional, and commercial structures. We’ll guide you through selecting the optimal wire gauge, considering factors such as temperature and material, to ensure a safe and efficient electrical setup.

The best wire size for a 400 amp service is 1,000 kcmil aluminum or 400 kcmil gauge copper wire considering 167°F overload. However, if you are going for 140°F underground wiring, then use 1,250 kcmil aluminum or 600 kcmil gauge copper wire.

There will be a change in the wire size depending on various factors like the wire material, distance, voltage drop, temperature, and power lines running overhead or underground. This guide will share details about the 400 amp service, wire sizes, and installation cost. 

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What is the right wire size for 400 amp service?

The right size of wire for a 400 amp service is 1,000 kcmil. 

But, the actual size varies depending on various factors. 

These factors will determine the right wire size for a 400 amp service. 

Wire material

There are multiple wire materials, but the three most used wires for electrical purposes are:

  • Copper
  • Aluminum
  • Copper-clad aluminum

Copper wires are the most favored wires for electrical purposes. 

They are higher in conductivity, heat resistance, corrosion, and strength. 

The wires can carry enough current for longer distances without getting overheated. 

You can use the wires in whatever way you want because there is no fear of breakage. 

Besides, the wires have a green tarnish layer called Patina, which gets oxidized if the wires are exposed for longer periods. 

That will save the wire from corrosion without affecting the wire. 

On the other hand, aluminum wires are not that good in conductivity, resistance, or corrosiveness. 

Aluminum is good for shorter distances, cheap, and lightweight. 

Another is copper-clad aluminum. 

It has better conductivity, resistance, and corrosiveness than aluminum wires but is not as good as copper. 

So, depending on these features, the wire size differs due to the material quality. 

The right size of copper wire for a 400 amp service is 600 kcmil. 

You can also use a 1,000 kcmil copper wire, but 600 kcmil will easily manage a 400 amp service. 

But the right size of aluminum or copper-clad aluminum wire would be 1,000 kcmil. 

Distance and voltage drop

If the distance is longer, the wire has to be longer too. 

In that case, long wires will have higher resistance and overheating. 

To reduce the overheating chances, you have to use a higher gauge. 

Along with the resistance, the voltage drop will also increase. 

It would be best to have a higher gauge to handle the voltage loss to reduce the voltage drop. 

A standard voltage drop rate is 3%. Sometimes, it can rise to 5% due to the distance, but it should stay within 5%.

So, you need a thicker wire for longer distances.


Temperatures can highly change the wire size to 400 amps.

1,000 kcmil aluminum wire is considered the right wire size for 400 amps. 

But generally, this wire size can carry currents up to 500 amps when the temperature is at 167°F. 

But, when the temperature reaches 194°F, the amperage rate drops to 455 amps. 

That is why 1,000 kcmil aluminum wire is preferred for 400 amps.

A 600 kcmil copper wire can tolerate up to 475 amps at 167°F. 

But, when the temperature rises to 194°F, the amperage rate will drop to 400 to 340 amps. 

A 1,250 kcmil wire will be enough for a high power supply. 

The average amperage rate for 1,250 kcmil will begin above 400 amps. 

But, the lowest range of 1,250 kcmil copper wire will be 405°F if the temperature is around 194°F.

At 167°F overload, use 400 kcmil copper wire or 1,000 kcmil aluminum wire. 

For 140°F underground, use 600 kcmil copper wire or 1,250 kcmil aluminum wire. 

3-phase service

If you have a 400 amp 3-phase service, the wire will have few changes than the usual size. 

You can use 600 kcmil copper wires or 1,250 kcmil aluminum wires, especially at 140°F underground. 

Overhead and underground

The overhead and underground power lines are quite different, and so will be the wire sizes for 400 amps. 

For overhead power lines of 400 amps, you should use a 1,000 kcmil aluminum wire or a 400 kcmil copper wire. 

For the underground services, you can use a 1,250 kcmil aluminum wire or a 750 kcmil copper wire. 

Some good wire maintenance kits are:

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How do you determine the breaker size for 400 AMP Service?

To reduce the chances of any electrical accidents, you must have an ideal breaker size along with the wire. 

You also must verify the amp requirements of the appliances before installing the service. 

First, calculate the load to get the right breaker size after knowing about the total ampacity of the appliances. 

You must also determine the wire size based on the breaker capacity. 

Let us assume that refrigerators, dishwashers, and washing machines can run at 10 amps. But a microwave requires 20 amps. 

The circuit breaker amp must handle 125% of the load. 

The ideal breaker size would be 10 amp x 125%, which is 12.5 amp. 

This way, find out the amps of your household appliances and calculate the load to find the right breaker size. 

Some good circuit breakers are:

What size of ground wire do you need for 400 amps?

A ground wire is a wire that does not carry any current. 

When a short circuit occurs, the current takes an alternate path to flow. 

The current will flow through the ground wire if you have a grounding. 

If not, you receive a current shock. 

Since the wire is not used unless there is a short circuit, you can go for lower gauges. 

According to the NEC (National Electric Code), a 3 AWG copper wire and a 1 AWG aluminum wire is preferred for 400 amps ground wire. 

There are fewer chances of short circuits if you use the right wire size. 

But since the service is too high, the electricians will install it with full security and reduce the chances of ground wire. 

However, it is better to have the right ground wire size to be safe. 

What size of conduit do you need for a 400 amp service?

For a 400 amp service, you need a 3-inch conduit. 

The conduits are the home of the wires. 

They protect the wires from all kinds of physical damage, especially when they are run underground. 

Two conduits are used, especially for the underground services – PVC Schedule 40 and Schedule 80. 

Schedule 40 is white and thin and used in most installation procedures. 

You can also use Schedule 80. 

It is gray and thicker, which makes the conduit resist high pressures. 

When do you need to upgrade the electrical service?

Though a 400 amp electrical service carries enough current to power a whole factory, a standard US house will not require such high services. 

You require this when your house has many electrical appliances, like heating devices, air conditioners, hot tubes, jetted tubs, saunas, dishwashers, washing machines, etc. 

In that case, you must upgrade your house’s electrical service and install a 400 amp service. 

Otherwise, 150 to 200 amps are enough for every standard US home. 

If the electrical service of your house does not carry enough current and gets overloaded due to the functioning of multiple devices, the service will face issues. 

The breakers will keep tripping, and the wires will get overheated. 

You can see the tripping, dimming, flickering, and blowing off of the lights and bulbs. 

Tripping can also occur due to buzzing or sparking, which can lead to fire hazards in the future. 

You can understand the current load by calculating the amp rating. 

You need a flashlight and a calculator. 

How to understand the need for upgradation?

The flashlight will help to find the circuit panels as they are mostly in hidden areas like attics or basements where the children cannot access them. 

Open the panel door by unscrewing it. Wear protective gloves while dealing with electricity. 

Once you open the panel door, you will find the breaker. 

Look at the single and multi-pole breakers and write down the amp rating of each breaker. 

Do not include the rating of the main breaker. 

After writing down the amps, add them and multiply the result by 80%. 

You will find the total amp of your panel. 

It will tell you whether the electrical service of your house is enough or if you need a high amp. 

Most houses do not need such high-amperage electrical services. 

A 400 amp is usually used in bigger companies that use multiple heavy appliances. 

How much will it cost to install 400 amp electrical service?

There is no exact cost to install a 400 amp service as it is based on various factors like the location, work challenge, wire cost, conduit cost, distance, etc. 

Some utilities will do everything required, including lending equipment for free, needed during the installation. 

Others will want the full price. 

Since the job is quite critical, you need to hire a licensed electrician to do the job. 

They will do everything perfectly without causing any damage or mistakes.

The electricians will also tell you whether you need any current transformer or not. 

They will contact the local authorities for permission. 

The labor charges may cost around $500 to $800. 

The extreme can reach up to $3,000.

Per-hour labor charges are $50 to $100. 

Other expenditures will increase the price. 

Cost ComponentEstimated Cost Range ($)
Labor Charges$500 – $3,000
Per-Hour Labor Charges$50 – $100
Electrical Panel and Wiring$600 – $2,500
Conduit InstallationVaries (linear foot cost)
Trenching Costs$8 per linear foot
Conduit Costs$12 – $17 per linear foot
Equipment Rental (if needed)$300 – $500
Total Installation Cost$2,000 – $4,000 (varies by location and other factors)
Estimated Costs for Installing 400 Amp Electrical Service

For example, an electrical panel and wiring will cost around $600 to $2,500. 

An electrical panel to replace a fuse box can cost up to $2,000. 

If you wish to run underground services, that will increase the cost to a great level because of trenching and conduits. 

Trenching costs $8 per linear foot, and conduit costs $12 to $17 per linear foot. 

Trenching machines can cost $300 to $500 to rent. 

In short, a 400 amp service installation costs can range between $2,000 and $4,000. 

Since the cost varies, some homeowners pay around $3,500 to $4,500.

What is the danger of using the wrong wire size?

There is no danger in using wires thicker than the recommended size for 400 amp service. 

A thicker wire means:

  • Loads of electricity without any overheating or overload
  • You can use it for longer distances
  • The voltage drop will not cross 5%
  • The breaker will run smoothly

But never go for the thinner wires. 

A wire lower than the recommended wire size for 400 amps. 

Thinner wires cannot tolerate the amount of current that flows in a 400 amp service. 

The wires can melt, burn, and create a fire hazard. 

So, either use the right wire size or go for thicker wires. 

The thicker the wire, the better. 

What is the NEC Volts-Ohm’s Law for a 400 amp electrical service?

According to the NEC (National Electric Code) Volts-Ohm’s Law, the maximum voltage drop across a wire will equal 3% plus four-tenths of 1% times the square root of the total current in the amp.

VD (%) = 3% + (0.004 * √I)

It indicates that running a larger wire will be very costly if you use a small amount of power per foot. 

But, if you double or triple the power load per foot, you can receive more energy-efficient options. 

Finding the right wire size for your service may take time and effort. 

So, you must use the NEC-compliant electrical calculator or hire a licensed electrician before you decide on the wire for your service. We have added a calculator below for your convenience. You can try this out or even visit the NEC site for the same.

NEC Voltage Drop Calculator for 400 Amp Service

NEC Voltage Drop Calculator for 400 Amp Service

Calculate Voltage Drop for a 400 Amp Electrical Service:

Voltage Drop Percentage: %

The NEC rules have mentioned every wire size for all electrical services. You can follow them.

If you have any local codes that are different from the NEC codes, prioritize the local codes and ignore the NEC codes. 

The local codes are more important than NEC. 

A table of different wire sizes for 400 amps service

This chart will help you learn about the different wire sizes depending on the distance, phases, and material. 

Here, I have considered the maximum voltage drop to be 3%. 

Single phase

120V wire size

Distance in feetCopper wire sizeAluminum wire size
50 ft600 MCM900 MCM
75 ft600 MCM900 MCM
 100 ft600 MCM900 MCM
200 ft600 MCM900 MCM
 250 ft700 MCM1,000 MCM
300 ft750 MCM1,250 MCM

240V wire size

Distance in feetCopper wire sizeAluminum wire size
50 ft600 MCM900 MCM
75 ft600 MCM900 MCM
 100 ft600 MCM900 MCM
200 ft600 MCM900 MCM
 250 ft600 MCM900 MCM
300 ft600 MCM900 MCM

480V wire size

Distance in feetCopper wire sizeAluminum wire size
50 ft600 MCM900 MCM
75 ft600 MCM900 MCM
 100 ft600 MCM900 MCM
200 ft600 MCM900 MCM
 250 ft600 MCM900 MCM
300 ft600 MCM900 MCM


120V wire size

Distance in feetCopper wire sizeAluminum wire size
50 ft600 MCM900 MCM
75 ft600 MCM900 MCM
 100 ft600 MCM900 MCM
200 ft600 MCM900 MCM
 250 ft600 MCM900 MCM
300 ft700 MCM1250 MCM

 240V wire size

Distance in feetCopper wire sizeAluminum wire size
50 ft600 MCM900 MCM
75 ft600 MCM900 MCM
 100 ft600 MCM900 MCM
200 ft600 MCM900 MCM
 250 ft600 MCM900 MCM
300 ft600 MCM900 MCM

480V wire size

Distance in feetCopper wire sizeAluminum wire size
50 ft600 MCM900 MCM
75 ft600 MCM900 MCM
 100 ft600 MCM900 MCM
200 ft600 MCM900 MCM
 250 ft600 MCM900 MCM
300 ft600 MCM900 MCM

Final thoughts

The best wire size for a 400 amp service would be 1,000 kcmil aluminum wire or 600 kcmil copper wire. 

The wire size can change based on factors like the wire material, distance, voltage drop, temperature, and overhead and underground power lines. 

You need 3 AWG copper or 1 AWG aluminum wire for the ground wire. 

Copper wires are better than aluminum because they have good conductivity and heat and corrosion resistance. 

You need to use thicker wires if the distance is too long. 

That will lower the resistance and the voltage drop.

The cost to install depends on various factors. 

Sometimes, it remains within $2,000 to $4,000. And sometimes, the house owners end up paying $3,500 to $4,500. 

Related Articles:


Should you use ground rods for 400 amps service?

You need ground rods for 400 amps service. The distance between the two ground rods will be at least 6 feet. Use a 1/0 copper ground wire with a rod 4-6 below the grade.

Why will a house need 400 amp service?

Larger houses having too many heavy-duty appliances with more heating need a 400 amp service, for example, jetted baths, hot tubs, gyms, etc. 

Data Source: National Electrical Code, NEC Wire Table,  Electrical wiringHome wiring.

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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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