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This is The Wire Size You Need For 400 Amps!

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Before now, most houses ran their electrical weight on a 100- or 200-amp service.

But, with the constant need for electricity for household appliances, the preferred service is now 400 amps.

This service has an efficiency of 80 to 85%, which makes it ideal for large households. Due to the high current volume, the service requires wires to support the electrical flow.

Therefore, using the proper wire gauge can prevent mishaps like burning appliances and fire breakouts.

The wire size needed for a 400-amp service varies depending on the wires’ material and the operation’s temperature. For example, at 167°F, the ideal aluminum wire size is 1000 kcmil, while that of copper is 400 kcmil. When the temperature drops to 140°F, the required wire size increases to 1250 kcmil and 600 kcmil for aluminum and copper, respectively. 

What Wire Size Is Good for 400 Amps?

What Wire Size Do I Need For 400 Amps

Like most electrical circuits, copper or aluminum is the best wire type for a 400-amp service. However, different sizes of these wires depend on the circuit’s operational temperature.

For example, a 1000 kcmil aluminum wire can carry up to 500 amps of power at 167°F.  However, at 194°F, the amperage range drops to a minimum of 455 amps.

On the other hand, a copper wire measuring 600 kcmil has the lowest amperage range of 475 amps at 167°F. The range drops below 400 to 340 amps at 194°F, just like aluminum.

However, wires with 1250 kcmil have enough accommodation for a high power supply. However, their amperage starts way above 400 amps. The lowest range is copper at 194°F has a range of 405 amps.

The table below summarizes wire sizes for both materials at different temperatures.

Wire MaterialWire Size140°F167°F194°F
Copper500 kcmil320 amps380 amps430 amps
600 kcmil355 amps420 amps475 amps
Aluminum1000 kcmil375 amps445 amps500 amps
1250 kcmil405 amps485 amps545 amps

When it comes to wire gauging, the higher the size number, the smaller the diameter of the wire. There are two gauging systems for wires.

These systems are the American Wire Gauge (AWG) and the circular mils (kcmil). These circular mils wires are also called MCM wires.

The MCM wires are more prominent and thicker than AWG wires. The latter wires are used when the service is less than 200 amps.

The minor MCM wire measures 250 kcmil and can go as high as 2000 kcmil. When buying wires, it is paramount to be sure of the kind of wires that you buy.

Buying and using the wrong wires or gauges during installation can be hazardous.

The first effect of using the wrong wires or gauges is the wires will melt because of the high current supply.

This heating can eventually lead to fire outbreaks. It is not cost-effective at a minimum, as you will have to pay for the correct reinstallation.

To be on the safe side, it is better to overestimate your circuit capacity than to underestimate it.

When Do I Need to Upgrade to a 400-amp Service?

Despite its ability to carry a lot of electrical power, the 400-amp service is not compulsory for all households.

You only need this service connection if the appliances in your house weigh so much on the current supply.

You should upgrade your service if you have heating appliances or cooling systems like air conditioners.

Examples of appliances with tasking electrical weight are dryers, hot tubes, saunas, jetted tubs, washing machines, dishwashers, etc.

If your electrical current is overloaded, you will encounter some problems. These problems are frequent tripping and overheating of the breakers and wires.

You can notice the tripping in flickering, dimming lights, or light bulbs blowing up frequently.

This tripping can also cause sparking or buzzing in the panel. Over time, these sparks can lead to fire hazards and outbreaks.

You can determine the load of your circuit by calculating your amp rating. You will need flashlights, calculators, and writing materials to do this effectively.

The flashlights are essential because circuit panels are usually placed in secluded areas. These areas, like attics and basements, are not always accessed by children.

When you find the circuit panel, open the panel door by unscrewing it. Remember that you should always wear protective gear when working with electricity.

Once it opens, it will expose all the circuit breakers. Be sure to pay attention to the single- and multi-pole breakers and write down the amp rating of each one.

When observing, do not include the main breaker at the top or bottom of the panel. Once you have written down all the amps on the breakers, proceed to add them.

Then, multiply the value you get by 80%. The result is the total amperage in your panel. Knowing this will help you determine if your service is well-loaded or if you need an upgrade.

What Wire Size Do I Need for a 400-amp Underground Service? 

The wire size for an underground service is the same as an overhead power service.

Factors like temperature and the nature of conducting material will influence your choice of the wire size. Both aluminum and copper are as suitable for underground and overhead services.

Underground service, as the name implies, means that the wires are connected directly from the utility company to your house through an underground pipe.

There are several advantages of the underground connection over the overhead service. With underground service, all the wires are neatly buried.

Doing this protects the wires from destruction due to storm breaks or other weather inconsistencies.

Underground connections are also aesthetically pleasing as there are no errant poles everywhere. The major disadvantage of this type of connection is that it is more expensive than overhead.

Statistics show that installing underground service cost about five times more than overhead connections.

Another disadvantage is that you cannot dig in areas with underground installations.

What Conduit Size Do I Need for a 400-amp Service?

One of the requirements to install a 400-amp service is a 3-inch conduit. Other requirements are a big current panel box and another box for the circuit breaker.

The conduits serve as housing for the wires. Two types of conduits are used during this service installation, primarily underground.

These conduits are Schedule 40 PVC and Schedule 80 PVC, also known as Sch 80 PVC and Sch 40 PVC.

The Schedule 40 PVC is white and thinner and is used in most parts of the installation process. However, there are a few exceptions to this rule.

These exceptions are: 

  • If the wires will pass under a roadway.
  • From the last elbow of the connection to the meter base.
  • The first 10 inches of exposed conduit before it goes underground from the transformer pole.

In these scenarios, Sch 80 PVC is used instead. This conduit is gray and thicker than the other conduit. This thickness makes it possible for the conduit to resist high-pressure levels. 

What Copper Wire Size Do You Need for 400 Amps? 

The copper wire size you need for a 400-amp connection depends on the operational temperature.

At high temperatures like 194°F, the ideal wire size is 600 kcmil. Meanwhile, at low temperatures, the copper wire size is 500 kcmil

These values are about half of the aluminum. The reason is that copper wires have higher conductivity than aluminum wires of the same length.

Copper wires are mostly referred to as aluminum wires for many reasons. Some reasons are:

  • Copper has about 40% more tensile strength than aluminum which means it is less inclined to break under electrical pressure.
  • The thermal expansivity coefficient for copper is lower than that of aluminum. This means it has a higher resistance to higher electrical power flowing through the wires.
  • The high tensile strength and lower thermal expansivity conjoin to ensure the longevity of copper wires compared to aluminum.

On the other hand, copper does have some disadvantages, which include:

  • It is more expensive than aluminum.
  • Due to its higher tensile strength, copper is more rigid and heavier than aluminum.

These properties make copper more challenging to work with. Considering these advantages and disadvantages, one can say that the choice of wire depends on the nature of the job and the budget.


It is not compulsory to install a 400-amp service system in your house if your electrical load is small.

But, if necessary, it is better to employ the services of professional electricians. Doing this makes your safety conscious and reduces the chances of mistakes.

Therefore, you should endeavor to use trusted professionals who perform the correct installations for you.

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