What Size Wire for 400 Amp Service (Full Breakdown)

A 400 Amp Service reflects the capacity of your electrical service which is usually measured in amps.

A 400 amps service demands a higher volume of current to flow through the wire. So, the size of the wires used in such a home or facility (with a 400 amperage rating) matters a lot. The presence of electrical appliances and other devices that utilize more power require a 400 amp service.

After being actively involved in many installations, I have noticed that most homes and facilities use the wrong wire gauge for 400 amp services. As a result, most have incurred losses due to fire breakouts and other faults. So, to avert such accidents, I am going to teach you what wires to use for a 400 amp service.

In General, the recommended AWG/kcml wire gauge for 400 Amp Service depends on the nature of the wires and the operational temperature.

  • For 167 degrees Fahrenheit overload, use an aluminum wire (1,000 kcml) or Copper wire (400 kcml).
  • And for 140 degrees Fahrenheit underground, use an aluminum wire (1250 kcml) and copper wire (600 kcml).

We will go into more detail below.

The Correct Wire Size for 400 Amps Service

400 Amp 3-Phase Service

For a 400 amp 3-phase service, you need a wire that can handle 400 amps.

Copper wires (600 kcml) and aluminum wires (1,250 kcml) are your best options – for 140 degrees Fahrenheit underground.

If you are wondering what wire size will suit a 400 amp service at your home, check the sections below.

167 Degrees Fahrenheit Overhead

An aluminum wire of size 1,000 kcml and a copper wire of 600 kcml can comfortably handle 400 amps.

140 Degrees Fahrenheit Underground

Here, you need an aluminum wire of size 1,250 kcml and 750 kcml copper cables for a 400 amp service.

Aluminum and copper wires of indicated sizes can comfortably contain a 400 amps rating.

blue insulated wire with bare copper tip

However, the AWG units will vary in different countries.

Why Do the Copper Wires Have Lower Values of Kcml?

Copper wires have lower kcml or AWG figures when compared to aluminum wires.

The most plausible explanation is the amount of resistance to the flow of electrons or electrical current. Copper has low resistance by virtue of its structural lattice whereas aluminum has high resistance.

How Much Money Do You Need for a 400 Amp Service?

400-amp service is usually available for homes with heating or cooling devices.

These devices use a lot of electrical energy. So, the service cost varies linearly with the amps rating – higher amperage costs more. That is why the maximum cost for a 100-amp service is $2,500. And that for 150 amps reaches $3,000.

The cost of a 400-amp service ranges from $2,000 to $4,000.  

On the other hand, the cost of 400 Amp installations ranges from $500 to $800, if you get lucky. If not, the cost can balloon to $3,000. And that excludes miscellaneous expenses – e.g. purchasing a new electrical panel and other wiring services which may cost about $600.

Fuse box replacements cost up to $2,000.

Do Homes Require 400 Amp Service?

A 400 amps rating is high. It is therefore required for homes with more heating and large air-conditioning capacity – homes with heating and cooling devices.

Homes that utilize hot tubs, jetted tubs, saunas, or any other appliances that require a lot of energy need a 400 amps service. (1)

electrician working on a big appliances

On the other hand, small homes without such devices do not need a 400 amp service. In most cases, 400 amp service is available in companies that use devices that consume more power.

How Does Wire Size Affect the Amps Rating?

It is imperative to understand that the size of the wire in your electrical fixture carries a certain amount of amps.

If the amp rating is too large for the wire, it can catch fire.

normal current rating in amps (table)

Logically, wires with larger diameters have higher amps ratings compared to those with smaller diameters.

The reason being the larger diameter of big wires offers more surface area for the flow of electrons. Since it is the electrons that convey electrical current, they end up ferrying more current and thus have a higher amps rating. (2)

The smallest size of a household wire can carry 15 amps of electrical current.

Dangers of Using the Wrong Wire Sizes for Various Amps

Always use the correct wire sizes for the given amperage.

Inaccurate wire size can extensively damage your electrical appliances and electronics. In some cases, fire may break out.

damaged outlet

Take your amplifier for example, if an inappropriate current flows to its circuits, it may get damaged. Additionally, its performance can drop if it receives the wrong voltage.

So, how do wrong wire gauges cause problems?

Since electrical current depends on the diameter/size of the wires, thinner wires experience more resistance as the current flows. If the amps are higher, the insulation coating may burn out resulting in a short-circuit.

Take a look at some of our related articles below.

(1) energy – https://www.britannica.com/science/energy
(2) electrons – https://www.space.com/electrons-negative-subatomic-particles

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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