400 kcmil (MCM) Copper and Aluminum Wire: The Complete Guide

400 kcmil (MCM) copper and aluminum wires are thick wires generally used for 200+ Amps (copper) and 150+ Amps (aluminum) service.

Actual 400 kcmil wire Ampacities depend on the wire material, if the wire is enclosed or suspended in air, maximum wire temperature, and similar.

Published: April 5, 2023.

400 kcmil (MCM) Wire Diameter and Cross Section Area

A circular mil equals the area of a circle with a diameter of one-thousandth of an inch (one mil) or 0.0254 mm, and it has a value of 5.067075×10⁻⁴ mm² (506.7075 μm²).

Thus, the 400 kcmil wire features an area surface of 202.683 mm², which is often shortened to 202.7 mm².

The diameter of 400 kcmil wire is ~16.06 mm or 0.632 inches - this is the diameter of a solid wire without insulation.

Since solid aluminum or copper 400 kcmil wires are rather hard to work with, 400 kcmil wires are mostly used as stranded wires with 7-37 or even more strands.

Such wires are somewhat thicker due to the air gaps between strands, but they are much easier to work with.

Generally, 400 kcmil/MCM wires with an insulation feature diameter in the 0.82-0.90 inches (21-23 mm) range.

400 kcmil/MCM Copper and Aluminum Wire Ampacity

Wire current carrying ability, also known as Ampacity, is given for the enclosed wires and wires suspended in air.

Also, Ampacities are given for three different maximum temperatures.

For example, the Ampacities for 400 kcmil copper and aluminum wires are given in the following lists:

400 kcmil Copper Wire Ampacity:

• @60°C/140°F: 280 Amps,
• @75°C/167°F: 335 Amps,
• @90°C/194°F: 380 Amps.

400 kcmil Aluminum Wire Ampacity:

• @60°C/140°F: 225 Amps,
• @75°C/167°F: 270 Amps,
• @90°C/194°F: 305 Amps.

These are the maximum allowed Ampacities, and they don't take into account any safety margin, which is usually the so-called "80% Rule" - actual Ampacities are 80% of the maximum Ampacities:

400 kcmil Copper Wire Ampacity (80% Rule):

• @60°C/140°F: 224 Amps,
• @75°C/167°F: 268 Amps,
• @90°C/194°F: 304 Amps.

400 kcmil Aluminum Wire Ampacity (80% Rule):

• @60°C/140°F: 180 Amps,
• @75°C/167°F: 216 Amps,
• @90°C/194°F: 244 Amps.

Now, the 80% Rule provides the safety margin, but it doesn't consider wire length and, thus, increased energy losses.

Generally, actual Ampacity drops by 10% for every 50 feet of the wire, requiring careful planning.

400 kcmil/MCM Wire Ampacity In Air

When the wires are suspended freely in the air, their Ampacities are increased due to the improved cooling. However, such wires may also receive additional heat in the form of sunlight and similar radiation.

For example, the Ampacities for 400 kcmil copper and aluminum wires suspended in air are given in the following lists:

400 kcmil Copper Wire Suspended in Air Ampacity:

• @60°C/140°F: 455 Amps,
• @75°C/167°F: 545 Amps,
• @90°C/194°F: 615 Amps.

400 kcmil Aluminum Wire Suspended in Air Ampacity:

• @60°C/140°F: 355 Amps,
• @75°C/167°F: 425 Amps,
• @90°C/194°F: 480 Amps.

Note: Before actual use, careful planning is required, taking into account safety and wire length.

As one can see, wires suspended in the air have much larger Ampacities than enclosed wires.

400 kcmil/MCM Wire Weight

400 kcmil wires are thick wires that often must be supported to prevent them from shifting and moving around due to their own weight.

400 kcmil Copper Wire Weight

With 202.7 mm² (2.027 cm²) cross-section area and a density of 8.96 g/cm³, 400 kcmil cooper wire without insulation weighs:

• 1 cm: 18.16192 grams = 0.01816192 kg = ~0.04 pounds
• 1 foot (30.48 cm): ~553.57 grams = ~0.5536 kg = 1.2205 pounds
• 1 meter: 1816.192 grams = ~ 1.816 kg = ~4 pounds

So, bare solid copper 400 kcmil wire weighs ~1.22 pounds/ft.

However, the actual weight of the 400 kcmil copper wire with insulation depends on the insulation and usually ranges from 1.3 to 1.5 lbs/ft.

400 kcmil Aluminum Wire Weight

With 202.7 mm² (2.027 cm²) cross-section area and a density of 2.70 g/cm³, 400 kcmil aluminum wire without insulation weighs:

• 1 cm: 5.4729 grams = 0.0054729 kg = ~0.01206 pounds
• 1 foot (30.48 cm): ~166.81 grams = ~0.16681 kg = 0.36776 pounds
• 1 meter: 547.29 grams = ~0.54729 kg = ~1.206 pounds

So, bare solid aluminum 400 kcmil wire weighs ~0.36776 pounds/ft.

However, the actual weight of the 400 kcmil aluminum wire with insulation depends on the insulation and usually ranges from 0.43 to 0.5 lbs/ft.

400 kcmil Wire Price

400 kcmil wires are not cheap, and their price depends on the wire type, wire material, construction (number of strands), insulation quality, etc.

Also, it is not the same if You purchase just a few feet of these wires or hundreds or even thousands of meters of wire.

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For wire gauge charts and more information about this topic, feel free to check our Wire Gauge Charts: AWG to mm2 Conversion Charts and Wire Sizes article.