kcmil Wire Size Chart (Ampacity Of 250-2000 MCM Wires)

kcmil or MCM are considered bigger wires (bigger than AWG wires). We generally use these thick wires when we need more than 200 amp service. Which kcmil wire exactly we need for carrying high currents is determined by the kcmil wire size chart (check the chart further on).

Example: What is the ampacity of 400 kcmil copper wire? If you check the kcmil ampacity chart below, you can see that 400 kcmil copper wire has a 335A ampacity (at a median 75°C or 167°F temperature).

Let’s first clear a bit of confusion about kcmil and MCM wires since many homeowners think they are two different kinds of measures for wires. They are both abbreviations for the same thing.

Both MCM and kcmil abbreviate a unit called ‘thousand of circular mils’. A circular mil measured a cross-section of a wire. Circular mill is a very small unit – equal to 0.0005067 mm2 area – so we use ‘thousands’ of them in a unit like MCM or kcmil:

  • kcmil standards for ‘kilo circular mils’.
  • MCM stands for ‘thousands (M) of circular (C) mils (M)’.

Example: 400 kcmil wire has a cross-section equal to 400 thousand circular mils.

The key question kcmil wire size chart (which is the same as MCM wire size chart) answers is how many amps can a wire handle.

The ampacity (how many amps they can carry) of wires depends on 3 primary factors, namely:

  1. Cross-section. This is denoted by kcmil or MCM. We have 250 kcmil, 300 kcmil, 350 kcmil, 400 kcmil, 500 kcmil wires, and so on. The biggest kcmil wire is the 2000 kcmil wire.
  2. Metal used. Copper and aluminum wires are most commonly used. Same-size copper wires can carry a little more current than aluminum wires.
  3. Temperature. At higher temperatures, the resistance in the wires decreases. This means that wires can carry more current at higher temperatures (according to Ohm’s Law).

Ampacity depends on kcmil or MCM (units for cross-section), yes, but it also depends on metal used (copper vs aluminum) and temperature.

That’s why we have two separate MCM wire size charts (1st chart for copper wires and 2nd chart for aluminum wires). Here are both charts with ampacity for different kcmil wires at 3 different temperatures (65°C, 75°C, and 90°C):

kcmil Wire Size Chart (Copper Wire)

kcmil or MCM Wire: mm2 (Diameter): Ampacity At 60°C (140°F): Ampacity At 75°C (167°F): Ampacity At 90°C (194°F):
250 kcmil (250 MCM) 126.7 mm2 215 Amps 255 Amps 290 Amps
300 kcmil (300 MCM) 152.0 mm2 240 Amps 285 Amps 320 Amps
350 kcmil (350 MCM) 177.3 mm2 260 Amps 310 Amps 350 Amps
400 kcmil (400 MCM) 202.7 mm2 280 Amps 335 Amps 380 Amps
500 kcmil (500 MCM) 253.4 mm2 320 Amps 380 Amps 430 Amps
600 kcmil (600 MCM) 304.0 mm2 355 Amps 420 Amps 475 Amps
700 kcmil (700 MCM) 354.7 mm2 385 Amps 460 Amps 520 Amps
750 kcmil (750 MCM) 380.0 mm2 400 Amps 475 Amps 535 Amps
800 kcmil (800 MCM) 405.4 mm2 410 Amps 490 Amps 555 Amps
900 kcmil (900 MCM) 456.0 mm2 435 Amps 520 Amps 585 Amps
1000 kcmil (1000 MCM) 506.7 mm2 455 Amps 545 Amps 615 Amps
1250 kcmil (1250 MCM) 633.4 mm2 495 Amps 590 Amps 665 Amps
1500 kcmil (1500 MCM) 760.1 mm2 520 Amps 625 Amps 705 Amps
1750 kcmil (1750 MCM) 886.7 mm2 545 Amps 650 Amps 735 Amps
2000 kcmil (2000 MCM) 1013.4 mm2 560 Amps 665 Amps 750 Amps

‘Which temperature should I look for ampacity?’ This is one of the most common questions from people who see this kcmil copper wire size chart.

Basically, it depends on which type of wire you have. You should look at:

  • 60°C ampacity for these types of wires: TW, UF.
  • 75°C ampacity for these types of wires: RHW, THHW, THW, THWN, XHHW, USE, ZW.
  • 90°C ampacity for these types of wires: TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2.

The same goes for the MCM aluminum wires. You can find the ampacity chart for kcmil aluminum wires here:

kcmil Wire Size Chart (Aluminum Wire)

kcmil or MCM Wire: Ampacity At 60°C (140°F): Ampacity At 75°C (167°F): Ampacity At 90°C (194°F):
250 kcmil (250 MCM) 170 Amps 205 Amps 230 Amps
300 kcmil (300 MCM) 190 Amps 230 Amps 255 Amps
350 kcmil (350 MCM) 210 Amps 250 Amps 280 Amps
400 kcmil (400 MCM) 225 Amps 270 Amps 305 Amps
500 kcmil (500 MCM) 260 Amps 310 Amps 350 Amps
600 kcmil (600 MCM) 285 Amps 340 Amps 385 Amps
700 kcmil (700 MCM) 310 Amps 375 Amps 420 Amps
750 kcmil (750 MCM) 320 Amps 385 Amps 435 Amps
800 kcmil (800 MCM) 330 Amps 395 Amps 450 Amps
900 kcmil (900 MCM) 355 Amps 425 Amps 480 Amps
1000 kcmil (1000 MCM) 375 Amps 445 Amps 500 Amps
1250 kcmil (1250 MCM) 405 Amps 485 Amps 545 Amps
1500 kcmil (1500 MCM) 435 Amps 520 Amps 585 Amps
1750 kcmil (1750 MCM) 455 Amps 545 Amps 615 Amps
2000 kcmil (2000 MCM) 470 Amps 560 Amps 630 Amps

We hope that these two wire charts for big wires can help you with any project.

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