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 increases. This means that wires can carry less 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)

‘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)

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