What adjustment factor is applied to 4 pieces of 12/2 MC cable supplying 240-volt single-phase loads?

In calculating the adjustment factor for conductors like 12/2 MC cable, it is important to refer to the National Electrical Code (NEC), specifically Section 310.15, which provides guidelines on adjusting the conductor ampacities based on the number of conductors that are bundled together.

When four conductors are present in a raceway or cable assembly, the NEC specifies that an adjustment factor should be applied to account for the increase in temperature due to the heat generated by the current flowing through these conductors. For four or more conductors, the code indicates that the adjustment factor is 70 percent of the conductor's rated ampacity.

Applying this adjustment factor means that if each piece of 12/2 MC cable has a certain ampacity rating (for example, 20 amps for 12 gauge wire at 60°C), the effective capacity would be reduced to 70 percent due to the grouping of multiple cables. This ensures that the installation remains safe and that the conductors do not overheat under load conditions.

Hence, when considering the adjustment factor for four pieces of 12/2 MC cable supplying 240-volt single-phase loads, the application of the 70 percent adjustment factor aligns with NEC guidelines, making