What is the ampacity of three 12-2 conductor metallic cables, Type MC, grouped together?

To determine the ampacity of three 12-2 conductor metallic cables, Type MC, grouped together, it's essential to understand that ampacity refers to the maximum amount of electric current a conductor or cable can safely carry.

In the case of a standard 12 AWG (American Wire Gauge) wire, the typical ampacity under normal conditions is 20 amps. However, because the conductors are grouped together, there is a need to apply derating factors according to the National Electrical Code (NEC). When multiple conductors are bundled together, derating is necessary to account for increased heat buildup which can occur in grouped cables.

For three conductors, a typical derating factor of 80% is often applied. Therefore, the calculation for combined ampacity would look like this:

1. Start with the ampacity of a single 12 AWG wire, which is usually 20 A.

2. Multiply 20 A by 80% (or 0.8) due to the derating for grouping:

• 20 A * 0.8 = 16 A.

Since there are three conductors, you would take the higher value of individual conductor capacity or the derated capacity into account. For this