What is MC cablein construction?

MC stands for metal clad. An MC cable is a factory assembled wiring product whose insulated circuit conductors and grounding conductor are protected by a flexible interlocking metal armor; the NEC covers it under Article 330. On drawings and in estimates it appears as a configuration callout such as 12/2 MC, read as two 12 AWG conductors plus ground in metal clad armor.

Usually yes on installed cost for branch circuits, because the labor to route and support cable is much lower than bending conduit and pulling conductors, even though MC material can cost more per foot than EMT plus wire. The advantage shrinks on short runs with few bends and disappears where the spec requires conduit anyway. Price both options on long repetitive branch work; the spread is often the difference between winning and losing the electrical bid.

Both are armored cables, but standard MC cable carries a full size insulated equipment grounding conductor inside the armor, while AC cable (often called BX) uses its armor with an internal bonding strip as the grounding path. The NEC covers them under separate articles (330 for MC, 320 for AC) with different permitted uses. Commercial specs commonly accept MC and reject AC, so read the spec before treating them as interchangeable.

The NEC permits MC in most locations, but project specifications routinely restrict it further: many commercial specs limit MC to concealed branch circuits in dry locations and require conduit for homeruns, exposed work, exterior or wet locations, and anywhere subject to physical damage. Standard MC is also not rated for wet locations or direct burial unless specifically listed for it. The spec section, not just the code, decides what you can carry in the bid.