Equipment Grounding and Equipment Grounding Conductors
250.118 Types of Equipment Grounding Conductors
This subsection was completely revised to read:
(11) MC Cable. The outer metal sheath of smooth or corrugated tube type MC cable can serve as an equipment grounding conductor.Intent: MC cable is constructed in three different forms: (1) spiral interlocked metal sheath, (2) smooth metal sheath, and (3) corrugated metal sheath. The change to this section is intended to clarify that interlocked metal MC cable (looks like flexible metal conduit with wires installed in it) is not listed as an equipment grounding conductor and it must contain an internal equipment grounding conductor. The sheath of smooth or corrugated tube MC cable (rarely used) is suitable for equipment grounding and an internal equipment grounding conductor is not required within this type of cable.
What is the difference between interlocked MC cable and interlocked AC cable? Interlocked armored cable is manufactured with an internal bonding strip of aluminum in direct contact with the metal armor. The combination of the bonding strip and the armor makes the cable suitable as a fault current path, and an equipment grounding conductor is not required within the cable. The metal armor of interlocked MC cable alone is not suitable as a fault current path (no bonding strip), therefore an equipment grounding conductor is required within the cable.
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