Kdrifter, the difference in MC and AC is as follows. (From AFC)
Armored (Type AC) Cable Construction
As described by the National Electrical Code NEC® 2002 Article 320, armored cable Type AC is a “fabricated assembly of insulated conductors in a flexible metallic enclosure.”
Type AC cable is manufactured to UL Standard 4. It consists of 2 to 4 copper conductors in sizes 14 AWG to 1 AWG inside an interlocked metal armor of steel or aluminum construction.
Type AC cable can have no more than four insulated conductors plus a grounding conductor (for a total of 5 conductors only) and cannot be manufactured larger than 1 AWG per UL 4.
A 16 AWG aluminum bonding wire is inside of, and in physical contact with, the metal armor providing a low-impedance fault return path required for the operation of overcurrent protection devices. The bonding wire is unique to AC cable and allows the outer metal armor in conjunction with the bonding wire to be used as an equipment ground. It is important to remember that the bare bond wire is not an equipment grounding conductor. It is the bond wire that, in combination with the interlocked metal armor, provides a low impedance equipment grounding path. Each of the copper conductors is covered with a thermoplastic insulation (THHN with a 90°C rating) and are individually wrapped in a moisture resistant, fire retardant paper.
According to NEC Article 320.40, an insulated (anti-short) bushing is required when installing Type AC cable. It is installed at the time of termination and designed to protect the conductors from damage. AFC provides bushings in bags packaged with the cable.
Metal Clad (Type MC) Cable Construction
As described by NEC Article 330, Metal Clad Type MC cable is a “factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape or a smooth or corrugated metallic sheath.”
Type MC cable is manufactured to UL Standard 1569. MC cables may have 1 or more solid or stranded conductors in sizes 18 AWG and larger. The number of conductors allowed in an MC cable is not restricted by UL. The conductors may be of copper, aluminum or copper-clad aluminum.
The metal armor may be a smooth tube, a corrugated tube, or an interlocked metal armor. AFC Cable Systems manufactures MC cable with interlocked metal armor and copper conductors.
The make-up of AFC’s 600 Volt interlocked armor MC cable consists of:
• Copper circuit and grounding conductors
covered with thermoplastic insulation
• An overall polypropylene cable assembly tape
• An outer galvanized steel or aluminum interlocked armor
Unlike Type AC cable, the armor of interlocked Type MC cable is not an equipment grounding means and Type MC cable requires a bare or green grounding conductor.
Roger
[This message has been edited by Roger (edited 05-01-2005).]
