2011 NEC, 250.118 (10) undersized ground conductor ???

[MasterTheNEC]

Here's where my confusion started ..... RMC, IMC, EMT can be used as equipment ground conductors per 250.118 (2), (3), and (4). So, the way I see this, if I have a feeder that would require a #2 EGC, and I am using EMT conduit, the EMT conduit would be equivalent to the #2 EGC and there is no need to install a EGC inside the conduit. Now, in 250.118 (10), talks about using the combination of the metallic sheath (or armor) with the EGC in the mc cable to act as one EGC. Neither RMC, IMC, nor EMT need to be in "combination" with a EGC to be used as an equipment ground conductor type. So, in my mind, IF the EGC inside the mc cable is already good in size and meets T250.122, why do we need the mc cable to be listed as a equipment ground type if the EGC inside the mc cable is good enough? That's pretty much it....

@Ranger86 -

Please read 250.118(10)(a) through (c) again........

a. is referring to the standard practice of including a wire type EGC in the cable which would be sized per T 250.122.
b. is referring to the MC-SG or MC-AP where the equipment grounding/bonding conductor (which has served it's purpose at connector termination and can be cut off) is described here.
c. is referring to the options of Smooth or Corrugated Type MC...which we do not produce......

In your example the 2 AWG is installed in the raceway then it needs to be sized in accordance with T250.122...regardless. All that Section 250.122 is saying in item(4) is that it is not needed....also based on the 1993 Grounding Study Initiated at Georgia Institute of Technology project that shows the effectiveness of RMC,IMC and EMT as EGC's.....