1. I did not say that one could run another wire in a cable. What I said that one could ADD an EGC conductor. The code always runing a completely separate conductor for this purpose.
From the NEC handbook.
"Section 250.130(C) applies to both ungrounded and grounded systems. It permits a
nongrounding-type receptacle to be replaced with a grounding-type receptacle under
the following conditions.
1. The branch circuit does not contain an equipment ground.
2. An existing branch circuit is being extended for additional receptacle outlets.
3. An equipment grounding conductor is connected between the receptacle
grounding terminal to any accessible point on the grounding electrode system, to any
accessible point on the grounding electrode conductor, to the grounded service
conductor within the service equipment enclosure, or to the equipment grounding
terminal bar in the enclosure from which the circuit is supplied.
The requirement in 250.52(A)(1) does not permit this separate equipment grounding
conductor to be connected to the metal water piping of a building or structure beyond
the first 5 ft of where the piping enters the building or structure unless the conditions of
the exception to 250.52(A)(1) can be met.
Exhibit 250.49 shows a branch-circuit extension made from an existing installation.
This method is also permitted to ground a replacement 3-wire receptacle in the existing
ungrounded box on the left, where no grounding conductor is available."
If the attachments works you will see the illustration from the NEC Handbook, "Exhibit 250.49 Branch-circuit extension to an existing installation, per 250.130(C),
illustrating a separate equipment grounding conductor connected to the
grounding electrode system."
A SEPARATE GROUNDING CONDUCTOR.
Type AC cable shall have an armor of flexible metal tape and shall have an internal
bonding strip of copper or aluminum in intimate contact with the armor for its entire
And from the NEC Handbook.
"The armor of Type AC cable is recognized as an equipment grounding conductor by
250.118. The required internal bonding strip can be simply cut off at the termination of
the armored cable, or it can be bent back on the armor. It is not necessary to connect it
to an equipment grounding terminal. It reduces the inductive reactance of the spiral
armor and increases the armor's effectiveness as an equipment ground. Many installers
use this strip to help prevent the insulating bushing required by 320.40 (the ``red
head'') from falling out during rough wiring."
AC cable meets the requirement for use as an EGC. There is no 6ft limit.