Common 12-3 MC is easily used for IG circuits. The green is the IG, the white is N, the B (or R) is stripped back all of the way creating a code compliant bare dirty ground.
In the not uncommon situation of single phase clean power -- the hot can stay on color.
This avoids ordering trick IG 12-2 MC.
I explain IG as a DC return: It is wired up just like a neutral. The typical systems demanding IG in modern specs have internal DC power supplies producing regulated DC. The a sweet DC path is part of their voltage control logic.
As new chips are moving to ever lower voltages and 3,000,000,000+ cps any spikes -- on the DC could/ should cause errant logic. The power supply can't begin to adjust in the time frame of the microprocessor.
Bad grounds ( ground impedence ) are such a problem for modern systems that it is routine to design in waves of parallel grounds throughout cables and motherboards.
The outward manifestation of such spurious voltages may be computer lock-up. In older, east coast headquarters there have been tales of headaches so bad -- while running just PCs and the like -- that the building was retrofitted with clean power and IGs. Problem gone. ( From a manufacturer's ad IIRC )
Once burned, twice shy...It is easier to over spec than chase down the ghosts. In the above story -- they spent a fortune before scoping the problem. That's is what is so costly about dirty DC returns.
