Since you've written...
Ryan_J: That is code truth.... In my work, commercial, the AHJ has no problem with it. I, myself, cannot imagine how even a tyro is going to foul up such an install....
Roger: I agree entirely. IG receptacles don't get you anything in a residential application.
iwire: I run jobs for 'catfish' feeding at the bottom end of the commercial market. The IG, and associated contract specs, stops my bosses from screwing the owner on the ground path. ( And yes they would.--- I had to withstand a screamfest from two separate owner/ bosses on wasting green wire.) The requirement for dedicated ground clear to the panel provides the owner the pretext for testing it by lifting it off the isolated grounding bar.(And, yes...they do it. They've learned by experience.) Without this spec the owner would receive a system sending the ground path regular way: through the EMT -- linked to every hunk of metal on the way....
I have built raceways
under major high voltage lines ( inducing 270V on the skin of parked cars and a hefty induction to the T-bar over the sales floor. -- Lighting crews had to pre-ground the grid every time they worked on it from a lift.)
in the path of intense microwave radiation ( with all of the side lobes/ refections triggering voltage induction beyond 40V in the EMT. This had the fire alarm tech choking.
So it is true, for elements as small as microprocessor transistors, induced voltages in EMT -- found so irregularly in commercial situations -- you can't trust the EMT as a clean ground path.
And without the IG/ dedicated ground wire system the owner can't spot when the EC is cheating. And the pressure on the EC to cheat is intense since the bid was a crusher.
As electricians we are instructed from earliest days that impedence is purely an AC property. That is completely untrue. DC systems also exhibit impedence...but only during the transition to steady state conditions. And, in our customary work, that is all that we deal with. So, to get the test question right -- we answer no to DC impedence.
But, in the world of microprocessors, DC impedence is a huge design concern. A next generation of processor is being planned with additional layers expressly for the purpose of removing right angle turns on the DC ground path. Each bend in the current contributes to impedence. The exact number of conductors on the 80 pin disk drive ribbon connector dedicated to ground returns is 36 IIRC. (Every signal line gets one.)
The Code does not speak to this issue because the volts and energies are dramatically below any fire or health hazard.
iwire: the NEC will accept bonding through the raceway. There is abundant evidence that microprocessors can't live with that 'fault clearing path'.
One real world example: I have an RV -- and in that RV I have a PC -- and that PC is stand alone -- not even internet -- and when my propane igniter kicked in for hot water -- the PC locked up and crashed over and over. The solution was to change locations and clean up the grounding pin. Problem gone.
dereckbc has validity but speaks mainly to signal quality. Modern systems use error correcting data transmissions and operating system firewalls. The classic signal problems have been addressed.
Falling DC microprocessor bus voltages coupled to higher speeds drives the need for cleaner grounds.
All modern regulated power supplies have feedback mechanisms working at dramatically slower speeds than the microprocessor: 3 Gig. All of the DC loads are sunk to bonded common voltage (nominal 0 Volts) and the supply voltages are biased off of it through various schemes. If -- for even a moment -- a wave of DC/AC voltage surges up into the DC sink -- the microprocessor locks up entirely. This is the malady that has people pounding their keyboards.
I call it a 'DC return' because correctly wiring an IG causes it to exactly parallel the style and form of the AC return: the neutral. It is so much easier to explain it thusly to the troops. Neutral, they understand. Otherwise, my crew is bonding green wire all over and omitting the homerun.
"SDS in nature" does not compute. Spell it
out.
I am arguing very much in parallel to derekbc except that the "noise" that he declaims seems to be coming out of signals...in my experience the trouble almost always is from major circuit loads such as igniters, elevators, motors, contactors that trigger significant wave effect distortions ( think pulsed inductions ) on proximate ground paths. And, no the energy waves do not all immediately head into the GEC. They pour out onto all adjacent conductors until the wave sinks into the earth.
