@ volumizer
I am not sure exactly what good is the testing that was done in the link you provided.
The white paper did not address anything about a voltage that may/will be induced onto the equipment grounding conductor using the 12/3 with ground cable from the two current carrying conductors. Therein the Hot and neutral current carrying conductors. Any voltage on the equipment grounding conductor may/can cause a ground loop and hum.
It all has to do with the way the cable is designed/constructed.
Also worth noting allowing the third insulated conductor (red insulated conductor) to float above ground could have two effects. For one it may have an induced voltage placed on it from either of the hot or neutral current carrying conductors which then may induce a voltage onto the equipment grounding conductor. Second the floating above ground insulated wire may act as an antenna.
Here is a white paper from a well respected EE.
https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdfSee page 16. Read pages 31 thru 36.
As for the use of a 3 wire + ground cable here is a quote from a white paper from Middle Atlantic Products. The Company is now owned by Legrand.
AC Power Wiring Types (cont’d)
Metal Clad (MC) is manufactured in both steel and aluminum with twisted conductors that help reduce AC magnetic fields. Although the steel jacket helps reduce AC magnetic fields, the twisting of conductors has the greatest effect on reducing these fields. Another benefit is the constant symmetry of the phase conductors with respect to the grounding conductor which greatly reduces voltage induction on the grounding wire. (NEC article:330)
Two conductor plus 1 ground MC (Metal Clad)is a good choice for Non-Isolated Ground A/V systems. MC cable contains a safety grounding conductor (wire). The three conductors in the MC cable (Line, Neutral and Ground) are uniformly twisted, reducing both induced voltages on the ground wire and radiated AC magnetic fields. The NEC article 250.118 (10)a prohibits the use of this cable for isolated ground circuits because the metal jacket is not considered a grounding conductor, and it is not rated for fault current.
Two Conductor plus 2 ground MC (Metal Clad)may be used in an Isolated Ground installation, because the cable contains two grounding conductors (one for safety ground and one for isolated ground). The conductors are twisted, but the average proximity of the hot conductor and the neutral conductor with respect to the isolated grounding conductor is not equal. Under load, this will induce a voltage along the length of the isolated ground wire, partially defeating the intent of isolation (see Ground Voltage Induction section of this paper)
https://info.legrandav.com/l/71782/2018-12-14/7zh25n
Note the third paragraph. Same principals would apply for 3 conductor plus ground cable.
Though the quote is for MC (Metal Clad Cable) the same tests hold true for NM sheathed cable. (Romex is a Trade Name of NM cable).
Also note the chart on page 13 for the best type of wiring and method to use.
EDIT:
For those that think they need to use an IG (Isolated Ground) type grounding duplex receptacle.
Quote from Middle Atlantic Products white paper link above.
Armor Clad for Healthcare Facilities
(AC-HCF) Aluminum Armor Clad for Healthcare Facilities (AC-HCF) is the best choice for Isolated Ground A/V systems. Like MC, it contains an additional grounding conductor, although with this type of cable it is permissible to use the metal jacket as the safety grounding conductor, as required with isolated ground installations. The biggest benefit is that the average proximity of the hot conductor and the neutral conductor with respect to the isolated equipment grounding conductor is nearly equal, virtually eliminating ground voltage induction (GVI), even on long runs.
Steel Armor Clad for Healthcare Facilities (AC-HCF) Similar to aluminum armor clad AC-HCF, but does not address ground voltage induction as effectively as aluminum(see Ground Voltage Induction section of this paper). Two other problems are that steel clad is not readily available and is cumbersome to transport and install.
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