Reinforcing Ait's comment just above is the following statement on page 6 of this document by a noted expert on such matters, Bill Whitlock of Jensen Transformers:
In the case of a balanced interconnection, depending on the design of the specific components the cable shield may be connected to chassis, but in many designs it will (incorrectly) be connected to circuit ground instead.
Geoff, re your question, see page 8 of the reference I linked to above. And note this statement: "If multiple ground rods are used, Code requires that they all MUST be bonded to the main utility power grounding electrode." Otherwise, as explained in the paper, safety hazards may arise from both equipment faults and lightning strikes. Also note the statement on page 3 that some engineers (incorrectly) "think that system noise can be improved experimentally by simply finding a better or quieter ground. Many indulge in wishful thinking that noise currents can somehow be skillfully directed to an earth ground, where they will disappear forever!" The quality of the earth ground of the AC distribution system is unrelated to grounding issues that may arise within the system, that may affect sonics.
Regards,
-- Al
Consider two devices connected by a signal cable, each device having a 3-prong ac plug. One device has a ground lifter on its ac plug and the other doesnt. If a fault occurs in the lifted device, the fault current flows through the signal cable to get to the grounded device. Its very likely that the cable will melt and burn! Defeating safety grounding is both dangerous and illegal - it also makes you legally liable!I would add a couple of additional points. If the interconnect is single-ended, the shield or other return conductor of the cable will interconnect the circuit grounds of the two components. In many and I believe most designs circuit ground and chassis ground/AC safety ground are not connected directly together. Instead they are often connected together through a low value resistor (e.g., 10 ohms), or in some cases through a much higher impedance, or even not at all. Therefore if an insulation fault causes 120 volts or some other high voltage to be shorted to chassis, in any of those three cases not enough current may flow through the cable's shield or other return conductor to trip the breaker, even if a path to AC safety ground exists via the other connected component.
In the case of a balanced interconnection, depending on the design of the specific components the cable shield may be connected to chassis, but in many designs it will (incorrectly) be connected to circuit ground instead.
Geoff, re your question, see page 8 of the reference I linked to above. And note this statement: "If multiple ground rods are used, Code requires that they all MUST be bonded to the main utility power grounding electrode." Otherwise, as explained in the paper, safety hazards may arise from both equipment faults and lightning strikes. Also note the statement on page 3 that some engineers (incorrectly) "think that system noise can be improved experimentally by simply finding a better or quieter ground. Many indulge in wishful thinking that noise currents can somehow be skillfully directed to an earth ground, where they will disappear forever!" The quality of the earth ground of the AC distribution system is unrelated to grounding issues that may arise within the system, that may affect sonics.
Regards,
-- Al