Saki70, as explained by an Audiogon member who is an electrician in another Audiogon thread several years ago (that I can't find now), what the isolated ground does is prevent the ground from being connected to the chassis of the receptacle. With both isolated ground and a non-isolated ground installations, the ground comes back to exactly the same place on the bus bar of the breaker panel. The only difference is in whether the ground is connected to the chassis of the receptacle.
If the receptacle and enclosing outlet box are attached to metal studs in commercial construction, the chassis is now making contact with the metal stud and hence to the rest of the building structure. With the ground being connected to the chassis (not isolated), your ground is now connected to the entire building structure. That can make for all sorts of noise, interference and hum possibilities. So, in commercial construction, you'd absolutely want to isolate the ground from the chassis: i.e., use an isolated ground receptacle and wiring installation.
On the other hand, in wood stud construction, the outlet and chassis are nailed to the non-conductive wood stud. There is nothing from which you need to isolate the ground. It no longer matters that the ground wire is not isolated from the chassis of the receptacle.
There is one other possible factor and that is the possibility of the fourth wire in the isolated ground installation providing some EFI drain or shielding for the length of cable back to the circuit panel. I don't know about that contention. I think you'd be better served by taking the trouble to twist the wires which make up the cable if you're trying to get maximum EFI rejection along the length of the cable.
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If the receptacle and enclosing outlet box are attached to metal studs in commercial construction, the chassis is now making contact with the metal stud and hence to the rest of the building structure. With the ground being connected to the chassis (not isolated), your ground is now connected to the entire building structure. That can make for all sorts of noise, interference and hum possibilities. So, in commercial construction, you'd absolutely want to isolate the ground from the chassis: i.e., use an isolated ground receptacle and wiring installation.
On the other hand, in wood stud construction, the outlet and chassis are nailed to the non-conductive wood stud. There is nothing from which you need to isolate the ground. It no longer matters that the ground wire is not isolated from the chassis of the receptacle.
There is one other possible factor and that is the possibility of the fourth wire in the isolated ground installation providing some EFI drain or shielding for the length of cable back to the circuit panel. I don't know about that contention. I think you'd be better served by taking the trouble to twist the wires which make up the cable if you're trying to get maximum EFI rejection along the length of the cable.
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