Stuart Polansky wrote:
Re: isolated ground. What you wrote is true, Paul. The confusion lies in that an "isolated ground" receptacle has an insulated green ground wire running from the U-ground receptacle contacts to the main bonding jumper (in the panel). This grounding conductor is "isolated" from the "safety ground" that is the outer sheath of an armored cable, the bare conductor of NM (Romex), or the conduit enclosing the circuit conductors. That "safety ground" wire connects all of the metallic elements of the wiring system to ground potential. In a normal receptacle, it also connects to the u-ground contact.
The purpose of the isolated ground is to isolate the load (data processing usually) from noise generated by other equipment on the circuit, or connected to the grounding system downstream of the main bonding jumper while still providing the drain & safety connection to the isolated ground load.
The thought here being that the main bonding jumper is a low impedance connection to "ground" and that noise should be virtually non-existent at this point, because it is shunted to ground. Reality is a bit different, as we are all aware.
The better solution IMHO is to use an electrostatically shielded 240V input, 120V output transformer on a dedicated circuit (more than one if you are like Tom P. with thousands of watts of amplification), then connect the grounded conductor of the secondary to the household ground, whether it be cold water, building steel of (in a newer home) the Ufer (foundation) ground. In the last scenario, overcurrent protection on the secondary is a must. In a high wattage situation, a 30 ampere 2-pole breaker from the house CBP could supply a 5kVA 240/120 transformer. The secondary of that transformer could deliver ~40 amperes @ 120 volts, so one could use 2 or more separate circuits to feed amp(s) on one circuit, preamps, tuners, DACs, turntables, etc. on another. ANY high wattage device (like a 2000 watt amp) should be on its own circuit to avoid causing voltage fluctuations in the circuit feeding the other gear (a HUGE, oversized, transformer helps here as well).
Is that confusing enough? LOL, it's clear to me since I kinda live this stuff, but if anyone is interested, I'd be happy to chat and help out.
Stuart
Actually, as far as capacity, I run my whole system with all amps and other equipment on one shared 15 amp branch circuit. I want only one line to minimize ground loops. With the dynamic range of music plus the large internal storage capacity of the power supplies in all the equipment, I have never tripped a breaker. The internal storage flattens out the spikes in the input current requirements on the mains. However with all that equipment, if I did not have a soft start circuit I would probably pull the distribution box off the wall when I turned the system on.