An Electrical Contractor and Audiophiles' view
I don't often speak up on this forum, but I can shed some light on this subject -both in theory and extensive experience. Sorry to be long-winded, but bear with me.:blah:
My background as an Audiophile since 1978, Electronics hobbyist/fanatic since age 6, Musician since age 8, an installer of Electronic navigation and communication equipment growing up in My families' boat dealership, a Commercial Electrical Contractor since 1990, Live Sound Engineer for the last 7 years, and a custom audio/video/communication/data/surge and noise suppression system installer in custom homes, have taught me quite a few lessons.
First off, regarding the neutral and ground: The ONLY place your neutral and ground should ever be directly connected is at the FIRST POINT OF NEW ELECTRICAL SERVICE. This is defined as the Service Entrance to your power Source, i.e., The first electrical panel after the electric meter or the transformer inside your business or residence that provides power to that panel. After that, neutral and ground never see each other again UNLESS the power is fed through another transformer, where the neutral is bonded to ground to keep the neutral from "floating" away from 0 volts and keeping the power legs at the proper 120 (or 208 or 277) volts with respect to ground and neutral.
That is why your neutral SHOULD read ZERO volts with respect to ground at any point within your electrical system.
The reality is that wire has resistance (albeit small); and wire connections and joints (splices) are the devils' advocate in the form of corrosion and small/weak contact at the connection points. This means that voltage to ground will always be something besides 0volts (neutral) and 120volts (line) when there is current flow feeding a connected load. The bigger the wire and the shorter the length of it, and the cleaner and tighter the connections, the better. Also, the less connections (joints) in the circuit the better. Most electrical problems or failures are a result of failure of the connection or contact point (relays and switches).
I learned this at an early age: try powering everything with 12 volts DC and using it in a boat in salt-water. It takes heavy-gauge wire and clean, corrosion-free connections to get things done in this environment. That, and a lot of maintenance and troubleshooting as time goes by.
It is important to understand that grounding should be done in what is refered to as a "star" pattern: all grounding and grounded (neutral) conductors should come together at ONE POINT ONLY. Anything else constitutes a ground loop condition which, due to the resistance of the wire itself and the different path lengths/resistances, creates either a souce for hum and noise or an antenna to pick it up, inducing noise into the electrical system.
Isolated ground electrical receptacles differ from normal receptacles in only one aspect: the ground pin contact is NOT CONNECTED to the metal mounting straps that secures the receptacle to the box it is mounted to. That's it. As Zilch pointed out, homes are usually wired with romex and boxes are plastic. The frame of the house is wood. No path to ground except through the grounding conductor in the romex, which only sees ground (or neutral) at the aforementioned first point of new electrical service.
In commercial buildings, where the wiring is inside metal boxes connected with metal conduit and usually in a metal-stud wall in a metal frame structure, the "antenna effect" of these multiple ground paths can be a real problem for sensitive electronics dealing in low-level signals that require a lot of amplification. The copper ground wire is considered the only reliable low impedance path to gound, but certainly not the only one. This is particularly important when the power is run undergound in PVC plastic pipe abd pops up into a receptacle box. This is why normal receptacles have a ground connection to the metal mounting strap: the metal box must be grounded in case a short occurs inside the box or pipe, so the box and pipe will short to ground and trip the circuit breaker instead of making everything "hot" -a definite safety hazard!
In commercial electrical installations, a "Clean Power" system has several distinctions:
1: a separately-derived system, either by isolation transformer or dedicated step-down transformer from 480 to 120 volts. These are usually "K factor" transformers, which means oversized windings (for low source impedance, which equates to higher transient current capability for more stable voltage under dynamic load conditions) and extensive electrostatic and electromagnetice shielding for lower noise both airborne AND on the power leads.
2:Separate grounding systems:
1 for the building, conduits, electrical boxes, and the neutral bond
inside the transformer itself.
1 isolated ground system for the ground pins at all of the 120 volt
receptacles feeding the connected equipment. This requires the use of
isolated ground receptacles and isolated ground buss bars inside the breaker panel for the receptacle grounds only, with its' own separate heavy-gauge ground wire connected to the ground rod.
3: Often, the Electrical Engineer will specify a separate ground rod driven
at least 6 feet away from the "Dirty" ground rod used for the transformer, building steel, and the electrical raceways (i.e. transformer case, electric panel, conduits, junction boxes, etc). This utilizes the raceway system as shielding from airbone interference and noise, the "dirty" ground wiring as ground fault protection (safety), and the "clean" ground to serve primarily as a drain for noise generated or picked up by the connected equipment being powered.
There are several sources of noise that can eek into our audio and video systems traveling into or even generated within your home either over the air or on the power lines themselves:
Your neighbors' ham or CB radio (RF interference), noise traveling in on your cable TV feed as well as voltage difference between the cable ground and your electrical system ground, electric motors in or outside of your own electrical system (commutator brush arcing noise) , ignition systems on engines, electrical arcs in switches and contactors as they open or close, Neon, flourescent, or HID lighting, your own audio equipment (digital and analog), microwave ovens, and of course your PC.
What you need from your electrical grounding system is a path to ground for ground faults (electrical shorts); what you want is a low-impedance drain for noise.
What you want from your electrical power circuit is clean 120 volt, 60 Hz sine wave power with no noise on top of it.
The importance of tight connections with no oxidation on the contact surfaces cannot be overstressed. This is where hospital-grade receptacles play a role. Instead of brass contacts with relatively weak contact pressure in the cord socket and the wiring points, Hospital-Grade recepts use heavy spring pressure in the socket spring, and all contact points are plated with chrome or rhodium.
Years ago, I was called out to install a new Electrical Panel and address an interference issue. The customer was a retired Audio and Computer Engineer, and had over $25,000 in Audio/Video equipment. He had just bought the home, and FHA financing required a Main breaker or "other means of Main disconnect" and his panel had no Main CB. The symptoms were hum in the audio, "herringbone" interference waving across the TV screen, and a strange "dancing dots" phenomenon on TV with the computer on in a room on the opposite side of the house.
I traced the problem to the neutral bar in the Breaker panel It measured 8 volts with respect to the ground rod itself. The culprit was corrision and oxidation, especially at the panels' ground wire at ground rod itself. New fresh connections on bright, shiny copper eliminated the video noise, but the hum persisted.
The incoming cable TV shield measured 300 millivolts to ground. New cable ends didn't help much. I tried a trick I had learned: a 75ohm>300ohm "balun" transformer on the cable connection to his TV, and the hum disappeared. This works by isolating the cable ground from the audio/video equipment ground. New cable installed by the company from their distribution box to his house eliminated the problem. The new Electrical panel and the requisite renewing of all the electrical connections within it further improved the sound and picture quality.
Years later, three dedicated 20 amp circuits with oversized (#8AWG) wire from the panel to his living room (only 30 feet of wire) and separate neutrals for each hot were installed and a main surge/noise suppression system installed in the electrical panel yielded great benefits in terms of lowered noise floor, better/more solid imaging, and more dynamic impact on transients. Nothing mysterious to me: just a cleaner more stable power source with better transient current available through the heavier wiring.
When it comes to devices such as this PS Audio item, You are benefitting from the Hospital-grade receptacles, as well as extensive noise filtering of the hot and the neutral conductors to ground. It still depends on good integrity of the Electrical grounding system and low resistance in all of the wiring.
It is possible that under such circumstances as I outlined above, an outboard device such as the PS Audio item may provide little or no improvement. Some of these devices can actually hurt by limiting the maximum transient current flow to your power-hungry amplifiers and voltage-sensitive equipment with meager and/or poorly regulated power supplies.
How about a dedicated ground?
Since most panels will tie in the ground and neutral on a shared bus with the true ground wire (solid copper core) exiting the house and buried deep in the ground (get it? ground?)- I always wondered what (if any) benefit would come from running a TRUE isolated ground line for your dedicated receptacle?
...from the receptacle- run a dedicated copper core wire right through the walls and to the outside on a rod and drive it a good 6' in the dirt.