Now the Bump in the rug I mentioned earlier
All components should have two separate and Isolated ground planes from each other
One is the Third wire safety circuit which provide a low impedance path way to the ground rod in the event of a fault or short circuit until the breaker can trip ... this circuit is completely separate from the audio signal circuit and only provide a safe path in the event of a fault or short circuit ... there is no audio signal content on the Third wire safety circuit nor should there be ... it's a safety circuit not and audio circuit
07-02-15: Davehrab
Dave,
The ground rod and Mother Earth has nothing to do with the circuit of a ground fault event on the safety equipment grounding conductor.
There are three components of a 120Vac branch circuit.
*The Hot ungrounded conductor.
*The Neutral, The Grounded Conductor.
*The Equipment Grounding Conductor, often referred to as the safety equipment ground or grounding conductor.
The typical residential single phase 120/240 volt electrical panel found in our homes has 3 service entrance conductors that are supplied by the Utility Power Company's transformer.
Two Hot 240Vac single phase ungrounded Conductors and one neutral conductor, that is a center tap connection on the secondary 240V single phase winding of the power transformer. The Utility Power Company usually connects the secondary winding low voltage neutral conductor to the primary high voltage neutral conductor and connects them to Mother Earth.
Why? Mainly for lightning protection. And it is also to help limit the high voltage from crossing over to the secondary output of the transformer in the event of a high voltage to secondary fault.
The low voltage service neutral conductor will be connected to Mother Earth again at the main service equipment disconnecting means. Translation the main electrical service equipment enclosure that houses the main breaker/s.
To keep it simple let's use an electrical panel for the house that has the service main disconnect breaker.
So after the Power Company's meter the 3 service entrance conductors enter the main electrical panel. The 2 Hot ungrounded conductors connect to the line side of the Main 2 pole breaker.
The Neutral conductor connects to the neutral/ground bar.
Per NEC code as well as State and local electrical codes, The neutral Conductor must be connected to Mother Earth again.
Why? Lightning protection and to limit any high voltage that may enter the service conductors from the high voltage feeding the power transformer in the event of a fault condition. (Remember the utility high voltage neutral conductor is connected to the low voltage neutral conductor and then connected to mother earth.)
Finally we are getting to the heart of the relationship of the neutral, (The Grounded Conductor), and the Equipment Ground, (The Grounding Conductor).
So the service entrance neutral is connected to earth using wiring methods and materials that meet NEC as well as AHJ, (Authority Having Jurisdiction), local governing codes in your area. The service neutral must also be bonded, connected, to the metal enclosure of the electrical panel either by a green bonding screw through a hole in the neutral/ground bar to the metal enclosure or a supplied bonding strap that will connect the neutral/ground bar to the enclosure.
We now have created a grounded AC power system with ONE electrical ground plane for the dwelling unit structure, the house.
If we measure from Hot L1, leg, to Hot L2, leg we will measure 240Vac nominal.
From L1 to neutral 120V nominal.
From L2 to neutral 120V nominal.
Note at the main electrical panel the neutral conductor bar and equipment ground bar are one in the same. This is the only place that branch circuit neutral conductors and equipment grounding conductors are connected together. They cannot electrically be connected together at any point thereafter.
Next, finally, lets look at a piece of audio equipment that uses the safety equipment grounding conductor.
If we measure the voltage at the wall receptacle we will find,
120V nominal from the HOT, (small slot hole contact) to the neutral, (larger slot or 'T' hole contact).
From the HOT contact to the U shaped equipment ground contact 120V nominal.
And from the neutral contact to the equipment grounding contact zero volts.
Remember the equipment grounding conductor is connected to the service neutral conductor in the main electrical panel.
So let's create a ground fault event inside a power amp that uses the safety equipment ground. For an example the hot conductor after the safety fuse was installed laying against a sharp corner edge of the iron core of the large EI power transformer. With passing time the heat and 60Hz vibration of the transformer wore an ever so small hole in the insulation just barely exposing the hot wire of the insulated conductor.
Houston we have lift off! If the equipment ground was not defeated and enough current is traveling now on the chassis of the amp to the equipment grounding conductor the safety fuse inside the amp will blow when the ampere rating of the fuse is exceeded breaking the HOT conductor to equipment grounding conductor ground fault completed circuit.
Mother Earth has nothing to do with it. She is not involved in any way. Now of course if you are standing outside in your bare feet on wet grass and come in contact with a hot wire, Ya, then she is involved!
It also should be said Mother Earth does not possess some magical mystical power that sucks nasties from our audio equipment.
Henry W. Ott , Grounding Myths
As for the OP's question about the ground boxes I do not have any experiences with them one way or the other.
With that said I can only add our 120V grounded power system is asymmetrical. We have a Hot conductor that is 120V potential nominal above ground and a neutral conductor that is at zero volt potential with respect to ground.
Food for thought. What is the reference ground plane for a Stealth B1 Bomber's electrical system? Not Mother Earth...
.
Jim