You are absolutely correct and am aware of that fact. Thank you for pointing out that it is against code as I was unaware but it does make sense for safety.
You are welcome. I have lost friends and neighbors through bad safety grounds so am somewhat sensitive to it being corrupted.
Your electrical panel will constantly have imbalances and diligent electricians try to balance loads as much as possible. Imbalances in current from one phase to the other is directed via the neutral bus in the panel to the ground bus with a heavy copper cable to the ground rod or watermain connection in some cases. - the ground rod being close to the panel in almost all cases. Imbalances via the neutral will always take the shortest path to ground.
Technically current will normally take the lowest impedance path, which is not always the shortest path. It depends upon wire size and such, and for ground rods depends upon how conductive the soil and path to the power-line (service) ground. It can get tricky. Water pipe connections always used to be a "go to" solution but that is by no means guaranteed, and often enough these days there is plastic piping so even that does not work.
If the stereo equipment is located considerably further away as it would in most cases, the neutral to the stereo unit should not experience any of this current, and the small few amps required by the equipment ... ie; perhaps about 5 amps collectively,, this imbalance is negligible in so far as the panel is concerned. None the less, what you saying - that the neutral to your stereo unit might act as the house ground if there was a fault in the house grounding and could potentially start a fire or seriously damage your equipment is true and thus the code restriction. The chances are slim but I personally have seen something similar actually happen. Thank you for your input.
The problem arises when something goes wrong and the neutral isolation fails so the stereo (or any other) component chassis can rise to full mains voltage. That's what the safety ground is there to prevent. Double-isolation should prevent that from ever happening, but plenty of us can attest to a failure that led to voltage where it should not be. While voltage is often discussed, as it is easily measured and can indicate a problem, current flow is generally what kills. Static shock happens with a few kV but at such low current that we are not usually harmed (unless we jump and bump into something). However, the current level that can cause pain or death is small, see the old table below (I think is still valid).
I suspect the only way to alleviate this possibility is to put a small amperage inline fuse on the stereo circuit ground wire.
Also illegal (against code), since the safety ground is the "last resort" to prevent shock, and should never be fused.
Ground loops can be insidious but are usually very solvable with some effort to locate and fix the cause. It was popular for a while to implement a "star ground" by bringing the safety ground to a big connector (something like a small battery post or a terminal strip with several screws or lugs for wires) and running a ground wire from every component chassis to that ground point. These days the loop is often from something like the cable line (which usually has a separate ground) or subwoofers (or other amplifiers) plugged into an outlet away from the main system. There are commercial ground isolators for the signal path or wall power to break such loops.
Thank you for your input.
NP. One other thing to note, since I have read now and then of audiophiles implementing isolated ground systems in the interest of reducing "noise", is that if the ground system fails and causes a fire, insurance will normally deny the claim if it was installed in a manner that violates local codes. It is usually up to the homeowner to have any such work inspected to ensure compliance, and get it in writing!
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