Popular Post JohnSwenson Posted August 22, 2020 Popular Post Share Posted August 22, 2020 OK since my name was mentioned, back into the fray again. First off there are several things called "ground' they are not all exactly the same thing, although somewhat inter-related. 1: AC mains side 2: signal side #1 is all the 50/60HZ "wall socket" stuff #2 is signal interconnects such a RCA audio cables, XLR interconnects, USB cables, Ethernet cables etc. AC stuff There are two primary grounds here: Safety ground, otherwise known as the "third pin". I'm not an expert in other countries, but in the US this is a wire that is bonded to the neutral wire in the main electrical panel. This is supposed to be connected in the "components" to the outer case, its purpose is to trip the breaker in the electrical panel when a short occurs between the hot wire and case. This prevents YOU from making the connection to neutral. This circuit has to have a low enough resistance that enough current will flow to trip the breaker. "Earthing", this is a connection to a ground rod or metal water pipe in the ground. Its other side is the neutral in the electrical panel. Its purpose is to keep the overall voltage of the AC system in your house from getting too far away from anything that IS connected into the ground (such as water pipes, steal beams into the ground etc). Remember that the AC wiring in your house is connected to the secondary of a transformer (on the pole or underground), such a floating system can theoretically float hundreds of volts relative to ground. The earthing connection prevents that from happening. Earthing is not some magical thing. The connection is usually fairly high impedance, cannot support much current (unless you really work hard at it). It does not automatically "suck up" noise. This connection actually has little to do with noise etc. (except making it worse in some cases) The safety ground is usually just a simple 12 AWG wire that wanders around from the electrical panel to your outlets. It may go through splices and connections before it gets to any particular outlet. There CAN (and almost always WILL be) voltages between the safety ground pin (third pin) of one socket and another. Most of this comes from magnetic coupling from the neutral and hot wire and safety ground wire. You would think that the fields from the hot and neutral would cancel each other out, but this would take a completely symmetrical geometry of the cable, this very rarely happens. This voltage between third pins can easily create 50/60Hz noise between components, commonly called "ground loops" . This post is not about how to fix such things, that is MUCH bigger than one post! #2 is the "signal interconnects" These may or may not be connected to a safety ground connection. Various interconnects connect "signal ground" of different boxes. Noise can move from box to box over the signal grounds of boxes. So how does 50/60Hz from #1 get to #2? There are two primary methods: ground loops: mentioned above, the voltage difference between safety ground pins on different sockets. leakage currents: These are small AC line frequency currents that go between the the AC line and the outputs of power supplies. Leakage currents form loops either from PS outputs to a safety ground and then back to the neutral OR through another power supply. SMPS supplies have made this much worse than it was in the days of "transformer" supplies. Again how to fix this is WAY to big for this post. So how do these "grounding boxes" fit into this? They have a wire going from a box into either a #1 or #2 ground. So what do they do? It has absolutely NO connection with ground AT ALL. They ARE in fact antennas as has been mentioned. BUT in some circumstances that CAN actually lower 50/60Hz noise in a system. Huh, how can that work? Remember that given a particular AC signal if it is added to another signal of the same frequency but opposite phase it cancels. What happens with these boxes is that most of what the antenna is picking up is the line frequency (50/60Hz), all that RF stuff is much lower in amplitude. IF you somehow get the phase of the signal coming out of the box to be opposite to the phase of the existing 50/60Hz in your ground system (from ground loops or leakage current) it will, at least to some degree, cancel out that existing noise. My guess is that these "ground boxes" are antennas with phase shift networks of some sort. My personal opinion is that this is the wrong way to be going about fixing "grounding issues". If you change anything in the system then the carefully concocted "noise injection" will be different and it may wind up INCREASING the noise rather than helping. I personally prefer getting at the root of the problem and fixing ground loops and leakage issues directly rather than using carefully crafted band-aids. Please note I did NOT say they can't work! Just that I don't think they are a good way to deal with the issues. John S. zerung, Speedskater, sandyk and 7 others 4 6 Link to comment
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