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In Reply to: RE: Optimal Grounding? posted by Winston Smith on January 04, 2008 at 14:43:36
Despite the lack of hum, this grounding set-up sounds MUCH dirtier and makes getting a reading of the AC voltage on the chassis' of various pieces of gear I have for proper plug polarity basically impossible, for some weird reason.
When taking a chassis to ground reading you are measuring the leakage of the primary winding of the power transformer of the piece of audio equipment you are testing to the "Grounded Conductor", the neutral. Everybody says ground or earth ground, but the reference is actually the neut...., "The Grounded Conductor". Has nothing to do with mother earth.
The electrical power system of your home is called an AC grounded power system. What that means is one of the three current carrying conductors that enters your home from the utility company's transformer is intentionally connected to earth. The secondary winding of the utility transformer is center tapped and this center tap in called the neutral and will be the conductor that will be connected to earth at your main service. By the way in all most all cases in the US the neutral at the utility transformer is also connected to earth as well as being connected to the neutral of the high voltage neutral feeding the primary of transformer. Thus both primary and secondary neutrals are connected, bonded, to earth at the transformer.
Back at the house....
NEC requires a minimum of two earth grounds for your service. If you have a metallic water line that enters you home that shall be one of them. The other one, 2 ground rods driven outside connected together by one continuous wire that connects back at your house's main service neutral. So the neutral is connected, bonded, to earth ground at two locations, minimum.....
The safety equipment ground.
Per NEC all branch circuit equipment grounding conductors must run back to the panel the branch circuit is fed from. In your case if the panel is your main service panel the ground wire will terminate on the same bar as the service entrance neutral conductor and branch circuit neutral conductors . In some cases extra ground bars are added to the panel and the ground wires connect to these bars. In this case bonding jumpers connect from the neutral/ground bar to the added ground bars.
So as you can see at the main service panel the equipment grounding conductors connect, share, the same termination bar as the main service neutral as well as the branch circuit neutrals. By the way this is the only place that the equipment grounding conductors can be connected to the neutral conductors.
So why do the equipment grounding conductors tie back to the neutral/ground bar?
Lets take a piece of equipment that uses a safety equipment ground. If everything is OK with the equipment no current will ever travel through the equipment ground wire. But if for any reason there becomes a problem with the AC power with-in the enclosure of the equipment and a fault is created between the hot conductor and the enclosure the ground fault current will travel out the safety ground wire of the power cord through the ground pin of the plug through the U slot hole contact of the receptacle and on out through the equipment grounding conductor to the neutral/ground bar of the electrical panel. This ground fault current becomes part of the circuit being fed from the branch circuit breaker in your panel. If the ground fault current is low, plus the load current of the equipment is below the breaker handle rating, the breaker will not trip open. The current traveling in the equipment ground ends up back at the utility transformer and is dissipated in the form of heat.
If the ground fault is severe enough the current flowing in the ground fault circuit will cause an over load and the branch circuit breaker will trip open. Current flow is stopped.....
The lack of a reading on my RadioShack DMM when checking for AC voltage on the chassis' of my equipment is really throwing me for a loop, especially when such readings were easy and obvious previously, i.e., in my old set-up where I used the copper grounding rod system.
First as per NEC the resistance measured at the end of a branch circuit measured from the equipment grounding conductor to the neutral conductor measured at an outlet shall not exceed one ohm......
As I explained above how a safety equipment ground works, how would it work with your isolated ground rod? Follow the ground fault current path. Getting out to the rod is easy but how does it get back to the source? Multiple paths..... Current will always take the least resistive path back to the source. The least resistive path maybe back into your home through one of your service earth grounds. The least resistive path maybe through your neighbors earth ground to his service panel and then back to the source. All the current wants to do is get back to the source, the utility transformer.
NEC says the earth shall not be used as a ground fault current path.
The earth is not that good of a conductor. Depending on the soil and moisture the resistance will vary. In the event of a severe ground fault the voltage drop across the earth resistance could be large enough that the ground fault current will be limited and the branch circuit breaker will not overload and never trip open. Oh by the way in this instance it works great for hunting fish worms......
At your old audio equipment location would you check the resistance from your ground rod #10 wire to the neutral contact of the wall receptacle your equipment was plugged into. Also set the meter to AC volts as well as AC millivolts and check for voltage from the #10 wire to the neutral.
As for not getting a reading at the new location for a proper AC polarity test, it may be the meter.
As for more noise you are now hearing where you now have your audio system many factors may come into play. I will only address the AC aspects.
The branch circuit, the system is now plugged into, is sharing other receptacles with loads causing EMI/RFI.
The branch circuit could be longer than the one at the old location. It could be picking up EMI/RFI noise.
The branch circuit could have a corroded connection/s somewhere between the breaker and the receptacle the equipment is plugged into.
The contact pressure of the receptacle is poor. This will definitely cause noise.
The breaker that feeds the new location could cause the problem due to its location in the panel.
The breaker could have poor contact pressure to the panel connecting buss tie.
Note not one equipment ground related issue in my short list.
Follow Ups:
Dear jea48;
WOW! What a treat! Thanks a million for the fabulous information. Ultimately, your conclusion is that grounds are rarely (if ever) at fault for sonic dirtiness, as opposed to hum-loops. Agreed. But the strange behavior of the DMM is still perplexing, as I did check its performance and it is working properly. Maybe there's simply no voltage leakage, or so little my DMM can't pick it up, even at the 300mV range (the most sensitive setting, I believe.) No biggee, though. I'll just use the CDP's stock plug with its mandatory polarity, which I'm sure will be just fine. If I get a wild hair in the wrong place, I can always cheater plug it and invert and listen, going back and forth, although I prefer the ease and certainty of a DMM reading, if possible.
Also, I'll have to check the main service box for appropriate wiring, as per your descriptions. I already found one wall outlet that is wired with no third pin (ground) connection AND polarity inverted, and many others with no third pin (ground) connection. So much for build quality and integrity of my home's electrical system! Geeeeeeeez Louise!
As for my query on checking ground lines for relative effectiveness and functionality, thanks for the NEC standard and all the other info. I'll take my trusty DMM out and check to see resistance at each outlet's neutral pin, as per your instructions. My real concern here was echoed by your analysis as to the 'dirtiness' problem, that is, that there may be an interior connection or wire that is corroded or loose or otherwise problematic, and thus may limit the effectiveness of that circuit to function cleanly and with low distortion. I hope the DMM's Ohm reading sensitivity will be sufficient to determine if any outlets (or the precedent wires/connections therein) are substantially inferior to the other outlets (although your analysis seems to conclude that such concern is completely misplaced.) I suspect you are probably right, but I'll play around anyway, and see what happens. (Very little, most likely.)
But again, I just want to close with another 'thank you' for the super effort you put out to help me in my search for answers. It is VERY, VERY MUCH APPRECIATED!!! THANKS SO MUCH!!
HAPPY NEW YEAR AND HAPPY LISTENING!!
Everything jea48 says is correct, but that does not mean the AC safety-earth wiring is not to blame for lots of audio problems.
The wires are meant to carry fault current at 60 Hz, but by how they are configured, they support radio-frequency noise. The connection to earth is a long way away for RF noise.
You could have a problem if your new circuit's safety-earth is picking up noise from a non-audio appliance. The best way to find out is to go around and unplug every possible noise source, one at a time, and listen for an improvement. Unfortunately, almost every appliance made these days has a computer inside, and a switching power supply to run it, and these things are always on as long as the appliance is plugged in.
Dear Al and others:
Geez, am I a jerk or what? I never thanked you, Al, and all the others for your assistance on my question, and just today realized it when I re-read this thread (I read inmate responses over and over until they eventually lodge in my tiny brain.)
Please accept my very belated thanks for your kind and informative assistance here, and to all who contributed to this thread. Your help is GREATLY appreciated. (And again, a special thanks to jea48!)
Sorry I forgot my manners. My mama raised me better than that!
Winston
The connection to earth is a long way away for RF noise.
Hi Al. A while back Steve Eddy challenged me to produce any reliable evidence that RF noise can be bled, drained, off to earth ground. I spent a few hours, off and on, on Google trying to find any credible evidence. Do you have any? I even talked to a Ham Radio operator about it.
Just for the heck of it I tried an experiment with 2 well powered walkie-talkies. I took one of the radios and grounded the antenna to a good earth ground. The grounding of the antenna had absolutely no effect on the performance of the radios.
As you know a Faraday cage does not need to be grounded to reject RFI. Don't most CD & DVD players have doubled insulated power wiring, and do not use an equipment ground connection?
Your thoughts appreciated.......
We both know the purpose of the safety-earth wiring, so I won't go into that again.
At 60 Hz, the wire lengths in typical houses are short compaed to the wavelength and there is no transmission line behavior to worry about.
However, at 100 MHz, the wires are long. They behave as poor transmission lines and the RF noise propagates along them. Some of the noise may be absorbed by the earth connection, but most of it is simply reflected at impedance changes. These are the points where the wiring goes through connections or past surrounding metal objects, etc.
A radio antenna may require an earth connection to function properly, but that is because the antenna is physically located at the connection, and is using the earth as a mirror. The long safety-earth wiring in a house would not be suitable for that kind of RF grounding, as you found with your experiment.
Most audio systems have ground loops, as more than one component uses the AC safety-earth. Even if there is no 60 Hz hum from the ground loop, the RF noise present on the AC safety-earth wiring gets into the ground loop and degrades the audio signal. This is why many components are double-insulated: they do not make the safety-earth connection and avoid the ground loop altogether. They are not built as Faraday cages, however, and are just as susceptible to broadcast RF noise as three-wire equipment.
> > They are not built as Faraday cages, however, and are just as susceptible to broadcast RF noise as three-wire equipment. < <
> > > > > > > > > > > > > >I was under the impression that is exactly what the metal enclosure around a CD and DVD player is. I would agree RFI can enter through the power cord. It also can go back out from the equipment back on the power cord and end up on the AC power line..
===============> > The long safety-earth wiring in a house would not be suitable for that kind of RF grounding, as you found with your experiment. < <
I preformed the experiment on a job site. The ground was the central grounding grid point in a large mechanical/electrical room. The earth ground was more than antiquate. I thought for sure when I grounded the antenna the radio would not transmit or receive. But as I said earlier it did not effect the radio one bit.
One thing I remember the Ham operator said about the earth absorbing RFI, he said if that was the case the transmission of radio waves wouldn't work. Especially AM.
Jim
==================
There are various holes for the CD drawer, the display, ventilation, and the mating edges of the case pieces are not designed to maintain conduction. In addition, the power cord inlet and the audio output jacks may allow noise to get in and out.
See the link.
But the strange behavior of the DMM is still perplexing, as I did check its performance and it is working properly.
Test was flawed....... Good chance there is a difference of potential, voltage, between your isolated dedicated ground rod and that of your homes "Grounded Conductor", the neutral. Maybe small but still in series with your meter and the equipment you were testing.
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