I have an A/V receiver that has a two pronged outlet plugged in. I connected a 16 gauge wire from the groundpost on the receiver, to the center screw on the outlet. There is 119V AC between the neutral and hot lines in the outlet, .3V AC between the ground and neutral lines at the outlet. The neutral and ground lines are tied together in my electrical panel. There is an 8 foot copper rod burried in my back yard, with a 4 gauge wire connected between it and my panel. There is also a 6 gauge wire connecting my panel to my cold water pipe. There is really bad white noise unless I disconect the ground wire between the outlet and the receiver. I feel that there should not be a potential between the neutral and ground wires. Any ideas?
If wire were as perfect conductor, then no voltage would exist between ground and neutral. 0.3 volts is not unreasonable. In fact, it suggests almost no current on that circuit's neutral wire.
You are asking an EMI/RFI question that is difficult for EMI professionals even if on site. You must do experiments. Furthermore you must understand the concepts of normal mode and longitudinal mode noise to make your testing more productive.
What is the complete circuit that carries noise into and out of the receiver? This, of course, means you understand ground loops - which is the same reason you had that 0.3 volt difference between neutral and ground.
Welcome to the EMI/RFI world. To get better answers, provide better information on the circuits - everything that connects to receiver, ground etc - and detailed responses to tests. Most who don't learn concepts such as ground loops, above noise modes, etc end up just doing what causes less noise without learning the why.
Your question begs deeply for you to understand the concept called ground loops and why single point grounds are so essential. For example, all equipment connected to that receiver must share a single point ground. Then that single point ground must connect to one wall receptacle safety ground. Your building then connects all receptacle safety grounds to a single point ground in breaker box. Then that breaker box safety ground connects with all other utilities to a single point earth ground.
Notice the trend. Everything adjacent connects to a single point ground. Then all those 'adjacent appliance' groups, in turn, share a single point building ground.
It is possible that other appliances c> I have an A/V receiver that has a two pronged outlet plugged in. I
It almost sounds like you have a bad connection, like maybe the center screw on your outlet. A bad connection could cause the noise you are hearing. By bad connection I mean not a solid connection, if there is paint on the screw you do not have a reliable ground connection.
It is not uncommon to have a voltage between the ground and the neutral. The neutral should be grounded back at the transformer neutral and not in your panel. You may have ground loops which could cause noise. I would check out all your ground connections to ensure they are metal to metal, clean with no dirt or paint or other material that could interfere.
The receiver is almost certainly grounded via the neutral internally. The ground post is most likely intended for connection to a turntable. And BTW, you'll rarely find dead zero polarity from ground to neutral at the device end, especially with power being consumed *anywhere* in the circuit.
you know the ground and nuetral are tied together in the service main. if there is interfearence between the ground and the nustral bfor the main panel then yes it is screwed up somewhere. if the circuit is secure through the house then the power company is to blame. dont tell peopleit is normal to have a difference in [potential between there neutral and there ground in there home because it isnt period.
ok you the third that has said that. maybe i am wrong. if so cool. but how could there be a voltage on the noutal or ground if they are bonded together in the main panel. load or no load the noise depends on a connection doesnt it?? fearfakter
The unit is hopefully NOT grounded via the neutral internally as this wold imply that an incorrectly wired socket would liven the frame of the unit and cause a short circuit or worse.
In theory, with the neutral and ground tied together at the building entry, there will be no voltage between them but that is theory only. The neutral carries the load current and hence there will be some voltage drop across the resistance of the wire. The Ground should not be carrying any current and so the ground at the load end will be the same potential as the tie point at the building entry. This means there will be a small voltage difference between neutral and ground at the load end depending on the size of the load current. This voltage should be very small but measurable. Modern practice requires a ground WIRE back to the entry panel and does not rely on the outlet cover screw which in turn relies on the conduit continuity which is not always as good as expected.
Maybe someone else could tell us what NEC or other authority says is acceptable voltage between neutral and ground at the load..
Its way more complicated than that, but to simplify it way down, think of voltage and current like the chicken and the egg; it doesn't matter which comes first because one can produce the other. The current at other points in the system have a slight effect on the neutral current at any given location. Combine that with the slight resistance of the wire length to the panel bond and VIOLA! you have enough variables to complete ohms law and produce a voltage (also slight) The numbers you posted are nothing to get upset about.
fearfakter's post is correct if wire is a perfect conductor. Wire is not a perfect conductor. Basic electrical knowledge (which also explains ground loops) demonstrates why a 0.3 volt difference between neutral and safety ground (at receptacle) is normal. And that is the point - the numbers. To understand why, one first learns numbers such as current down that neutral wire AND wire resistance. Two wires connected together tell us nothing useful without those numbers.
It is normal to have a difference > ok you the third that has said that. maybe i am wrong.
It is normal. The neutral and ground connect together at the main panel. The neutral carries current from the loads. Therefore, there is a voltage drop from one end to the other. The ground carries no current, so the voltage is the same at both ends. Therefore, anywhere downstream of the panel, the neutral is at slightly higher potential than the ground. It varies depending on loads and location, but could be from millivolts to several volts.
Ohm's law. Because E = IR; the current through a conductor times the resistance (however small) of the conductor equals the voltage drop from one end of the conductor to the other. A current flowing on the neutral will always cause a voltage drop.
To give him an example, suppose there is 30 feet of #12 wire for the neutral to where it is tied to the ground. (A table I have says 1.619 ohms per thousand feet) .04857 ohms. With 6 amperes though the return there would be a .29 volt difference between the return and ground. A connection will usually have an additional drop.
My receiver and computer are on the opposite sides of the room, and do not share the same outlet. That would explain the ground loop. If I was to purchase a new receiver, does it come with a three prong outlet, and if so, would it make sense to get a 25' extension cable so that the computer and receiver are sharing a ground?
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