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Old 3rd May 2009, 02:54 PM   #1
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Default The grounding

I have read Pass's article on grounding many times and I do not have an advanced understanding of electronics only a basic knowledge, but I am still not clear about the notion of grounding.
It appears to be a very complicated topic as was once said to me by an audio designer.

Right. I'm going to state my current understanding and start to ask questions about things I'm not clear about.

1) In an electric circuit, we can have plus, minus or a centre tapped zero point and a plus and minus. This is so that current can flow from plus to minus. However, often, the minus is also shown as ground on the circuit diagram. What does that mean?

2) I have never understood how a ground loop works despite reading up on it dozens of times. My understanding is that a ground loop is nothing but a differential in potential which causes current to flow. Where and how does this potential difference arise?
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Old 3rd May 2009, 05:12 PM   #2
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1) Not much. It's just terminology.

2) This is the much more interesting question. Most of the answer lies in the fact that no conductor has zero resistance. Any current flowing will produce a voltage across the conductor. From that you can see that if you call a certain point "ground" and declare that it has a potential of 0.000000000 volts, no other so-called ground will be at the same voltage (zero) if any current is flowing. In general, you want to arrange ground paths such that the inevitable voltages that are generated across the conductors don't affect other parts of the circuit. This is the logic behind the "single point ground", where separate conductors take the currents back to the defined ground point. SGP doesn't solve all problems though.

Currents flow because a potential has been applied to the circuit, but once you're looking at the details of a circuit, it's more useful to look at it the other way 'round. Current *is* flowing, and conductors have resistance, so what potential differences are generated locally?

I don't find the term "ground loop" all that enlightening as I think it means different things to different people. I just go back to the above application of Ohm's law, and try to think about what happens not only at DC and low frequencies, but at HF as well.
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Old 3rd May 2009, 05:53 PM   #3
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2) I'm not sure I follow what youre saying. I agree that any conductor will have a small resistance. But if we pick 2 points on that conductor why should they be at different potentials?

Two other questions also:

3) In that article by Pass, it states to keep all the length of wires to the single ground point of equal length. But how would this be possible given that the wires all originate from various parts in the circuit? For example one wire might be from the power transformer in which case the wire is as long as the coil. Another wire might originate from the negative rail of the speaker output (say on an amplifier) in which case again, the length is arguably the length of the loudspeaker cable and even the coil and so on.

4.) The article also states that we should not swap neutral and live since the fuse would then also be swapped. My understanding is that the mains supply is to all intents a symmetrical supply, roughly that of a sin wave which we know is periodic and so should not make any difference which way we plug it in?
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Old 3rd May 2009, 06:30 PM   #4
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Hi Conrad and Professor,
My 2 cents, most everybody uses the term ground incorrectly, and that does cause confusion for many DIYers, I believe. To really get a firm grasp you must go back to the way the utility power grid is set up.
Entering your house are 2 hot wires, a neutral, and a ground. In your electrical panel the neutral and ground are tied together, but this still does not make the neutral a ground point. That is why you still have 3 prong outlets throughout your house. The neutral carries the return current back to your power source, just as the DC PS common, or center tap, or minus point in a single supply, carries the return current back to the power supply.
When a lot of diyers lay out their chassis wiring they confuse the roles that parts of their wiring scheme must play. For instance, in a power amp chassis you would not want the return path from the output circuitry sharing the return path from the front end circuitry unless that is inherent in the circuit design for various reasons.
When I lay out a scheme I ignore any thought of grounding anything, I work at returning the circuitry to the PS in as direct a way as possible. The barrel of an RCA connecter is not a ground unless you choose to make it so, it is a signal return path that should be run to the appropriate point in the signal circuitry, not grounded to the chassis, which plays no part in the circuit operation.
I think if we choose to continue to call these points grounds then we should separate them by calling them PS grounds, signal grounds, and chassis grounds, because they are all different.
Enough ranting from me, I know I'll get arguments from someone, but my approach has worked for me for many years.:grin:

Bill
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Old 3rd May 2009, 06:42 PM   #5
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by Professor smith
4.) The article also states that we should not swap neutral and live since the fuse would then also be swapped. My understanding is that the mains supply is to all intents a symmetrical supply, roughly that of a sin wave which we know is periodic and so should not make any difference which way we plug it in?
you live in the UK.
You must have grown up and survived by knowing one must never swap Live and Neutral. We even have polarised socket outlets and polarised plug tops to ensure we cannot insert the plug top inverted.
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Old 3rd May 2009, 06:47 PM   #6
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by Bill Fuss
most everybody uses the term ground incorrectly, and that does cause confusion for many DIYers, ...............
The barrel of an RCA connecter is not a ground ............. it is a signal return path that should be run to the appropriate point in the signal circuitry, ....................
we should separate them by calling them PS grounds, signal grounds, and chassis grounds, because they are all different.
I agree completely, each return should be associated with it's source/flow.
We should start the change here by always being unambiguous when calling up a specific return by it's proper and definitive name.

eg.
Safety Earth is not a ground.
Mains Neutral is not a ground.
Chassis is not a ground.
Be specific, always.
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Old 3rd May 2009, 10:14 PM   #7
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anybody else willing to respond?
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Old 3rd May 2009, 10:24 PM   #8
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Quote:
Originally posted by Professor smith
anybody else willing to respond?

If you ask new questions, then sure yes, but your initial questions has been answered, no?



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Old 3rd May 2009, 10:36 PM   #9
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well no actually people come in here and divert attention.
I dont mind that but it is my topic and I do want my questions to be asnwered. The other thing which I commented on previosuly is that if I ask a question, someone responds then I ask another and somebody else responds. This can be very confusing for me because I cant have more than 1 conversation at once.


So let me post up what i said again:

2) I'm not sure I follow what youre saying. I agree that any conductor will have a small resistance. But if we pick 2 points on that conductor why should they be at different potentials?

Two other questions also:

3) In that article by Pass, it states to keep all the length of wires to the single ground point of equal length. But how would this be possible given that the wires all originate from various parts in the circuit? For example one wire might be from the power transformer in which case the wire is as long as the coil. Another wire might originate from the negative rail of the speaker output (say on an amplifier) in which case again, the length is arguably the length of the loudspeaker cable and even the coil and so on.

4.) The article also states that we should not swap neutral and live since the fuse would then also be swapped. My understanding is that the mains supply is to all intents a symmetrical supply, roughly that of a sin wave which we know is periodic and so should not make any difference which way we plug it in?
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Old 3rd May 2009, 10:53 PM   #10
AndrewT is online now AndrewT  Scotland
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2.) has already been answered.
3.) seems to have been answered by yourself.
4.) has already been answered.
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