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In Reply to: Oh yeah? posted by Triode_Kingdom on April 26, 2007 at 21:16:56:
Hi.Earth grounding is important for:
(1) it ensures personal safety (DC grounding)
(2) it protect equipment involved (DC & AC grounding)
(3) it is necessary to pass the electrical authority approval if appliable; (DC grounding)
(4) it prevents EMI/RFI. (AC grounding)
(5) it provides a known reference to the control signals for control
equipment. (AC/DC grounding)DC grounding to the chassis is imperial in case of HV insulation breakdown in HV carrying devices, e.g. power & O/P transformers, HV chokes etc in audio amps. The split-second shorting DC currents can be drained away via the chassis & the earth ground (green) wire of the 3-wire AC mains supply cord. The earth grounding wires must be thick enough ie. of the min gauge sizes) to conduct away the shorted DC currents.
The contact of the green earth ground wire must be bolted or properly soldered to the chassis to allow zero contact DC resistance.
AC ground is more complicated issue as we are dealing with RF energies which require adequate SURFACE AREA (of the chassis, etc) to drain away of RF currents. The conductors/contacts must have very little inductive & capacitive reactance to ensure lowest impedance to drain away of harmful RF energies.
There is why for digital/RF systems, effective AC grounding a hell of big issue to address.
Follow Ups:
My point is that the application of the term ground is ubiquitus for circut Common. The circut will function (as a circut) without an actual Earth Ground connection, irregardless of the SAFETY or EMI/RFI benefits of likewise sharing a chassis connection to Earth for AC-operated devices. By refering to such circut Common returns as the ground, confusion per wiring schemes can arrise & often does with novices.
and I am seeing some serious misinformation in some other posts.As I see it your main point is that the signal circuit could be entirely floating. Given that the (hot) signal is from the plate of a tube (usually) and that plate voltage is rectified AC with the filter cap's negative side going to normal electrical ground it seems to me signal is already (AC) referenced to ground. Given that the return path for the signal is the tube's cathode and said cathode is referenced to the same ground the filter caps are, which is normal electrical ground, you are still involving electrical ground. Even if you don't have a 3-wire cord the neutral wire is referenced to normal electrical ground and at the least there is a cap between neutral and chassis if the neutral isn't simply bonded to the chassis.
About the only way you are truly getting away from normal electrical ground is if you transformer couple. Even balanced IO's involve electrical ground.
BTW, irregardless isn't a word. American electrical code requires the chassis to ground bonding be done with a minimum of a #8 screw and never soldered. And a separately derived ground via running to a water pipe is highly illegal and potentially very dangerous. Okay, I have had my rant for the day and nothing personal gents :)
"irregardless isn't a word"Oh, how I wish that were true. Unfortunately, it is in my Websters Unabridged as a synonym of regardless...
Well, you are saying that the DC power supply establishes *electrical ground* as a current return pathway for the circut. I am saying that your *electrical ground* is actually the circut Common return path, and that no actual connection to an Earth Ground is required for said circut to function as a circut, therefore why refer to such as a ground vs Common? By refering to such as ground, confusion can arrise & in fact did with the OP. Thanks for the English language lesson, but what does that have to do with the topic under discussion? Unless you were making the same point that correct terms DO matter after all.
I am simply trying to understand you. Good chance we are saying the same thing in different words. The neutral is considered an "earth grounded" current carrying conductor. So we can't get away from the fact that out power transformer primary has a ground connection.I think I must be missing an important point you are making. The only way I see is with balanced inputs and differential amp stages. Even then any unbalanced stuff can have the potential to go to ground.
Of course it goes without saying that the signal from a preamp goes only to the input tube's grid (and not through said tube) and straight to chassis/signal ground by way of grid leak resistor. If one has a 3-wire cord, or a cap from neutral to chassis, then you have signal connected to electrical ground.
If we wish to avoid electrical ground then best we avoid single ended stuff in general. But home audio, as well as 120VAC in the states, are both single ended in nature. Personally I run 60-0-60 balanced power and avoid a neutral. But I still reference signal ground and chassis to electrical/earth ground for safety reasons.
For instance, if your circut (any circut) were battery powered, then there is no actual Earth Ground connection. Yet the circut still operates, because there does exist a Common pathway for current return. With AC Mains powered equipment, the separate power supply circut derives the DC voltage to operate the audio circut, and again except for Safety with such AC Mains powered devices, there is no audio circut requirement for an Earth connection. But refering to the current Common return as an electrical ground DOES sometimes cause confusion as to how & where to make a Safety Earth Ground connection to the circut. Another example is *ground loops*, which are actually current loops that may exist even when no Earth connection is present. I must wonder if anyone bothered to read my original text, or just the subject header. Anyway, guess old habits are hard to discard, especially after a century of use.
Hi.I know where you come from. This is very common sorta misunderstanding btween signal return reference "ground", & actual electrical "earth" ground, or whatever yu can put it.
You're correct for audio amps DC powered, as long as the signal in & return circuit is completed, the amp functions.
But if the amp is working in an EMI/RFI noisy environment, like in many modern homes today, where tons of computers, notebooks, flat panel TVs are all over the place, the poor amp is subject to HF rash.
So metal chassis of the amp still needs to be earth grounded so that the harmful RF energies can be drained away via the earth path as per my post above despite the in/out signal circuit is completed.
As I posted earlier this week, my SS phonostage, a dual-monaural stereo design, full battery powered, still got its plastic housing full laminated with aluminum foil, which is AC grounded to the turntable chassis ground wire as well as the ground rod of the tube phonostage/line amp where the SS phonostage unit hooked up to its "
AUX" input.EACH of the I/P jacks of the SS phonstage unit is AC grounded to the plastic housing aluminum foil shield via a 0.1uF3KV ceramic disc cap,
an excellent potential RF rash short-cut from the amp return reference ground.c-J
bot
Russ> > Even if you don't have a 3-wire cord the neutral wire
> > is referenced to normal electrical groundI have found many houses where the polarity
of some of the outlets were switched so
if you are thinking that the polarity plugs
mean anything you are mistaken.> > a separately derived ground via
> > running to a water pipe is highly illegal
> > and potentially very dangerous.Do you realize that most houses are earth grounded
through the water pipe which goes into the ground.
How is this illegal let alone dangerous?
The pipe which is filled with water is a
better conductor than the house wiring and
it is buried in the ground outside the house.
But I can't abide telling someone to break them in an open public forum.Yes, you are correct that the neutral, ground rods, and utility service pipes (even building steel in some cases) should all be bonded together. But the important point is that they are to be bonded together at one place and with one unbroken wire. Just like in your amp you don't establish one main star ground point and take half your grounds there and just solder the other half to the chassis any old place. That leads to ground hum due to a differnt impedance (or potential) to ground even though the chassis is a large conductor compared to the currents involved.
Now if unknown to you, said water pipe had a high impedance for any number of reasons....like a poor screw/solder joint....or a bit of plastic pipe...or whatever....it could indeed have a high enough impedance to prevent the breaker from tripping. 120volts/20amps=6ohms so if you have anywhere near 6 ohms difference between water pipe and neutral the circuit breaker would not work....plus if someone was in the tub bad news. Also keep in mind that during a true short circuit said breaker will actually develop fault currents near 10,000 amps....and that is no small current. Best to follow code and have all grounds originate and terminate in one location.
RussI could refute each and every one of your statements
but the imformation is out there let people decide.
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