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Last Post:
Nov 4, 2009 6:55 PM
Last Post By: Guru of Grounding
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Comments for: "Getting ungrounded"
Posted:
Oct 28, 2009 11:53 AM
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Read the article here: Getting ungrounded |
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Posts:
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12/10/07
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Re: Comments for: "Getting ungrounded"
Posted:
Oct 28, 2009 11:53 AM
in response to: Haldor
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"An ungrounded appliance, for example, can be lethal if its metal enclose accidently connects to the AC mains; a grounded one will pop the local circuit breaker."
The earth ground connection has nothing to do with electrical safety. What keeps metal enclosures safe is the third wire (green) is bonded to the return in the circuit breaker box. This way if a wiring malfunction connects the hot to the enclosure there is a return path to trip the breaker. The only reason why we connect the safety "ground" wire to earth ground is to attempt to reduce touch voltage on the outsides of metal enclosures. This often doesn't work because the local earth ground potential where you are standing may be very different from the earth ground potential at the circuit breaker box.
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12/12/07
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Re: Comments for: "Getting ungrounded"
Posted:
Oct 30, 2009 1:45 PM
in response to: Haldor
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The term "ground" is used as generically for 0V, common, earth ground, etc, as frequently as "coke" is used for Pepsi Cola or Coca Cola.
To the average industry insider, the term can be intuitively interpreted to orient the listener to the talker's frame of reference. To the outsider, the first thing they are going to say is 'Speak English' (or whatever your native tongue is) since they have no background to draw on to understand the speaker's frame of reference.
I have noted in engineering circles that the only time specific grounds (digital ground, analog ground, earth ground, safety ground, ground plane, ground window, ground loop, etc.) are mentioned is when one has to differentiate between the different types of grounds used in a design. For instance, I know that the 'ground window' is supposed to be the common point all other types of grounds are referenced to without 'ground loops', and it is ultimately tied to 'earth ground' somewhere.
Amoungst our fellow engineers I doubt if we will ever become 'ungrounded'.
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Registered:
04/29/08
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Re: Comments for: "Getting ungrounded"
Posted:
Nov 4, 2009 6:55 PM
in response to: Haldor
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Thanks Haldor for jumping on that dangerous but all-too-common conceptual error! This "electron sump" view of dirt, especially for magically draining away system noise currents, is extremely pervasive amongst engineers who should know better. In the professional audio world, where I lecture on the subject, safety ground is often seen as a dispensable "annoyance" and many think that 3-to-2 prong adapters are made for the purpose of defeating safety ground!! Earth ground isn't even necessary for ESD protection unless the structure your body is in (and has its capacitance to) is connected to earth. Is an earth connection necessary to provide ESD protection in an airplane? Remember where the charge is and where the current will flow when a circuit is completed ... current ALWAYS flows back to the source of EMF that drove it - and that may or may not be connected to dirt. Another rampant myth is that all earth grounds are at the same potential. Not so, the dirt carries lots of currents from utility poles, buried pipes, etc. and acts as a big 3-dimensional voltage divider for these currents. Lightning protection is usually the dominant reason for earth grounding ("earthing" for Europeans).
Bill Whitlock, president & chief engineer, Jensen Transformers, Inc., Audio Engineering Society Life Fellow & IEEE Life Senior member
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