Re: Powered monitors ground loop


<westom1@xxxxxxxxx> wrote in message
news:726b22f6-4e18-440c-925e-aa8be00daf21@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jan 17, 12:28 pm, makol...@xxxxxxxxx wrote:
If you take a piece of wire, form it into a loop connecting the two
ends, there is NOMINALLY no voltage diff between the ends but if the
loop is in a magenttic field there can be a small difference and when
you connect the ends together, the small voltage can create a large
current because the resistance is so low.

Now calculate how much current is created by that magnetic field.
Once numbers are provided in that post (and that also comes from
experience), then the few feet of wire must never create that kind of
voltage. Nothing even approaching 1 volt should exist. Even more
than two volts between electronics and the mains breaker box is
completely unacceptable for human safety. Magnetic fields on short AC
cords create 1 volt. Nonsense.

Properly noted is that wire is an electronic component - which is
why the safety ground must join at a common point nearby all
components.

Safety ground performs many functions beyond protecting human life.
Safety ground between two adjacent components at 1 volt? Complete
nonsense or an indication of a serious problem that is also a major
human safety threat. If both components are properly safety grounded
to a common point, then voltage differences created by massive
magnetic fields are so low as to not cause measureable hum.

First, safety ground serves many functions beyond human safety - if
properly connected.

Second, magnetic fields do create such currents. Current that must
be so trivial as to be virtually zero. Furthermore, no such massive
magnetic fields should exist there anyway. Two reasons why magnetic
fields do not create as speculated without numbers. Remove the
hypothetical massive magnetic field generator that is drawing maybe
100 watts if those hypothetical fields exist. Another example of
curing the problem rather than its symptoms.

Meanwhile, if the safety grounds are properly connected (and that
includes how grounds connect inside each component), then no
significant voltage difference should exist on that signal cable. The
Radio Shack transformer is blocking currents due to a design
deficiency that must never exist if all safety grounds are properly
connected (ie not compromised by a UPS) and if a design or component
defect does not exist inside one component.

Fix the problem. Do not invent excuses or cure symptoms. Magnetic
fields creating such currents on short wires is only speculation not
supported by numbers or cured by removing a defective massive field
generator that should never exist. Safety ground serves many
functions beyond human safety - including no hum on signal wires.
That is why safety grounds meet at an adjacent and common point -
which is clearly not required for human safety - which is clearly done
to make those currents blocked by the Radio Shack isolator not
possible.

Maybe safety ground is perverted by the UPS as the OP suggests.
Therefore the RS isolator is curing a symptom. Instead, cure the
problem. No such noise currents should exist if all components are
properly safety grounded to a common and nearby point.

Bill,
You are working too hard here. It is all perfectly normal, maybe not
desirable, but normal.
I am going to set this up as I understand it in a U.S. residential
situation, and most businesses are the same; Power enters the building and
goes through a distribution system, a fuse or circuit breaker panel to be
subdivided to the various paths around your home/office. usually in this box
is a common point, center tap of the 240 volt, Ground and Neutral common on
this one buss. Now arbitrarily I have a duplex receptacle at the end of 100
feet of #14 copper wire, if I put a 10 amp load on this circuit, there will
be a small voltage drop on the wires. a quick look up in the Engineers book
says for hard drawn copper wire 100 feet Equals .25 ohms of resistance, all
normal, all usual, but this voltage drop works out to be 2.5 volts. If I
started out with 120 volts now I only have 118.5 volts, not bad normal. Now
on the neutral return path to the box is now 2.5 volts above ground
potential, still normal, leaves me working with 115 volts at a 10 amp load.
measuring from the safety ground which has no load, and is at ground
potential to the neutral pin of the receptacle 2.5 volts of AC, this only
becomes a problem when I plug in a 2 prong plug that assumes that neutral is
at zero volts and it isn't. no harm no fowl normal but it does hum like the
dickens when you plug in an unbalanced audio with 2.5 volts of hum on the
ground and your amplifier just knows that since it has a grounded 3 wire
plug on it there will be a bit of current flowing on the shield. Balanced
audio is so good because of the common mode rejection that it has. If you
want to go unbalanced the only thing you can do is break the ground loop
circuit by option "A" a line voltage (Mains) isolation/insulation
transformer or option "B" transformer coupling the audio cut. to break the
ground loop. A $100 transformer for the mains or the RadioShack wonder for
$16.99. Like I said all normal, all safe, not a fantastic fix, but
reasonable.
Now if you still want something to worry about, I had a great Aunt that
worried about the electricity leaking out of the unused receptacles, think
about it, have a nice day!
Dave_________



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