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Two grounds making me nervous

4K views 16 replies 7 participants last post by  AllanJ 
#1 ·
I will be running electricity to an outbuilding soon. Four wires going 50Ft in underground conduit from the existing panel to a detached building. The ground rods are the next step but I've got something bugging me. This could have nothing to do with electrical safety or efficiency but while studying audio circuits I was taught to only ground in only one place to avoid ground loop. Now I'm putting in a second ground at the outbuilding, and I keep thinking current will flow from one ground to the other, even though they are 50 ft apart. If I turn on a speaker or tv in the outbuilding will it buzz? Am I blowing things out of proportion? Is there some attribute of signal to noise ratio or low voltage circuits that don't apply to detached garages?
 
#8 ·
Oh please. Not ground loops again. :icon_rolleyes:


Well there can be current between two grounds without a fault,....
No, not if they are installed correctly.


.....but if electrolysis or telluric current were a common problem, electricians would know about it.
No, electricians do not normally deal with this stuff. Electronics and audio engineers do.

Ground loops are NOT an issue or problem with construction electric.
 
#7 ·
well, the thing is, that chassis ground is connected to egc. I understand Lurlene's point as it is typical procedure to connect drains at only one end of a shield. The justification as far as I understand is so that you do not create a pathway for other currents (that ground loop thing Lurlene was talking about) that might be running around in the audio equipment but only drain emf induced current that might be created as the shield is exposed to ambient emf.
 
#15 ·
You must realize what the concern with a ground loop is. It is to avoid electrical noise on a system. Due to the fact we are not transmitting any sort of signal over the power lines, ground loops are not a problem. We actually do create ground loops in various ways. It's just that they are not a concern in a power system (at least in the type of system we generally are speaking of)
 
#14 ·
well corsair, if you want to argue a point, you really should use the proper symbols for your terminology.

this is a chassis ground symbol



your symbol with the triangle pointing downward is a "signal ground" which is not the same as a chassis or earth ground.
 
#17 · (Edited)
Ground loops pose problems because the bonding conductor(s) have too much resistance producing voltage drops that are large compared with the magnitude (often less than one volt) of the audio signal. A #14 copper wire daisy chained among and securely attached to the chassis of each piece of electronic equipment almost always cures ground loop problems.

When the transformer secondary is isolated, it may still be connected to the transformer primary starting with the secondary terminal connected to the the electronic circuitry ground connected to the chassis connected to the ground wire of the power cord connected to the ground wires of the electrical system connected to the main panel neutral/ground bus bar connected to the neutral wires of the electrical system connected to the neutral wire of the power cord (finally connected to the neutral terminal of the transformer primary).

Transmitting signals over power lines depends on the signals being far enough removed from 60 Hz with the latter being filtered out by the receiving circuits. Since there may be harmonics of 60 Hz, most likely 120 Hz or 180 Hz or 240 Hz, in the power line, having the desired signals somewhat higher than that is desirable so those frequencies, too, can be filtered out without deleting portions of the desired signals.

Usually the signals are confined to the power lines connected to the same side of the 120/240 volt feed coming from just that one utility pole transformer because the latter usually won't pass the signals on to other part of the power grid. For practical purpose within a home, the signals can only propagate through about half the branch circuits namely those on one side of the 120/240 volt service. A special filter circuit can be put in the panel to get the signals over to the other side of the 120/240 volt service.
 
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