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Old 10-29-2010, 02:17 PM   #1
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Two grounds making me nervous


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?

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Old 10-29-2010, 02:22 PM   #2
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Two grounds making me nervous


Nothing to worry about.
Just make sure that the ground and neutral are separate

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Old 10-29-2010, 02:57 PM   #3
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Two grounds making me nervous


Curernt does not flow on the ground unless you have a fault. Current does not flow through the rods even if you have a fault. The rods are for lightning protection.
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Old 10-29-2010, 05:08 PM   #4
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Two grounds making me nervous


Well there can be current between two grounds without a fault, but if electrolysis or telluric current were a common problem, electricians would know about it.
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Old 10-29-2010, 05:47 PM   #5
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Two grounds making me nervous


With audio work, you do a lot of things to avoid noise that is not considered with a power circuit. Each has it's own rules simply because of what they are.
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Old 10-29-2010, 06:31 PM   #6
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Two grounds making me nervous


I think you are referring to a chassis ground when you are dealing with audio circuits. The term ground can have different meanings in different settings.
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Old 10-29-2010, 07:31 PM   #7
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Two grounds making me nervous


Quote:
Originally Posted by a7ecorsair View Post
I think you are referring to a chassis ground when you are dealing with audio circuits. The term ground can have different meanings in different settings.
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.
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Old 10-29-2010, 09:51 PM   #8
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Two grounds making me nervous


Oh please. Not ground loops again.


Quote:
Originally Posted by Lurlene View Post
Well there can be current between two grounds without a fault,....
No, not if they are installed correctly.


Quote:
Originally Posted by Lurlene View Post
.....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.
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Old 10-29-2010, 11:10 PM   #9
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Two grounds making me nervous


Quote:
Originally Posted by nap View Post
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.
Since we don't have a schematic, we don't know much. There are transformer power supplies where the secondary is isolated from the primary except for a RC network for filtering. The resistor in some of these is 2.2 meg.
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Old 10-30-2010, 12:58 AM   #10
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Two grounds making me nervous


Quote:
Originally Posted by a7ecorsair View Post
There are transformer power supplies where the secondary is isolated from the primary except for a RC network for filtering. The resistor in some of these is 2.2 meg.
maybe you can explain it to me but I'm not seeing the connection between ground loops and your transformer.
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Old 10-30-2010, 09:27 AM   #11
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Two grounds making me nervous


Quote:
Originally Posted by nap View Post
maybe you can explain it to me but I'm not seeing the connection between ground loops and your transformer.
I was only pointing out that in electronic components there can be a chassis ground that is not equipment ground. In most cases, this chassis ground is the DC supply return. The transformer in the power supply provides the isolation between the AC and the DC circuits.
It is similar to an AC welder. The work "ground" clamp is not connected to the EGC. There is no current path between the primary and secondary sides.
There are separate symbols to designate the two: The one on the right is chassis ground.
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Old 10-30-2010, 10:21 AM   #12
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Two grounds making me nervous


Quote:
Originally Posted by Speedy Petey View Post
Oh please. Not ground loops again.



No, not if they are installed correctly.


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.
Thanks Pete but gee you seem a bit impatient today. Hey, have you seen this forum? It's really funny. You might want to relax over there for a while.
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Old 10-30-2010, 10:44 AM   #13
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Two grounds making me nervous


Yep, if the posters here haven't heard of problems with ground loop, then there isn't one. Thanks for your responses guys!
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Old 10-30-2010, 11:24 AM   #14
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Two grounds making me nervous


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.
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Old 10-30-2010, 11:28 AM   #15
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Two grounds making me nervous


Quote:
Originally Posted by Lurlene View Post
Yep, if the posters here haven't heard of problems with ground loop, then there isn't one. Thanks for your responses guys!
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)

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