Two grounds making me nervous

Lurlene · 10-29-2010, 02:17 PM

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?

jbfan · 10-29-2010, 02:22 PM

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

joed · 10-29-2010, 02:57 PM

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.

Lurlene · 10-29-2010, 05:08 PM

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.

nap · 10-29-2010, 05:47 PM

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.

a7ecorsair · 10-29-2010, 06:31 PM

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.

nap · 10-29-2010, 07:31 PM

Quote:

Originally Posted by a7ecorsair

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.

Speedy Petey · 10-29-2010, 09:51 PM

Oh please. Not ground loops again.

Quote:

Originally Posted by Lurlene

Well there can be current between two grounds without a fault,....

No, not if they are installed correctly.

Quote:

Originally Posted by Lurlene

.....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.

a7ecorsair · 10-29-2010, 11:10 PM

Quote:

Originally Posted by nap

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.

nap · 10-30-2010, 12:58 AM

Quote:

Originally Posted by a7ecorsair

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.

a7ecorsair · 10-30-2010, 09:27 AM

Quote:

Originally Posted by nap

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.

Lurlene · 10-30-2010, 10:21 AM

Quote:

Originally Posted by Speedy Petey

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.

Lurlene · 10-30-2010, 10:44 AM

Yep, if the posters here haven't heard of problems with ground loop, then there isn't one. Thanks for your responses guys!

nap · 10-30-2010, 11:24 AM

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.

nap · 10-30-2010, 11:28 AM

Quote:

Originally Posted by Lurlene

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)

10-29-2010, 02:17 PM	#1
Lurlene Graduate of Wiring 1-2-3 Join Date: Sep 2010 Location: New Hampshire Posts: 31	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?

10-29-2010, 02:22 PM	#2
jbfan Electrical Contractor Join Date: Jun 2004 Location: Newnan GA Posts: 5,081	Two grounds making me nervous Nothing to worry about. Just make sure that the ground and neutral are separate __________________ Yes I am a Pirate, 200 years too late. "Jimmy Buffett"

10-29-2010, 02:57 PM	#3
joed Member Join Date: Mar 2005 Location: Welland, Ontario Posts: 6,104	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. __________________ Do not PM with questions that can be asked in a forum. I will not respond.

10-29-2010, 05:08 PM	#4
Lurlene Graduate of Wiring 1-2-3 Join Date: Sep 2010 Location: New Hampshire Posts: 31	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.

10-29-2010, 05:47 PM	#5
nap You talking to me? Join Date: Dec 2007 Location: sw mi Posts: 5,407	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.

Two grounds making me nervous