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Earth Ground

APC UPS for Home and Office Forum

Schneider Electric support forum for our APC offers including Home Office UPS, Surge Protectors, UTS, software and services and associated products designed to share knowledge, installation, and configuration.

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iamsand_apc
Crewman
Crewman
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146

Earth Ground

This was originally posted on APC forums on 4/12/2007


I read an excellent APC article (White Paper #21) about neutral and ground. It was not explained though, exactly why the neutral is actually connected to the earth. The explination given for the safety of having exposed metal equipment connected with a ground wire that is ultimately connected to the neutral at the service panel does not explain the reason for an earth connection. If a hot conductor touched the metal case of equipment which has a ground wire, it would create a short circuit and trip the breaker, regardless of a physical connection to the earth. So why do we have these "earth" connections? It seems like all they do is offer a path back to neutral if a person is touching earth and an exposed hot connector. Where is the added safety in that?


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BillP
Administrator Administrator
Administrator
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146

Re: Earth Ground

This reply was originally posted by Steve on APC forums on 5/30/2007


The earth ground is not inherently negative or positive. It is simply that there can be potential between any 2 points in ground. When we are dealing with power coming from AC lines, hot is not positive. Voltage on an AC line cycles positive to negative and back again 60 times per second. No, I don't believe a battery would not discharge itself however the generation and distribution of AC voltage differs quite a bit from a stand-alone battery.

Ground is not required to regulate the voltage between the hots or from hot to neutral. You however may be touching ground when holding on to a rack or standing on the floor. This is the safety aspect. If there is a short on a piece of equipment, the outer case (if it is metal) could become energised. Since the outter case is grounded, the power will simply pass to ground. There is basically a short circuit now from your device's metal case to ground. That short is the path of least resistance and current will flow that way.

If the system was not grounded, you would create the path of least resistance if you touched the outer case.

As for the power company using ground to regulate the voltage between the 2 hot legs, it does not. I'm sorry if I was unclear about that. Transformers are used to create the voltages that come into your house and the neutral. As long as the power does not fluctuate and everything is as it is supposed to be, there will be 120 volts from each hot to neutral and 240 from one hot to the other.

The neutral starts there and does not travel from the generation facility. When you see power lines with 3 wires, you are actually seeing 3 hot legs that are 120 degrees out of phase.

There is always voltage present in the Earth however. The Earth is also a conductor. The simple fact is that whenever there is a potential difference between any 2 conductors, it is possible for current to flow.

It looks like you're looking more into the theoretical aspect of grounding rather than requirements or electrical codes. If you're really into the theory of it, perhaps you could read up on Nikola Tesla. I believe he theorized (among many other things) using the Earth itself as a power source. No generators needed. Simply using the differences in potential that exist between 2 points in ground as an electrical source.
There's a lot of info on him here:
http://en.wikipedia.org/wiki/Nikola_Tesla

Here are a few other links that I've found that seem to go into grounding in much more depth. Maybe they can be of help:
http://www.pfeiffereng.com/Principals%2520of%2520Electrical%2520Grounding.pdf
http://www.epanorama.net/documents/groundloop/why_grounding.html

See Answer In Context

3 Replies 3
BillP
Administrator Administrator
Administrator
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146

Re: Earth Ground

This reply was originally posted by Steve on APC forums on 5/23/2007


No matter if you have a neutral to ground bond or not, if you touch ground and a hot leg at the same time, you're gonna get zapped. If there was no neutral to ground bond, there's also the potential that you'd get zapped if you touched neutral as well. With the bond, that won't happen (when touching neutral anyway).

The power companies can only regulate the power between 2 hot legs. A transformer will then give you the neutral. In a home environment, that's simply a middle point on the main 240 volt power and it gives you (2) 120 volt sources (each hot to neutral).

With the neutral to ground bond, that also ensures that you have (2) hot legs at 120 volts with respect to ground as well. Without that bond, the voltage from neutral to ground can not be regulated and in turn, the voltage between hot and ground would not be regulated.

Between any 2 points on ground, there is a chance for voltage. The farther away the 2 points being measured, the more potential there is. If your utility pole/transformer is grounded, it's close to your house, and you measure voltages at your electrical service entrance, you'll probably see only a little voltage from neutral to ground. The farther away you are from that transformer, the more voltage you're likely to see.

Most electrical equipment can deal with a few extra volts. Many of todays electronic equipment however can be very sensitive to voltages between neutral and ground especially.

iamsand_apc
Crewman
Crewman
0 Likes
0
146

Earth Ground

This was originally posted on APC forums on 4/12/2007


I read an excellent APC article (White Paper #21) about neutral and ground. It was not explained though, exactly why the neutral is actually connected to the earth. The explination given for the safety of having exposed metal equipment connected with a ground wire that is ultimately connected to the neutral at the service panel does not explain the reason for an earth connection. If a hot conductor touched the metal case of equipment which has a ground wire, it would create a short circuit and trip the breaker, regardless of a physical connection to the earth. So why do we have these "earth" connections? It seems like all they do is offer a path back to neutral if a person is touching earth and an exposed hot connector. Where is the added safety in that?

BillP
Administrator Administrator
Administrator
0 Likes
0
147

Re: Earth Ground

This reply was originally posted by Steve on APC forums on 5/30/2007


The earth ground is not inherently negative or positive. It is simply that there can be potential between any 2 points in ground. When we are dealing with power coming from AC lines, hot is not positive. Voltage on an AC line cycles positive to negative and back again 60 times per second. No, I don't believe a battery would not discharge itself however the generation and distribution of AC voltage differs quite a bit from a stand-alone battery.

Ground is not required to regulate the voltage between the hots or from hot to neutral. You however may be touching ground when holding on to a rack or standing on the floor. This is the safety aspect. If there is a short on a piece of equipment, the outer case (if it is metal) could become energised. Since the outter case is grounded, the power will simply pass to ground. There is basically a short circuit now from your device's metal case to ground. That short is the path of least resistance and current will flow that way.

If the system was not grounded, you would create the path of least resistance if you touched the outer case.

As for the power company using ground to regulate the voltage between the 2 hot legs, it does not. I'm sorry if I was unclear about that. Transformers are used to create the voltages that come into your house and the neutral. As long as the power does not fluctuate and everything is as it is supposed to be, there will be 120 volts from each hot to neutral and 240 from one hot to the other.

The neutral starts there and does not travel from the generation facility. When you see power lines with 3 wires, you are actually seeing 3 hot legs that are 120 degrees out of phase.

There is always voltage present in the Earth however. The Earth is also a conductor. The simple fact is that whenever there is a potential difference between any 2 conductors, it is possible for current to flow.

It looks like you're looking more into the theoretical aspect of grounding rather than requirements or electrical codes. If you're really into the theory of it, perhaps you could read up on Nikola Tesla. I believe he theorized (among many other things) using the Earth itself as a power source. No generators needed. Simply using the differences in potential that exist between 2 points in ground as an electrical source.
There's a lot of info on him here:
http://en.wikipedia.org/wiki/Nikola_Tesla

Here are a few other links that I've found that seem to go into grounding in much more depth. Maybe they can be of help:
http://www.pfeiffereng.com/Principals%2520of%2520Electrical%2520Grounding.pdf
http://www.epanorama.net/documents/groundloop/why_grounding.html