Equipment Grounding for Ungrounded System

[ronaldrc]

Which is why a GFCI would be worthless on an ungrounded system.

It will not be needed, nor would it function under normal conditions.[/QUOL

Larry

I Couldn't agree with you more. And as long as this is just a hypothetical
idea and know one thinks we should go with a ungrounded residential system
I don't see a problem.

Do you agree with this? As long as we have underground branch circuits
in residential which will eventually fault to the earth we will need to
leave the solidly grounded system as is?

Because with the solidly grounded three wire single phase system the grounded neutral is not as dangerous as a grounded line #1 or line #2 would
be. With one of the lines to ground you have a shock hazard of 240 volts instead of the 120 volts we have now.

When any conductor makes contact with the earth then you would need the GFI receptacle outside. I have went on many service calls where the wind has blown a three limb down and knocked one of the service drop conductors down onto the wet ground during a thunderstorm.I have also repaired nm romex that has come loose from the floor joist in crawl spaces and faulted in the dirt. Events like this are always going to happen.

I think this example gives a better idea of how the fault current is actually flowing at least it does for me.

Thanks for reading

 

[bobby ocampo]

Do you understand 250.142(B)?

May you please state 250.142 and interpret it for me?

 

[iwire]

May you please state 250.142 and interpret it for me?

Last I knew the NEC was available on line at the NFPA

www.nfpa.org

 

[bobby ocampo]

Connection to earth is used to reduce the potential of the energized metal piece to earth potential. This is also the purpose of connecting the neutral of the solidly grounded system so that potential of the current carrying conductor will be limited to line to ground fault.

Where are you getting this in the NEC?

Hope you will answer this questions.

What do you think is the purpose of the equipment grounding in an UNGROUNDED SYSTEM where there is no single line to ground fault current but if one of the conductor touching the metal piece it will have a potential equal to the line-to-neutral voltage if the EGC is not connected to earth.

What do you think is the purpose of ground fault protection for OCPD of 1000 amps and above of more than 150 volts to ground? What do you think is the fault current in an ARCING GROUND FAULT?

 

[iwire]

Hope you will answer this questions.

What do you think is the purpose of the equipment grounding in an UNGROUNDED SYSTEM where there is no single line to ground fault current but if one of the conductor touching the metal piece it will have a potential equal to the line-to-neutral voltage if the EGC is not connected to earth.

What do you think is the purpose of ground fault protection for OCPD of 1000 amps and above of more than 150 volts to ground? What do you think is the fault current in an ARCING GROUND FAULT?

Bobby FOCUS! stay on one topic at a time.

The requirement for GFP for large feeders and services has nothing to do with an earth connection.

 

[weressl]

It is in the OHMS law section of the NEC. Have you ever heard of this section??

Yeah, yeah, yeah, I got it!

When you sit in lotus position, take deep, slow breaths, close your eyes and from the depth of your chest you repeat: Oooooooooohhhhhmmmmmmm

 

[don_resqcapt19]

IF that is the case, then it is only true to SINGLE ground rods and not industrial or commercial use structures where

1. muiltipoint grounding rods exist with interconnecting grounding cables between them
2. steel structures in industrial plants where the 'ground' is steel decking or grating.

If the above is true then the Code is negligent in addressing other than single family dwelling installations.

The 'shells' exist, however they are immaterial since there is only a linear path exist between the ground rod and the knee of the poor fella...

Both the testing and the IEEE table are based on a single rod, however the same thing happens as you move away from any grounding electrode system. With large conductive structures all of the bonded points, with the exception of the faulted point are at the same potential under fault conditions. However the actual faulted equipment will have an elevated voltage as measured to other bonded points a result of the voltage drop in the EGC that is carrying the fault current. This voltage will exist only as long as the fault exists and that should be a very short time. With multiple bonding points and fault clearing paths in these larger systems, the voltage drop may be less than when a single EGC is the fault clearing path is used. With a large fault current there is limited fault current flowing on the remote paths as a result of the increased impedance of these paths that is caused by the physical separation between the supply and return paths. The connection to earth does nothing to make an equal potential under fault conditions. Even in the large substation grounding mats, it is the closely spaced conductors of the mat and not the connection to earth that creates the equal potential area.

 

[iwire]

Both the testing and the IEEE table are based on a single rod,

Don, how was your test or Mike's test done with a single rod?

I assume you did not use a isolation transformer so there where many multiple electrodes spread out around your tests.

 

[tryinghard]

Which is why a GFCI would be worthless on an ungrounded system.

It will not be needed, nor would it function under normal conditions.

I understand and agree to this.

I think there are some that are misusing the term "ungrounded system" as a system that has a bonded transformer but is missing the earth connection, this is not an ungrounded system it is an "incorrecly installed system" and a code violation!

An ungrounded system is intentionally devoid of any transformer bond and neutral. It is common and legal, these are used for critical machinery, typically industrially but also commercially.

 

[iwire]

An ungrounded system is intentionally devoid of any transformer bond and neutral. It is common and legal, these are used for critical machinery, typically industrially but also commercially.

IMO that is exactly the type of system this thread is about.

Look at the thread title and Bobby's posts at the start if the thread.

 

[tryinghard]

It is in the OHMS law section of the NEC. Have you ever heard of this section??

I understand the resistance in earth is unknown at any given moment. I agree with the NEC that earth cannot be used as an effective ground fault path and I always have.

Don?t think for one second that I am advocating the use of earth this way.

Of course I have heard of Ohm?s law! What do you mean with your question?

 

[tryinghard]

May you please state 250.142 and interpret it for me?

Your not going to be effective at this site without your code book! This is an NEC forum.

 

[weressl]

Both the testing and the IEEE table are based on a single rod, however the same thing happens as you move away from any grounding electrode system. With large conductive structures all of the bonded points, with the exception of the faulted point are at the same potential under fault conditions. However the actual faulted equipment will have an elevated voltage as measured to other bonded points a result of the voltage drop in the EGC that is carrying the fault current. This voltage will exist only as long as the fault exists and that should be a very short time. With multiple bonding points and fault clearing paths in these larger systems, the voltage drop may be less than when a single EGC is the fault clearing path is used. With a large fault current there is limited fault current flowing on the remote paths as a result of the increased impedance of these paths that is caused by the physical separation between the supply and return paths. The connection to earth does nothing to make an equal potential under fault conditions. Even in the large substation grounding mats, it is the closely spaced conductors of the mat and not the connection to earth that creates the equal potential area.

My argument pertains to the even when the EGC is failed and not present.

 

[weressl]

Don?t think for one second that I am advocating the use of earth this way.

I don't think anyone is suggesting that.

 

[tryinghard]

Hope you will answer this questions.

What do you think is the purpose of the equipment grounding in an UNGROUNDED SYSTEM where there is no single line to ground fault current but if one of the conductor touching the metal piece it will have a potential equal to the line-to-neutral voltage if the EGC is not connected to earth.

I have pointed this out a few times already.

It is spelled out in 250.4(B)(2) through (4)! This is why a journeyman electrician provides equipment grounding (bonds non current carrying items) on an ungrounded system. This is really not that complicated!

 

[tryinghard]

I don't think anyone is suggesting that.

The earth is not a back up route if equipment grounding fails!

 

[winnie]

This thread remains interesting and reasonably professional. By the normal standards of this forum, it should remain open.

This thread is also a mis-mash of different topics: metallic bonding, earth soil connections, high voltage distribution, low voltage systems, ungrounded, impedance grounded, solidly grounded.....

I suggest that this thread be closed with an invitation to members to start focused threads on the individual topics above.

I would suggest that those who choose to open such 'focused' threads explicitly limit them by taking the time to state the context that they are considering. Are you specifically asking about the value of the connection to soil? At what voltage? Are you asking what the NEC requires, or are you trying to point out a flaw in the NEC? Don't ask a one liner question and expect others to make the same basic assumptions that you are making; state explicitly your basic assumptions.

Just my opinion. I've liked this thread so far, though with the frequent feeling that I one person asks a questions and another person answers a different question!

-Jon

 

[iwire]

I suggest that this thread be closed with an invitation to members to start focused threads on the individual topics above.

Agreed, it is done.

I would suggest that those who choose to open such 'focused' threads explicitly limit them by taking the time to state the context that they are considering.

A great suggestion.