Equipment Grounding Conductors in utility plant

[Pierre C Belarge]

Smart,
Yes, all parallel paths reduce the total impedance, however it is still my understanding that the impedance of any remote path is significantly higher than that of the EGC that is run with the circuit conductors and these remote paths do not make much of a change in the total parallel impedance. They are not redundant paths for the purpose of fault clearing as they are not suitable for clearing high current faults as a result of their high impedance.

As Don has mentioned, the impedance of the conductor that is not run with the ungrounded conductors will be higher than ones installed within the same raceway as the ungrounded conductors, even if they are the same size.

 

[mivey]

...No matter how many "remote" or "separate" paths are installed most of the fault current will flow on the EGC that is run with the circuit conductors...

...They are not redundant paths for the purpose of fault clearing as they are not suitable for clearing high current faults as a result of their high impedance.

As Don has mentioned, the impedance of the conductor that is not run with the ungrounded conductors will be higher than ones installed within the same raceway as the ungrounded conductors, even if they are the same size.

I'll make one more try. I think Charlie may have given up already but here it goes: These systems are designed to handle the fault currents and they may or may not have an ECG run with the ungrounded conductors.

Read the stuff from my other two posts. These are engineered grounding systems and are not going to look like the stuff you see in the normal world as these are in the NESC world.

I have attached a picture from the IEEE Std 665-1995 (Generating Station Grounding) section 5.5.3.3, showing a system without the ECG run along with the ungrounded conductors. These grounding systems are designed to do the job, including providing a means for protective devices to function properly.

 

[don_resqcapt19]

Engineering does not change the fact that remote fault clearing paths have a significantly higher impedance than a path that is run with the circuit conductors. If the fault current is large enough the OCPD will not operate within its instantaneous trip range and maybe not within its short time range.
Now one big thing that would change this is (as shown in the previous post) the fact that a lot of these systems are not solidly grounded, they are on a high resistance or impedance grounding system there will never be a large amount of fault current.
There is a table in the IEEE Green Book that shows the increase in impedance as the source and return path are separated...I don't have my copy here at home, but as I recall, it doesn't take a lot of separation to double the impedance.

 

[mivey]

Engineering does not change the fact that remote fault clearing paths have a significantly higher impedance than a path that is run with the circuit conductors. If the fault current is large enough the OCPD will not operate within its instantaneous trip range and maybe not within its short time range.
Now one big thing that would change this is (as shown in the previous post) the fact that a lot of these systems are not solidly grounded, they are on a high resistance or impedance grounding system there will never be a large amount of fault current.
There is a table in the IEEE Green Book that shows the increase in impedance as the source and return path are separated...I don't have my copy here at home, but as I recall, it doesn't take a lot of separation to double the impedance.

No need to get the book, as I do not doubt the impedance increase. I do doubt that the system would be designed so that the OCPD would not work.

 

[Smart $]

As Don has mentioned, the impedance of the conductor that is not run with the ungrounded conductors will be higher than ones installed within the same raceway as the ungrounded conductors, even if they are the same size.

I acknowledge both Don's and your position. Can either of you cite a reference? In my mind that just seems to defy the fundamental concepts of electricity (yes, I realize my mind works quite different than most :wink: ). I am also wondering if when we are talking EGC impedance, are we including the parallel effect of wire and raceway, and incidental paths established by common juctions and supporting means as the EGC run with conductors... or just the one wire?

 

[jy121]

Anybody bother asking if the system was high resistance grounded????