Equipment Ground Conductor (EGC) on an overhead line

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philly

Senior Member
I'm involved in rebuild of a customer owned industrial sub that has a 13.2kV feeder from secondary of substation down to the plant's main incoming switchgear. Utility metering is on primary of substation transformer so everything from transformer down falls under NEC purview in my opinion.

The 13.2kV feeder from the sub will be underground cable before it transitions to a new short overhead line to join an existing overhead (ASCR cable) line that is run into the existing facility.

Am I correct in understanding that the NEC requires a separate EGC and thus my new OH line portion will need to have a ground wire (UG portion of cable will have an EGC run up to pole)? In these cases is the OH ground typically installed as a shield above ASCR phase conductors, or below it similar to a utility Distibution neutral?

It also appears that the existing OH line going into the plant does not have any sort of separate EGC? This was a much older installation and at one point in time looks like system may have been LRG grounded (its solidly grounded now). Is there any sort of exception in NEC for older installations that did not have an EGC? Is there an approach to a situation like there where one does not exist for OH cables traversing several hundred yards before getting to facility?
 
philly said:
I'm involved in rebuild of a customer owned industrial sub that has a 13.2kV feeder from secondary of substation down to the plant's main incoming switchgear. Utility metering is on primary of substation transformer so everything from transformer down falls under NEC purview in my opinion.

The 13.2kV feeder from the sub will be underground cable before it transitions to a new short overhead line to join an existing overhead (ASCR cable) line that is run into the existing facility.

Am I correct in understanding that the NEC requires a separate EGC and thus my new OH line portion will need to have a ground wire (UG portion of cable will have an EGC run up to pole)? In these cases is the OH ground typically installed as a shield above ASCR phase conductors, or below it similar to a utility Distibution neutral?

It also appears that the existing OH line going into the plant does not have any sort of separate EGC? This was a much older installation and at one point in time looks like system may have been LRG grounded (its solidly grounded now). Is there any sort of exception in NEC for older installations that did not have an EGC? Is there an approach to a situation like there where one does not exist for OH cables traversing several hundred yards before getting to facility?
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Rely on earth to clear mv ground fault, no egc, safety hazard and code violation
 
philly said:
I'm involved in rebuild of a customer owned industrial sub that has a 13.2kV feeder from secondary of substation down to the plant's main incoming switchgear. Utility metering is on primary of substation transformer so everything from transformer down falls under NEC
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philly said:
Am I correct in understanding that the NEC requires a separate EGC
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Over 1000V you have a buffet of allowed grounding methods or 'earthing system' options under the NEC so its important to understand how the power source (substation transformer) is designed and stick with a method.
Unfortunately the NEC does not cover this well and lacks simple clear definitions.
First question I ask myself; is it connected to earth or isolated, resistance / reactance grounded etc?
Then I consider the fault clearing path, is there metallic path (wire) back to the grounded point on the source in your case the cable shield are there protective relays on the MV system?
For a substation transformer with a wye secondary thats solidly grounded to earth (Terra) and has a conductor in the feeder ('Neutral') grounded at the substation (connected to the GES) the NEC allows you to use a combined neutral and equipment ground or a 'Terra' + 'Neutral' - combined system TN-C, in 250 part X.
The NEC is all over the place with grounding terms to describe types of grounding systems or 'earthing systems' in part X of 250 they call TN-C 'Multi Grounded Neutral' or MGN.
Also 250 part X allows you to keep separate equipment ground and neutral functions like we do with 1000V or less, known as a Terra Neutral separate or TN-S, they call this 'single point grounded' in that article.
You can pick a end point on an TN-C system call that the last multi grounded point, establish a GES, switch between TN-C to TN-C-S, on a common utility system this would be most often be the service disconnect.
 
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If you're in PECO land, the neutral is probably solidly grounded at the source. It's good to have an MGN run with the phase conductors so there is a GF path back to the source neutral point.
 
philly said:
It also appears that the existing OH line going into the plant does not have any sort of separate EGC? This was a much older installation and at one point in time looks like system may have been LRG grounded (its solidly grounded now). Is there any sort of exception in NEC for older installations that did not have an EGC? Is there an approach to a situation like there where one does not exist for OH cables traversing several hundred yards before getting to facility?
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The EGC should be running about 5' down from the phase conductors on the pole. Or it could just be the messenger that any secondary conductors are hanging on. If shielded cables are coming down off the pole, then the concentric neutrals ought to be bonded to it.
 
JoeStillman said:
The EGC should be running about 5' down from the phase conductors on the pole. Or it could just be the messenger that any secondary conductors are hanging on. If shielded cables are coming down off the pole, then the concentric neutrals ought to be bonded to it.
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Thanks. If no messenger would this just typically be an smaller ASCR type cable? The cable coming down from pole will have a an equipment ground conductor as well as a tape shield on the MV cable both of which will be bonded to this EGC.
 
See NEC art.230 Services.
See Part II. Overhead Service Conductors. Art.230.23 Size and Ampacity.
(C) Grounded Conductors. From here see 250.24 F Ungrounded system grounding connection. From here see 250.52 Grounding Electrodes
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Julius Right said:
See NEC art.230 Services.
See Part II. Overhead Service Conductors. Art.230.23 Size and Ampacity.
(C) Grounded Conductors. From here see 250.24 F Ungrounded system grounding connection. From here see 250.52 Grounding Electrodes
View attachment 2580097
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These would not be considered "service conductors" since they are downstream of utility POC. These would be considered feeders.

Also the most recent system that we are replacing and the new transformer being installed will be solidly grounded and thus require an equipment ground conductor. Perhaps original older system was ungrounded and when they more recently changed to the solidly grounded system they are using now never gave thought to the lack of EGC and have just been operating it that way.
 
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