Grounding of pole line 12.47kV wye circuit

J

joshtrevino

Member
Location
Beaumont, TX
I have a customer who has an incoming three phase 12.47kV circuit (3 bare phase conductors on crossarms with a static/neutral below the phases) coming into the facility from the utility. The circuit passes through the utility metering point and becomes customer owned (premises wiring) at a customer owned recloser. The circuit (now customer owned) continues into the facility in the same configuration described above feeding many customer owned three phase transformers (with both delta and wye primary connections). There are also single phase transformers for lighting, recloser control power, etc fed by the 12.47kV circuit. It seems to me that the neutral/static is also functioning as the EGC (equipment ground conductor) back to the source. For example, there is no separate EGC for the recloser housing. I am working on a project for which I will be modifying this system and want to understand how this configuration fits into the NEC, especially article 250. I know outside the facility the utility is governed by NESC, but inside the facility NEC is the governing standard. What article in NEC (2023 please) allows for this grounding configuration for a medium voltage pole line circuit?

Please let me know if I need to provide further details or clarity.
 
joshtrevino said:
I have a customer who has an incoming three phase 12.47kV circuit (3 bare phase conductors on crossarms with a static/neutral below the phases) coming into the facility from the utility. The circuit passes through the utility metering point and becomes customer owned (premises wiring) at a customer owned recloser. The circuit (now customer owned) continues into the facility in the same configuration described above feeding many customer owned three phase transformers (with both delta and wye primary connections). There are also single phase transformers for lighting, recloser control power, etc fed by the 12.47kV circuit. It seems to me that the neutral/static is also functioning as the EGC (equipment ground conductor) back to the source. For example, there is no separate EGC for the recloser housing. I am working on a project for which I will be modifying this system and want to understand how this configuration fits into the NEC, especially article 250. I know outside the facility the utility is governed by NESC, but inside the facility NEC is the governing standard. What article in NEC (2023 please) allows for this grounding configuration for a medium voltage pole line circuit?

Please let me know if I need to provide further details or clarity.
Click to expand...
Where is the service disconnect?
 
electrofelon said:
You can use the neutral for grounding per the NEC if you meet the requirements, see 250.184. otherwise you would need a separate neutral and EGC just like you would for low voltage.
Click to expand...
electronfelon, it seems that we have a "multigrounded neutral system" per 250.184.C, but I do not see that the language allows using the neutral as the low impendence path to ground instead of an EGC. Is this implied? Is it explicitly stated elsewhere? Not challenging you but honestly asking.
 
joshtrevino said:
electronfelon, it seems that we have a "multigrounded neutral system" per 250.184.C, but I do not see that the language allows using the neutral as the low impendence path to ground instead of an EGC. Is this implied? Is it explicitly stated elsewhere? Not challenging you but honestly asking.
Click to expand...
I'll have to look over the wording when I get more time, but my initial thought it is just implied. The wording in part X is pretty sloppy and vague with the term "grounding". Note the title of part X says "grounding of systems and circuits".

joshtrevino said:
Per the single line diagram the utility has a fuse upstream of the metering point. Utility fuse -> Utility Meter ->Customer Recloser.
Click to expand...
So where is the service disconnect?😉
 
joshtrevino said:
electronfelon, it seems that we have a "multigrounded neutral system" per 250.184.C, but I do not see that the language allows using the neutral as the low impendence path to ground instead of an EGC. Is this implied? Is it explicitly stated elsewhere? Not challenging you but honestly asking.
Click to expand...
There have been some changes recently with the over 1000 volts stuff what NEC version are you on? In the 2023 NEC see 235.106, 250.190 and 495.37.
The NEC wording describing the relationship of electrical systems and ground is wordy and out of date, I wish they adopted the IEC terminology for earthing systems in the over 1000V stuff, its pretty intuitive;

The first letter indicates the relationship between the power-supply (transformer, generator, SDS, battery .. etc) and ground (dirt):
"T" = Direct connection of a point on the power-supply to a Grounding Electrode system (GES). Commonly seen on a center tap split phase, wye, corner grounded delta transformer.
"I" = Non grounded All live parts isolated from Earth or impedance grounded.

The second letter indicates which wire serves as the equipment ground (bonding the exposed-conductive-parts of the installation, and Earth):

"N" = Direct connection between a point on the power-supply and a GES. Typically the neutral point of a wye transformer, or center tap of split phase.

"T" = GES is totally independent of a power-supply connection to Earth. (Common in Japan not here, other than a perhaps a ungrounded DC PV system)

Subsequent letter(s) indicate:
"S" = Neutral and equipment ground functions provided by separate conductors.
"C" = Neutral and equipment ground functions provided by the same single conductor.

Some common examples are;
A typical utility system here is TN-C
A NEC service - main breaker - feeder system is TN-C-S
A NEC SDS is TN-S
 
joshtrevino said:
electronfelon, it seems that we have a "multigrounded neutral system" per 250.184.C, but I do not see that the language allows using the neutral as the low impendence path to ground instead of an EGC. Is this implied? Is it explicitly stated elsewhere? Not challenging you but honestly asking.
Click to expand...
You are not an electric utility, don't try to act one.
We are governed by the NEC. For the vast majority of circuits the NEC does not allow you to use the neutral instead of the EGC.
 
You must log in or register to reply here.
Top