Grounded Conductor for 15KV Sevices
- Thread starter jwilson
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Re: Grounded Conductor for 15KV Sevices
You say this is customer installed from a utility pole. Where is this system metered? The rules change depending on what side of the meter or service point we are talking about. How is the system you are connecting to configured? Is it ungrounded? Is it a common neutral muti grounded system?
250.24(B) specifically states it applies to grounded systems operating at less than 1000 volts. It does not apply in your case. Can you supply a little more info on the system you are dealing with?
You say this is customer installed from a utility pole. Where is this system metered? The rules change depending on what side of the meter or service point we are talking about. How is the system you are connecting to configured? Is it ungrounded? Is it a common neutral muti grounded system?
250.24(B) specifically states it applies to grounded systems operating at less than 1000 volts. It does not apply in your case. Can you supply a little more info on the system you are dealing with?
- Location
- Illinois
- Occupation
- retired electrician
Re: Grounded Conductor for 15KV Sevices
I see no need for a grounded conductor, but you do need an EGC. The cable shield is often too small to serve as the EGC.
Don
I see no need for a grounded conductor, but you do need an EGC. The cable shield is often too small to serve as the EGC.
Don
Re: Grounded Conductor for 15KV Sevices
I agree with Don that an EGC is needed, but I'm trying to logically work my way thru the NEC to present arguments to the designer, who relys on NEC 250.24(B, which states a grounded conductor is required for up to 1000 volts, thereby excluding a 15KV system.
Where does the Code require a grounded cond, or EGC for systems above 1000 volts?
I agree with Don that an EGC is needed, but I'm trying to logically work my way thru the NEC to present arguments to the designer, who relys on NEC 250.24(B, which states a grounded conductor is required for up to 1000 volts, thereby excluding a 15KV system.
Where does the Code require a grounded cond, or EGC for systems above 1000 volts?
- Location
- Illinois
- Occupation
- retired electrician
Re: Grounded Conductor for 15KV Sevices
JW,
Look at 250.180 and 250.190. The shield may or may not be large enough to act as the EGC. The printed version of Southwire Power Cable Handbook has some extensive calculations that you can do to see if the ampacity of the shield is high enough to safely clear the fault. Unfortunately that section of the handbook is not available online.
Dereck,
The shield is intented to eliminate tracking and arcing discharges along the cable surface and to prevent a hazardous potential from accumulating on the surface of insulation. You can find some information in Southwire's Power Cable Handbook near the bottom of the page.
Bennie,
The NEC does cover this installation, but I agree it does not do so in much detail and that the NESC and engineering sources should also be consulted.
Don
JW,
Look at 250.180 and 250.190. The shield may or may not be large enough to act as the EGC. The printed version of Southwire Power Cable Handbook has some extensive calculations that you can do to see if the ampacity of the shield is high enough to safely clear the fault. Unfortunately that section of the handbook is not available online.
Dereck,
The shield is intented to eliminate tracking and arcing discharges along the cable surface and to prevent a hazardous potential from accumulating on the surface of insulation. You can find some information in Southwire's Power Cable Handbook near the bottom of the page.
Bennie,
The NEC does cover this installation, but I agree it does not do so in much detail and that the NESC and engineering sources should also be consulted.
Don
Re: Grounded Conductor for 15KV Sevices
PGE, SoCal Edison, PP@L, and many other utility companies retain authority on feeders of this voltage. It is a legal liability concern.
The NESC requires a burial depth greater than the NEC. A cable buried under the NEC will be a liability for the owner, in the event of problem.
My statement about not being within the jurisdiction of the NEC, is correct in many areas.
Regardless of ownership.
PGE, SoCal Edison, PP@L, and many other utility companies retain authority on feeders of this voltage. It is a legal liability concern.
The NESC requires a burial depth greater than the NEC. A cable buried under the NEC will be a liability for the owner, in the event of problem.
My statement about not being within the jurisdiction of the NEC, is correct in many areas.
Regardless of ownership.
Re: Grounded Conductor for 15KV Sevices
To get back to the original topic.
The MGN must be complete to each transformer. The MGN must connect to the tank and X-O of the secondary.
Multi ground neutral to be grounded with an electrode at transformer.
The semi-con shield on medium voltage cable is for containing the energy field produced by the magnetic field.
[ March 20, 2003, 02:03 PM: Message edited by: bennie ]
To get back to the original topic.
The MGN must be complete to each transformer. The MGN must connect to the tank and X-O of the secondary.
Multi ground neutral to be grounded with an electrode at transformer.
The semi-con shield on medium voltage cable is for containing the energy field produced by the magnetic field.
[ March 20, 2003, 02:03 PM: Message edited by: bennie ]
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