I am working on a job where a cogen facility is being upgraded with two (2) new turbine generators. Each one will have a feeder from a 1200A circuit breaker to a substation some 2500 feet away. We will be installing two (2) 3C-500 kcmil cables along side four (4) existing 3C-500 kcmil cables in a cable tray so that each feeder will consist of three (3) sets 3C-500. Currently a bare copper ground conductor (not sure if it's 2/0 or 3/0) is run in the tray with the four (4) existing feeder cables. We are being asked to install an additional grounding conductor (3/0) in the tray because the "ampacity of the tray" has increased. I'm not sure that a second conductor is warranted, but I don't know how to research this. Can you give me any suggestions?
MV feeder grounding conductor
- Thread starter mglennon
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: MV feeder grounding conductor
You need to take a look at 250.122(F).
Don
You need to take a look at 250.122(F).
Don
cripple
Senior Member
- Location
- Santa Fe, New Mexico
Re: MV feeder grounding conductor
The equipment grounding conductor shall be sized per table 250.122, and must full size in each multiple parallel raceways. The 3/0 cannot be used as the equipment grounding conductor if the existing cable and the newly installed cable have an equipment grounding conductor within the sheath of the cable. Section 250.122(F)(2) applies to cables that are installed in parallel. Because cable assemblies are manufactured in standard conductor size configurations, the equipment grounding conductor in a cable is properly sized for some circuit arrangements. However, if the cable is used in large-capacity parallel circuits, the equipment grounding conductor in each cable may not be sized in accordance with Table 250.122. To address this problem, 250.122(F)(2) permits the sizing of the equipment grounding conductor within a multiconductor cable to be based on the trip setting of an equipment ground-fault device. This method of protection is only permitted where the installation will be serviced by qualified personnel and the ground-fault device is specifically listed for this purpose. The trip setting of the ground-fault protection of equipment (GFPE) cannot exceed the ampacity of a single ungrounded conductor installed in one of the parallel cables. This rule precludes the need to manufacture multiconductor cables with equipment grounding conductors that are sized for a specific parallel circuit configuration.
The equipment grounding conductor shall be sized per table 250.122, and must full size in each multiple parallel raceways. The 3/0 cannot be used as the equipment grounding conductor if the existing cable and the newly installed cable have an equipment grounding conductor within the sheath of the cable. Section 250.122(F)(2) applies to cables that are installed in parallel. Because cable assemblies are manufactured in standard conductor size configurations, the equipment grounding conductor in a cable is properly sized for some circuit arrangements. However, if the cable is used in large-capacity parallel circuits, the equipment grounding conductor in each cable may not be sized in accordance with Table 250.122. To address this problem, 250.122(F)(2) permits the sizing of the equipment grounding conductor within a multiconductor cable to be based on the trip setting of an equipment ground-fault device. This method of protection is only permitted where the installation will be serviced by qualified personnel and the ground-fault device is specifically listed for this purpose. The trip setting of the ground-fault protection of equipment (GFPE) cannot exceed the ampacity of a single ungrounded conductor installed in one of the parallel cables. This rule precludes the need to manufacture multiconductor cables with equipment grounding conductors that are sized for a specific parallel circuit configuration.
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