Service Conductors
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Re: Service Conductors
The building is 22 stories 298 units. Service size with NEC Demand Factors is 6000 amps more or less. If I was to make up the risers of 2-3000 amp or 3-2000 amp bus ducts fed from a 6000 amp switch board then the issue is service laterals from utility transformer to switch board. It appears to me that you practically can not put enough parallel runs (due to adjacent conductor heating) to get 6000 amps using wire and conduit.
The building is 22 stories 298 units. Service size with NEC Demand Factors is 6000 amps more or less. If I was to make up the risers of 2-3000 amp or 3-2000 amp bus ducts fed from a 6000 amp switch board then the issue is service laterals from utility transformer to switch board. It appears to me that you practically can not put enough parallel runs (due to adjacent conductor heating) to get 6000 amps using wire and conduit.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Service Conductors
I am guessing that you are talking about 6000 amps at 120/240 volts or 120/208 volts. Can you have the utility serve the building at 480 volts, and place 480 ? 120/240 step down transformers in electric rooms, say on every other or every third floor?
As to the de-rating for underground runs, that is a subject of some debate. I would be willing to go for 15 sets of 500 MCM 75C rated copper conductors, with the parallel conduits laid out in a three vertical by five horizontal pattern, with at least 7.5 inches between any two conduits. I cannot speak for the difficulty that a team of electricians might have in installing this run. Also, I would only go for this design concept because you stated that the 6000 amps is the result of an NEC service calculation. See other discussions on this forum for more information about this debate.
I am guessing that you are talking about 6000 amps at 120/240 volts or 120/208 volts. Can you have the utility serve the building at 480 volts, and place 480 ? 120/240 step down transformers in electric rooms, say on every other or every third floor?
As to the de-rating for underground runs, that is a subject of some debate. I would be willing to go for 15 sets of 500 MCM 75C rated copper conductors, with the parallel conduits laid out in a three vertical by five horizontal pattern, with at least 7.5 inches between any two conduits. I cannot speak for the difficulty that a team of electricians might have in installing this run. Also, I would only go for this design concept because you stated that the 6000 amps is the result of an NEC service calculation. See other discussions on this forum for more information about this debate.
Re: Service Conductors
Electrical Contractor provides the service lateral. The distance from the transformer to the main is about 75 ft. If you are going to suggest bus duct from the transformer, this is a coastal area and that type of equipment does not last long on the outside.
Electrical Contractor provides the service lateral. The distance from the transformer to the main is about 75 ft. If you are going to suggest bus duct from the transformer, this is a coastal area and that type of equipment does not last long on the outside.
Re: Service Conductors
What about multiple services? This may be large enough for the AHJ to allow that. The POCO may want to split it into more than one transformer also.
I also think 480V might be better. With 22 floors, it wouldn't take as much copper to get to the top floor. Hallway lighting could even be 277V fluorescent.
If you did have two services, you might be able to get one at 480V for equipment, and one at 208V to serve tenants.
Steve
What about multiple services? This may be large enough for the AHJ to allow that. The POCO may want to split it into more than one transformer also.
I also think 480V might be better. With 22 floors, it wouldn't take as much copper to get to the top floor. Hallway lighting could even be 277V fluorescent.
If you did have two services, you might be able to get one at 480V for equipment, and one at 208V to serve tenants.
Steve
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