1200A svc main bonding jumper

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Ken Kotrady

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We have an existing 2400A 480V 3 section main switchboard in an inside electric room. We have an engineered drawing from a local electrical engineer that did not address this issue. Our scope of work is to down size the main service to 1200A, tap the FPL primary feeders, penetrate the outside wall and add a 1200A 3ph NEMA 3R service rated main ATS, disconnect the jumpers in the switchboard from the FPL primary to the second and third section of the switchboard and refeed those sections from the load side of the ATS. The plan called for the raceway from the existing FPL side of the switchboard to the new ATS with PVC to avoid any bonding requirements on the primary side. We could not do it in PVC because of allignment problems and working space, we were forced to install (3) 4" pieces of sealtight 5 ft long with (4) 600MCM conductors in each. We installed bonding bushings on the primary side of the cabinet and bonded them together with (1) 3/0 conductor per table 250.66. The local inspector would not accept this 3/0 bonding jumer and requested it to be redone in 250MCM. Stating NEC 250.28 (D) Sizing of main bonding jumpers His comment is the total of the supply conductors are larger than 100 KCML the bonding jumpers shall have an area that is not less than 12 1/2% of the area of the largest phase conductor. I told him that the size of the supply conductors are not to be added together, they are to be the actual size and the 3/0 bonding jumper is correct. He would not accept it. The engineer of record is on vacation for 3 weeks and I cannot get a reply from him. If this inspector is correct I would have to schedule another shut down of the facility and rework the feeders and change out what we did. The facility will not pay the invoice until a final inspection is approved. The inspector I have mentioned is the chief electrical inspector. He told me if I could prove him wrong he would sign off. Help
 
Ken Kotrady said:
. The local inspector would not accept this 3/0 bonding jumer and requested it to be redone in 250MCM. Stating NEC 250.28 (D) Sizing of main bonding jumpers His comment is the total of the supply conductors are larger than 100 KCML the bonding jumpers shall have an area that is not less than 12 1/2% of the area of the largest phase conductor. I told him that the size of the supply conductors are not to be added together, they are to be the actual size and the 3/0 bonding jumper is correct. He would not accept it.
I think he is correct. Read 250.24 1&2.
 
Ken Kotrady said:
We have an existing 2400A 480V 3 section main switchboard in an inside electric room. We have an engineered drawing from a local electrical engineer that did not address this issue. Our scope of work is to down size the main service to 1200A, tap the FPL primary feeders, penetrate the outside wall and add a 1200A 3ph NEMA 3R service rated main ATS, disconnect the jumpers in the switchboard from the FPL primary to the second and third section of the switchboard and refeed those sections from the load side of the ATS.
It sounds like you have installed an ATS to serve sections 2 and 3. I assume section one is connected to the FPL service with a 1200 amp main. If the ATS is connected directly to the FPL service, where is the main breaker that feeds 2 & 3?
 
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