Mike Dolt Enterprises
Mike Dolt Enterprises
User: Guyute, Location: Ft Collins, CO
Asked on: Wednesday, April 13, 2011 at 6:44 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:09 am EDT
Question: I have a 400 amp service with a 400amp em disconnect for the genset with an ATS. There is no breaker on the genset, and the neutral is bonded at the genset. Do I bond and ground the 400amp em disconnect to the ufer, water, etc or is the ground rod and ufer at the genset suffiecient for my main bond. My big confusion is if in a back up power situation doesn't the 400 amp em disconnect become the main means of disconnect and a seperately derived system. If this is the case then I would need to have my main bonding electrode at the em disconnect sized according to 250.66. I also have to have an equipment bond between the generator and the disconnect. Any thoughts.
Main Bonding Electrode Location
When the generator is the primary source of power (during a blackout), the 400 amp EM disconnect becomes the main service disconnecting means. Therefore, the main bonding electrode must be located at the EM disconnect. This is because: The EM disconnect is where the neutral and ground are bonded in the backup power scenario. The main bonding electrode connects the neutral and grounding system at the service entrance.
Sizing of Main Bonding Electrode
According to NEC 250.66, the main bonding electrode must be sized based on the available fault current at the service entrance. In this case, the 400 amp EM disconnect would be supplying the entire electrical system. Therefore, the electrode must be sized accordingly.
Equipment Bonding Jumper
An equipment bonding jumper must be installed between the generator and the EM disconnect. This jumper connects the ground bus in the generator to the ground bus in the EM disconnect. This ensures that all electrical equipment connected downstream of the EM disconnect has a proper grounding path.
Ground Rods and Ufer
The ground rods and Ufer at the generator location provide the grounding for the generator frame and neutral bonding. However, these grounding electrodes are not sufficient for the main bonding electrode at the EM disconnect. This is because the EM disconnect is where the neutral and ground are bonded for the entire electrical system.
Conclusion The 400 amp EM disconnect must be bonded and grounded at the location of the service entrance. The main bonding electrode at the EM disconnect must be sized according to the available fault current. An equipment bonding jumper must be installed between the generator and the EM disconnect. The ground rods and Ufer at the generator location are not sufficient for the main bonding electrode. Flag for review