Mike Dolt Enterprises
Mike Dolt Enterprises
User: Guyute, Location: Ft Collins, CO
Asked on: Tuesday, March 15, 2011 at 2:58 pm EDT
Answered on: Tuesday, May 14, 2024 at 2:49 am EDT
Question: 480v line side feeding a step down 480v to 240v transformer. We are in debate on the job site whether or not the transformer or the 240v panel is the location where you bond and derive your new ground for the 240v panel. The transformer has to be bonded ground and nuetral, but the 240v panel is the first means of disconnect in the system. The question is does the nuetral and ground in the 240v panel need to be bonded, and does the new ground coming from a ufer go to the transformer or the 240v panel.
Panel Bonding and Grounding
According to the National Electrical Code (NEC), the neutral and ground wires must be bonded together at the first means of disconnect for a grounded distribution system. In this case, the 240V panel is the first means of disconnect, so the neutral and ground wires should be bonded at the panel.
Grounding Conductor Location
The NEC requires that the grounding electrode conductor (GEC) be connected to the grounding electrode system (e.g., ufer) at the service entrance or at the first system grounding point downstream from the service entrance. In this case, the 480V to 240V transformer is not considered a service entrance or a system grounding point. Therefore, the GEC should be connected to the grounding electrode system at the 240V panel.
Summary: Bond the neutral and ground wires at the 240V panel. Connect the GEC to the grounding electrode system at the 240V panel.* Bond the ground terminal of the transformer to the grounding electrode system separately. Flag for review