Q: I’ve been reading ASTM 855, IEEE 1048 and the National Electrical Code, and I’m a little confused by the practice of grounding through a switch. Can you help me better understand this?
A: In transmission/distribution applications, there is no issue with grounding through a switch. To explain, we always have to ask whether the issue is grounding through (in the path) a switch or grounding (by way of closing) a switch. The application may sound the same, but it depends on which standard you read. Our subject matter experts think the confusion lies in the well-known NEC rules, which require permanent installations to have a connection-free path for the ground electrode conductor at the service entrance of an electrical system. According to the code, grounds – except in some specialty connections – cannot be disconnected through operation of a switch or breaker contact. ASTM 855 is an equipment manufacturer's standard that has no application to utility practices in the field other than being used as a guide for shop construction, sizing, rating and assembly of personal protective grounds. IEEE 1048 does address the value of having the grounding switches closed when de-energizing a system for work; that ground switch is a very low-resistance path to earth at the feeder or transmission bus source that will lower fault current in an accidental or inadvertent energizing of the source. The ground switch in the station is also a path to ground that will divide and help reduce the amount of induction current on a circuit. Closing the switch can help reduce induction current at a work location, depending on how far apart the work location and the ground switch are.