More about standby generator grounding, GFP, and currents that go bump in the night

The issue of generator grounding, separately derived systems, and the application of 3-pole and 1-pole transfer switches continues to be misunderstood and misapplied by design engineers in spite of several IEEE papers on the subject. Incorrect generator grounding and/or incorrect transfer switch selection can result in noncode complying installations, intermingling of ground and neutral currents, and possible incorrect ground-fault sensing. In order to properly ground multiple service and multiple generator installations, the electrical design engineer must have an in-depth understanding of all of the variables involved. The purpose of this paper is to look at a variety of systems utilizing multiple services, multiple generators, and multiple transfer switches, and analyze ground and neutral currents in terms of their effect on system safety and reliability. This paper examines configurations that are known to violate the National Electrical Code (NEC), and it examines possible problems with systems known to comply with the NEC. The paper addresses new systems as well as existing systems that are candidates for possible retrofit.