Scott35's transformer pictures spark the memory of one version of utility-supplied three-wire delta service I found at a pretzel plant in El Segundo, CA {north of Disneyland ~15 miles.} The building had an original 800A 240V 3ø 3-wire corner-grounded-delta service, with several drytype 1ø transformers for 120/240V 1ø 3-wire feeding lighting and 120V convenience outlets. More recently, a 400A 120/240V 1ø 3-wire service had been added. The plant’s maintenance crew did onsite electrical troubleshooting, and some were very confused by the two different grounded-circuit conductors {all correctly white} that had completely different voltage relationships. In many places in the plant, they found circuits with 240V to ground, and in other places 120V to ground, but with no distinct phase/color-coding or markings to readily differentiate the different systems.
At the end of two weeks of training to understand their electrical system and work on it safely, out of a crew of about 8, a couple of guys understood it and were committed to teach others what to expect, and why the plant has more that one set “neutral” conductors. In corner-grounded-delta circuits the “white wires”/grounded-circuit conductors were not neutrals by Code definition, but “white wires”/grounded-circuit conductors in 120/240V circuits are. To complicate matters even more, the corner-grounded 3ø system used some 2-pole fusible switches, and both two- AND three-pole circuit breakers.
[The plant’s 1ø and 3ø transformers were served by once regionally popular 4800V 3ø ungrounded-delta distribution.]
[This message has been edited by Bjarney (edited 02-21-2004).]
