resqcapt19/Don—
I mean no offense, but have you found installations like that yourself? I certainly figured that would the case, and went looking for it and couldn’t find it. I looked at numerous campus-setting trailers that were shipped with their little 12-circuit pool-fence plugin-breaker panels that were prominently labeled as “100A, 120/240 volts, nominal, 3-wire ac, with grounded neutral” {article 550-4(c) style] that had a couple of roomfuls of 120v workstations and fed from staggered pairs phases on the secondary of ~75-300kVA 208Y/120V dry-type transformers.
I thought that this was to be a goose-gravy find, and would be a surefire harmonic cesspool, but I was embarrassed to tell anyone of my serious lack of discovery. There was the expected garbage on the drytype’s XO stub, and two (87 and 27 with tidy met stickers) meters and two bench-tested-by-the-leaflet-50-turn-meteod current probes showed equally pathetic neutral loading. Found out about a year later the several other hotshots independently tried it too, and of course we all read EC&M. No 3-wire trailerhouse neutral currents equaled or exceeded phase currents; there were no warm neutrals and of course, we were all p*ssed that none of our individual genius saved the day and half a million dollars worth of workstations. A leadman laughed at all of us, calling us idiots, but we knew he didn’t have a clue, and if he didn’t shut up we’d kick his butt.
Harmonics or not, there is one case where neutral conductor current will always be at least equal or exceed to the highest phase-conductor current, and that is for two-wire øø-connected are running {ie, 1ø wall-pack HVAC stuff common to trailers in this area.} They would have a tendency to swamp out—or dilute—the per-unit phase-to-neutral load current in fundamental or triplen-harmonic loads. Agreed—they would not reduce the actual current loading on the trailer “network service” neutral leads.
