On Sun, Jun 26, 2011 at 05:27:10AM -0700, Leo Bicknell wrote:
It's not that you couldn't install a closed transition ATS in the ATS 1a/1b location from an electrical point of view, but I don't think codes, power companies, or common sense make it a good idea. As others have pointed out, the grid can do weird things because your neighbors did something stupid, or a car hit a power pole and shorted 3 phases together. Syncing to it is, well, crazy.
It makes little sense to sync to the grid when the generator is only used when the grid is down - and unless you run your generators 24/7 your UPS will have to make up for the comparatively long time it takes for the generator to start, so it's rather useless to sync the generator when the power comes back so you can avoid a sub-second break when transferring back to utility power. UPS's shouldn't mind a break-before-make transfer, and motor loads are more and more often inverter/VFD driven types that should have their own delayed start logic that will hopefully handle most power glitches gracefully. Power distribution downstream of UPSs is a different animal with different goals, and there synchronized UPSs and make-before-break makes sense. To at least pretend to be relevant, the absolute frequency of the grid is, again, not relevant at all - and when the power is out, you won't be able to sync to it anyway.