The purpose of this device is to allow a path for the UPS protected equipment to be fed by utility power in the event of UPS service or replacement. Make-Before-Break Maintenance Bypass Switches As you would expect, if the two waveforms were coincidental (peaked at the same time), you would add both 120V peaks together to get 240V. When one waveform is at its peak, measuring 120V, the other is only part of way through its cycle, measuring only 88V. Since the two waveforms peak at different times, the combined power you get from them is less than the numerical sum of the two. When using 120/208V single phase, you will use any two of those same three hot conductors, with the two waveforms peaking 120 degrees apart from each other. If viewed on an oscilloscope, the three voltage waveforms on the three “hot” conductors all peak at different times: each one is 120 degrees behind the next. This all stems from the nature of 208V power and how it is affected by transformers.ġ20/208V single phase is derived from 208V three phase power. Simply put, on some combinations of UPS model, bypass switch type, and input voltage, there exists the potential for an incompatibility. SEPS has configured the standard part numbers to avoid potential issues, but some questions often remain. This is one of the subjects that raise the most questions because it is different for the different UPS types, it is something you may not encounter on every project, and it has the potential to be a costly error if ignored.Īs I said, this situation is not an issue in every case. If you are designing a site that will have 208V single phase power to feed the UPS, you should be aware of the nature of 208V power and how it works with different UPS models.
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