220V to 208V Buck-Boost Transformer — Step-down, Single Phase
See how a 220V to 208V single phase buck-boost transformer corrects voltage and how to select the proper model.
Choosing a 220V to 208V transformer
ANSI C84.1 puts the upper limit of Range A service voltage for a 208 volt system at 218 volts. A reading of 220 is past it, at the edge of the wider Range B, and every 208 volt load in the building is running roughly 6 percent above nameplate. A 220V to 208V buck-boost transformer removes that surplus with a fixed 5.5 percent buck. The pair applies to genuine 220 volt supplies and, more often, to nominal 208 volt services that simply measure 220 at the panel. Single-phase and three-phase, 10 through 60 amps.
A 208 volt system reading 220 is usually the result of a supply with more capacity than the building needs.Utility transformers and their tap settings are chosen for worst-case load at the end of a feeder. A tenant space near the substation, or a building whose connected load never approached the service it was designed with, receives voltage at the top of the band all day. Interior dry-type transformers left on a raised tap after a load change do the same thing.Two modern causes are worth checking. Facilities with significant on-site solar often see voltage rise during export hours, which is when the reading tends to peak. And spaces built out for heavy equipment that was never installed, or that has since been replaced by lower-draw machines, carry an oversized service against a light load.The equipment that objects is the 208 volt rated kind: elevator and escalator controllers, LED drivers and lighting ballasts, rack PDUs and UPS units, commercial kitchen equipment, packaged HVAC, and any 208 volt heating element.