The ballast sets and holds the current the ultraviolet lamp arc runs at. A ballast drifting out of specification changes delivered UV-C output without failing outright, so the plant keeps running and quietly under-doses. This is the EVG55-II.3 electronic ballast. EVG is the German abbreviation for electronic ballast, so the designation names the part's function as well as its type. Confirm the designation on the existing unit before ordering — the EVG55 family has more than one revision. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.