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. Match the ballast to the lamp rating actually installed rather than to the reactor model alone. This is the ballast for the A15. The matching quartz module is stocked under item 13136-1110. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.