Original poster: "Tim J by way of Terry Fritz <twftesla-at-qwest-dot-net>" <digital_raven45-at-hotmail-dot-com> Normally, primary to secondary arc over are RARE! I've never had one yet* But if you were concerned I would use clear polyurethane to insulate the trouble areas of the transformer. Polyurethane is a good to at least 15 kV per mil. That much I know! _