Voltcraft 3 phase socket tester voltcraft st 16b the voltcraft st 16b socket tester is intended solely for a quick diagnosis of cee power current sockets on the public alternating current grid max 415vac which are secured with a 16a fuse it does not replace the correct testing by a specialist this device recognises interruptions to the three phases the neutral wire or the earth additionally the rotating field clockwiseanticlockwise is displayed voltcraft st 16b 3 phase socket te