The Type PJG12B relay detects grounds in a normally ungrounded field winding of a synchronous machine. It may be used for machine fields rated 600 volts or less with ceiling excitation up to 750 volts and no more than 1000 volts reverse, or back, excitation. A choice of either instantaneous or time-delayed operation is determined by selection of link position. The PJG12B oper-ates for 120 or 240 volts ac, 50 or 60 Hertz. A filter circuit reduces ripple voltage in the rectifier bridge output to no more than 3 volts peak-to-peak.

The relay is arranged for either hand-reset or electric reset from a separate switch or push button.

The PJG12B consists of a plunger-type instantaneous overcurrent relay (A), a thermal time-delay unit (T), a hinged-armature auxiliary unit (AX), and a voltage operated instantaneous unit (AY) which provides output contacts and target indication. The output contacts (AY) will make and carry 6 amperes continuously and 30 amperes for tripping duty.