Abstract: A transient voltage surge suppressor is provided to protect equipment with voltage sensitive electronics, such as office equipment, from surges or transients in the multi-phase power distribution network furnishing power. The surge suppressor senses the incoming voltage and electrically disconnects its output to the office equipment if a voltage surge above an established level is sensed. The suppressor also disconnects its output when a ground connection in the multi-phase power network is disconnected to protect the equipment against excessive voltages. In this situation, the suppressor circuit protects its internal components from damage and possible fire hazard when its output is disabled, so that the suppressor can resume its function when conditions in the power distribution network return to a satisfactory state.

Abstract: An improved power filter circuit is disclosed. The improvement concern providing a clamping device between a ground lead and a terminal of a safety circuit such that when the power filter has its hot and neutral leads properly connected to hot and neutral leads of a utility circuit, a switch of the safety circuit connects the clamping device to be between ground and neutral leads of the power filter circuit, but when the hot and neutral leads of a utility circuit are reversed, the switch of the safety circuit connects the safety circuit directly between the neutral and hot leads of the power filter circuit, thereby creating an indicator, such as a red light, that the hot and neutral leads are reversed, yet the clamping device is now not connected between the neutral and ground leads of the power filter circuit. Accordingly, the clamping device connected between the ground and neutral leads may be rated during normal operations at a lower value, e.g.