Sensing methods for a 3-phase load transfer contactor

A LOAD TRANSFER CONTACTOR is a device which connects a bank of loads to one of two power sources, herein called the normal and alternate power sources. Self-contained load transfer contactors presently employed in aircraft contain three sensing relays, each relay being connected line-to-neutral, to detect failure of the normal power source. This arrangement has the disadvantages that line-to-line faults on the normal power source may not be detected, required close tolerances on pickup and dropout voltage are difficult to maintain in an aircraft environment, and loads may be unnecessarily transferred to an alternate power source.