Abstract: An apparatus for performing a dual mode supervisory operation, according to whether the self limiting cable is "OFF" or "ON". When the self limiting cable is in the "OFF" mode, a solid state device compares a known resistance value of the self limiting cable over its entire length by alternately testing from each end of the cable. The values of fixed comparator resistors are set at a specified ambient temperature depending on the length of the cable. Both high resistance and low resistance samples are compared to determine whether a short or an open exists over the expected operating range. When the self limiting cable is in the "ON" mode, an AC transfer relay switches the solid state supervisory circuit to a Dummy Load. This relay simultaneously switches high voltage to the self limiting cable and a self limiting cable "ON" lamp is lit. A solid state supervisory/override relay prevents false failure signals during ON-OFF switching times.