Abstract: An amplifying circuit includes a low gain amplifier having positive and negative inputs and an output. A high impedance path provided by, for example, a low gain unity buffer amplifier feeds from the negative input to the output of the amplifier a first voltage (KV.sup.+) equal to a second voltage (V.sup.+) at the positive input of the amplifier multiplied by the reciprocal of the open loop gain (A.sub.OL) of the amplifier. This circuit simulates a unity gain buffer amplifier having a high input impedance and a high open loop gain using a low open loop gain amplifier and a feed forward arrangement. The use of a low gain amplifier avoids the need for large area transistors and the resultant large parasitic capacitances and so facilitates high speed operation.

Abstract: A thermal overload relay for a three-phase power supply circuit having an auxiliary normally open (N.O.) or a normally closed (N.C.) contact unit (FIG. 5, FIG. 6) selectively addable in the field. The relay is provided with the standard normally closed contact by way of a subassembly (20) that is installed by the manufacturer for circuit protective purposes and a slot (12p) and securing means (12n, 77) alongside this subassembly for receiving an auxiliary contact unit (57) that can be inserted and secured by a screw (77) in the field. A contact operating lever (54) is constructed so that it will actuate the auxiliary contact unit (57) at the end of the trip stroke thereby affording redistribution or retiming of the spring forces that will enhance the tripping function because less initial spring force is required at the beginning of the trip stroke. The N.O. and N.C.