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.