Thermal overload relay having a N.O. or N.C. contact unit select

Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated

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335198, 337151, H01H 7120, H01H 7322

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active

043921183

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. auxiliary contact units (57) are assembled from common parts plus a selected one of two interchangeable contact bias springs (74, 78) and are constructed so as to have wiping action to insure low voltage level reliability.

REFERENCES:
patent: 3478292 (1969-11-01), Carter et al.
patent: 3890585 (1975-06-01), Hartop
Square D Co. Service Bulletin 277AS, Classes 8502 and 8536, Size O-AC, Magnetic Contactors and Starters Type SB, Series A or Series B, Jul. 1975, pp. 1-2.

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