Otter Controls Limited

Arthur M Blackburn

Robert Andrew O'Neill

Terence J Foster

Ian G White

An element protector control for protecting the electrically powered heating element of a kettle against overheating has primary and secondary (or back-up) modes of operation. The primary protection mode utilizes a dished, snap-acting bimetal which is oriented so that the side of the bimetal which is convex when the blade is cold faces the heating element head, and the bimetal is sprung against a flat rear surface of the element head so that the bimetal in its cold condition flattens against the element head. The bimetal determines the condition of a pair of switching contacts provided in the control. The bimetal is mounted in a carrier which is spring biassed towards the element head and, for providing the secondary protection mode, the carrier is formed of a thermoplastics material so that in the event of failure of the primary protection in an overtemperature situation so that the element temperature continues to rise, the carrier will collapse towards the element head, and the collapse of the carrier is arranged to disconnect the control from its power supply terminals.

Thermal control units

An overload protection switch for an electric motor comprises a bimetallic switch-actuating element carrying a moving contact of the switch, a first terminal part having an extension which defines a mounting for the bimetal, and a second terminal part having an extension which mounts a fixed contact of the switch, the first and second terminal parts being received in a moulded plastics switch body portion. In contrast to prior art switches of this type where the terminal parts were manufactured of material having a low electrical resistance, the invention manufactures these parts of high resistance material selected such that under very high overload current levels the resistance heating in the terminal parts does not significantly determine the switching characteristics of the switch on account of the overwhelmingly predominant bimetallic heating, but towards the other end of the overload current scale the self-heating of the terminal parts significantly affects the switch operation.

Electric motor protection switches

A snap-acting thermally-responsive actuator for an electric switch comprises a pear-shaped dished bimetallic blade having a U-shaped cut-out defining a tongue extending from its root or attached end at the larger end of the pear-shaped blade axially of the blade towards the smaller end of the blade, the tongue extending between outer leg portions of the blade which each have a width which decreases in a direction from the larger towards the smaller end of the blade. When the blade is mounted in a switch with the tip end of its tongue secured to a terminal part of the switch and with a moving switch contact carried on the smaller end of the blade for co-operation with a fixed switch contact secured to another terminal part of the switch, the blade thereby being susceptible to heating by electric current flow through the switch when the switch contacts are closed, the pear-shaped blade configuration coupled with the thinning of the outer legs towards the smaller end of the blade provides improved mechanical switching characteristics and improved self-heating characteristics in the blade leading to improved consistency of operation.

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Buxton, United Kingdom

Arthur M Blackburn