Otter Controls Limited

Richard A Phillips

Peter W Naylor

Keith Fletcher

An electric immersion heating element dry switch-on or boil dry protector unit for an electrically heated water boiling vessel comprises primary and secondary bimetals (31,32) responsive to the heating element head temperature and each arranged for actuating a respective one of primary and secondary switching contacts (11,12) connected in the line and neutral sides of the heating element supply via respective push rods (38,44). The secondary bimetal (32) is arranged to break later than the primary bimetal (31) in a dry switch-on or boil dry situation giving rise to excessive element temperatures, and to reset before the primary in a reducing temperature situation. The secondary bimetal (32) and associated switch contacts (12) provide back-up protection in the event of failure of the primary protection on account for example of welding of the primary switch contacts (11). A neon warning lamp connected across the secondary contacts (12) will be lit only if the secondary contacts open with the primary contacts closed and thus indicates failure of the primary protection. An advantageous manually releasable latching arrangement for the primary and/or secondary switching contacts is also provided. An additional bimetal subject to heating by steam vented from the vessel operates at least one of the switch contacts when water boils in the vessel to terminate the heating operation.

Water boiling vessel immersion heater with primary and secondary thermal

A thermally-responsive electric switch has a manually-releasable latching arrangement which makes use of a latching member (6) comprising an L-shaped or bellcrank lever having an integrally formed part (11) which constitutes a release member and connects to the end of one limb (9) of the L-shaped lever via a resilient hinge portion (12). The end of the other limb (8) of the L-shaped lever constitutes a latching abutment (10) for engagement with a member (3) of the switch. The latching member (6) is so arranged that, when the switch operates, the latching abutment (10) engages with the respective member (3) of the switch so as to preclude its return and thereby latch out the switch. Resetting is achieved by depression of the release member part (11) of the latching member (6), this causing the L-shaped lever to pivot generally about the junction of its two limbs such that the latching abutment (10) moves out of its latching position and permits the switch to reset.

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Buxton, United Kingdom

Richard A Phillips