GB994436A - Thermal relay for polyphase currents - Google Patents

Abstract

994,436. Electrically-released switches. NORMACEM. Oct. 17, 1961 [Nov. 9, 1960], No. 37189/61. Heading H2B. A polyphase thermal protective device has a plurality of bi-metallic strips 1a, 1b, 1c arranged in parallel planes and having free ends engaging in a pair of slidable bars 3, 4, and a contactcarrying member 6 latched to the bar 3. The strips 1a . . . 1c are heated by the phase currents and under balanced overload conditions move both bars 3, 4 to the right until the bar 3 abuts a member 2. The movement of the bar 3 ceases and the continuing movement of the bar 4 moves the member 6 relative to the bar 3 so that the member 6 is released from a tongue 3e of the bar 3. The member 6 then moves upwardly under the bias of spring 8 to open contacts 9, 10 and close contacts 9, 11. In the event of unbalance between the phase currents, the resulting relative movement between the bars 3, 4 causes the release of the member 6 from the tongue 3e, irrespectively of the setting of the member 2. The setting of the member 2 determines only the magnitude of balanced overload currents to cause tripping, and the member 2 may be bi-metallic strip for ambient temperature compensating purposes. Resetting of the device is effected when the strips have cooled by depressing the member 6. The initial position of the strips may be adjusted by eccentric screws 13.