Starting switch for motor driven hand tools - has three sets of contacts, one controlled by time delay element to by=pass starting current limiter

摘要

The starting switch for electric hand tools comprises three contact sets (2, 3, 4) which are mechanically coupled (5). Mains supply is connected to the first two sets of contacts. In parallel with the third switch is a current-limiting stage (7). In series with this is a delay mechanism such as a bi-metallic strip (8). This operates a latch (9) on the third contact. When the start button is operated, the first two contacts are closed, the third being held open by the latch. The starting current for the motor is limited by the current-limiter. Current also flows through the bi-metal element and after the delay time has elapsed, this then operates to release the latch on the third contact. The motor is then connected directly to the mains supply.