| 摘要 |
An automatic changeover switch 104 has a first state in which a first load 103 is directly connected to a supply 101 and a second load 102 is connected to the supply via a current limiting resistor R1, and in response to a demand for current by the second load 102, the switch 104 switches to a second state in which the first load 103 is disconnected and the second load 102 is supplied via a bypass around the resistor R1. The arrangement may be used in a caravan or chalet with a limited supply, the first load 103 being a low priority appliance, such as a heating or cooling appliance, and the second load 102 being a higher priority appliance such as a kettle or microwave oven. The resistor R1 allows sufficient current flow to power a clock of the microwave oven. An override switch (S2, Fig.3) may be provided to turn on the second load, and this switch may be operated manually or by a thermostat or a timer clock. Demand for current in the second circuit 102 may be detected by a current transformer 106. Alternatively, demand for current by the second circuit 102 may be detected from the voltage drop across the current limiting resistor (20, Fig.4) resulting in drop-out of a relay (4) and thereby of a relay (5) which effects the load circuit changeover. When a current transformer (22) senses a fall in the current demand from the second load, another relay (6) resets relays (4, 5) to reconnect the first load.
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