| 摘要 |
An electrical water heater 220 connectable to a mains power supply includes a heater element 222, a switch (see Fig 3 for an example of a relay switch) for the heater element that forms part of the water heater, and a switch controller 224 to control the switch. The switch is located downstream of the controller so that the switching off of power to the heater element will not interrupt the supply of power to the controller. The switch controller serves to control the switch to make power available to the heater element with the switching of the switch being controllable to occur with a delay within a time window in relation to an initial switching signal. For example, the controller may be programmed to only switch power to the heater during the lowest tariff period, but if the tariff periods vary with the load experienced by the utility, and in particular shift to a higher tariff for a short period of time, the controller exercises a guard delay time to ensure that most of the time the heater will only be turned on when the tariff has dropped to the lowest value.
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