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current flow in ac cirtuits

Discussion in 'General DIY' started by AnonymousImport, 22 Sep 2002.

  1. AnonymousImport

    AnonymousImport

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    an electrician friend believes that it is possible for current flow to increase in an ac circuit when voltage is reduced

    surely this cant be corrrect!!?

    we were discussing the installation of a shower unit and he stated that if the mains voltage were to drop to say 220v then the currnt would increase and therefore any fuse or wire would need to be rated higher to take account of this

    would be grateful for your opinion
     
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  3. AnonymousImport

    AnonymousImport

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    Spot on, I'm afraid.

    You can work out the current by using this equation:

    Current = Power divided by Voltage

    Where Power is the rated power of the shower (in Watts)

    Example:
    A 8KW shower (8000 watts)

    At 240V the current = 33.33 Amps
    At 220V the current = 36.36 Amps

    Hope this helps

     
  4. AnonymousImport

    AnonymousImport

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    Actually, while the above formula is correct, it's not quite that simple. A shower rated at 8kW will only produce 8 kW of heat when it is getting its rated voltage, usually 240V. If there was only 220 V at the shower terminals, then it would produce less than 8 kW. The two determining factors are the resistance of the heating element, and the voltage across it. Unfortunately, the resistance of the element changes with temperature, so you begin to see why it is not easy to predict the exact current at supply voltages other than the rated voltage.
     
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