Question about current being drawn by Appliances

Discussion in 'General Electronics Chat' started by niner710, Jun 11, 2009.

  1. niner710

    Thread Starter New Member

    Jan 25, 2009

    I am curious about the current being drawn by the appliances in my house. I know that the electrical outlet is 120V 60Hz and I know that different appliances will draw different amounts of current. My first question is are the electrical outlets supplying a constant 120V all the time? If so, I don't understand how different amounts of current can be drawn by different appliances. If voltage is fixed then wouldn't the amount of current being supplied be fixed as well? What is wrong with my thinking here?
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    There is an equation that explains how you can get different currents with a fixed voltage - I (current) = E (voltage)/ R (resistance). As you can see, the current can vary even with a constant voltage. So does power, which is the product of voltage and current.
  3. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    It has to do with demand. If you short out the outlet, you impose a demand back to the supply utility which will provide whatever you need. Luckily you have a series of current limiting breakers at various locations in the service and branch circuits. The current in any branch circuit follows the classic I=V/R. Turning ON appliances adds resistance (typically) in parallel, so supply voltage is seen by all devices.

    This can change however if you have an undesirable condition of series voltage drops which originate from poor connections, long run lengths, etc.
  4. Audioguru


    Dec 20, 2007
    A little incandescent night light draws only 5W. A kettle or toaster draws 1000W. A huge difference. They both use 120VAC.
  5. mbohuntr

    Senior Member

    Apr 6, 2009
    Each appliance will draw whatever current it needs to operate. The voltage is the water pressure, and current is the flow rate. 50 watts / 120volts = .41 amps. 50 watts / 100 volts = .5 amps. A light will dim, but motors will pull more current. According to Ohms law, if the resistive load remains constant, and the voltage drops, current must rise. This is known as a brown-out and damages inductive loads such as compressor motors. Utilities use protective relays to protect against undervoltage.
  6. mkbutan

    AAC Fanatic!

    Sep 30, 2008
    V=Volt's ; I=Current ; R= Resistance
    eg:- if your tv set runs on 220 v AC and let its R=100oms
    then its I (should be) 2.2A (approx.)
    i think its like that if its wrong then please rectify anybody .
  7. mkbutan

    AAC Fanatic!

    Sep 30, 2008
    In laymen language its like WATER in the TAP
    let V=Water ; R=TAP ; I=Strength of Water