Multiple hook ups

Discussion in 'General Electronics Chat' started by PhiDor, Jan 4, 2011.

  1. PhiDor

    Thread Starter New Member

    Dec 24, 2010

    I have always had a problem understanding electricity. I have what to some may be a simple question.

    Suppose an AC circuit with 120 volts and 20 amps. If I plug an extension cord into that circuit and assuming it's of sufficient size to adequately carry the load, how many other cords can I plug in to that line? How do multiple cords affect the amperage? voltage? Is there a formula for this? And I guess the length of the cords comes into play here also.

    Now if someone can answer that in easy to understand terms, I would appreciate it very much.

    Thank you.
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    It is a simple question, but it is not simple to answer. The answer is that you can draw up to 20 amps, but the current draw is a combination of the current requirements of the devices connected to the circuit plus the losses in the extension cords. The losses in the extension cords depend on the length of the cords and the gauge of the wire in the cords. The smaller the gauge, the greater the losses, and smaller gauge wires are indicated by larger numbers.
  3. Hagen

    Active Member

    May 8, 2010
    OK well lets say you have a 120 volt receptacle to plug into, and lets say it is supplied from a 20 amp breaker back in your panel. That means that there is 120 volts ready to supply whatever load you plug into that receptacle, but keep in mind that the devices you plug into that receptacle are what determine how many amps will flow. The number of cords being supplied by that receptacle is kind of irrelevent. The cords by themselves don't cause any amps to flow. You could power about 20 100 watt lightbulbs at about one amp each, or one air compressor motor that draws about 20 amps. If the total load exceeds 20 amps, the breaker will eventually trip off. Does this make any sense to you?
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
    You can try to think of cords as resistors, the more cords you have, the more resistors in series you have. Resistors in series add up directly, so the more cords you have, the bigger resistor you have.
  5. someonesdad

    Senior Member

    Jul 7, 2009
    Another analogy is the water faucet. You can only get so much flow from a given water faucet. Connect multiple hoses and their summed flow will be the total flow of the faucet. Each of the hoses/joints/fittings will also have frictional losses, analogous to the ohmic losses of the extension cords.
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    I'm not current with the NEA, but the limit for steady draw in 20 amp circuits used to be 16 amps.
  7. #12


    Nov 30, 2010
    80% is the "design Limit" rule for electricians, but I've long wondered how the NEA prevents consumers from using 19 or 20 amps from a circuit with a 20 amp circuit breaker. Things that make you go Hmmm...
  8. PhiDor

    Thread Starter New Member

    Dec 24, 2010
    Thanks to all who replied to my posting. You did explain a lot to me.

    The original problem was this. I belong to an Airstream Travel Trailer Club. (WBCCI) We have rallies at which we sometimes have what is called "Rally Electric". If we're parked in a field with only a few electrical outlets, we may be told that we only have 3 amp electric. I always wondered how the amperage was divided up among us. We might have three trailers on a circuit (there are the multiple cords) or we might have 10 on a circuit. Invariably, someone will use their hair dryer, microwave, and so on all at once and trip the breaker. Then everyone else starts going nuts. So I guess when they say it's 3 amp electric, it's just a way of saying be careful of what you run and be considerate of your fellow campers. If no one uses any appliances, one person could use 20 amps no problem, Right? Or two people could use 10 amps each, etc.

    Thanks again. :D
  9. #12


    Nov 30, 2010
    You got it.

    You can plug in a hundred cords, but if nobody uses any power, there is no amperage.