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Volts x Amps x Power Factor = what?

If the power we are getting at the  comp terminal block is considered "powerfactored " already , then do we have to figure in the "power factor" again when we do the V x A x PF = watts thing?


  • SWEI
    SWEI Member Posts: 7,356
    Powerfactored already?

    Not quite sure what that means, but more importantly what are you trying to calculate?  Conductor size?  OCPD size?
  • Techman
    Techman Member Posts: 2,144
    V x A x PF

    Thanks SWEI, This "thinking process" was thought up when installing a Circuit Breaker on the 24v side of a 208/240v by 24v transformer. We the consumer are paying for the electricity for our CentralAC, isn't that power at our house different than the power at the power station? And we pay for the power at the power station, not the slightly less power that we receive at home ? Is that correct? That's what I mean by PF'ed already! If I make sense! LOL
  • NYplumber
    NYplumber Member Posts: 503

    Yep Techman, good question.

    When sizing fuses for DC, its VxA=W.

    For AC its VxAxPF=W.

    If we are looking for the fuse/breaker size for an appliance, you can use standard 125v or any numerical value you deem proper and place the appliance watts in the equasion VxAxPF=W if you are unsure what the actual voltage is.

    What Techman is asking is, if you test your wall outlet and get 119vac, why do you still use the power factor in the equation? That is like taking the "efficiency" factor and using it twice.
  • Techman
    Techman Member Posts: 2,144

    Yeah, KindaSorta like NYp said, I think
  • SWEI
    SWEI Member Posts: 7,356
    Your electric meter

    reads true wattage, and properly accounts for power factor.

    The separate demand load (kVA) and reactive load (kVAR) charges on a commercial account cover the utility's butt if you are doing bad things to the grid.
  • ChrisJ
    ChrisJ Member Posts: 15,170
    edited June 2014
    VA vs Watts

    I'm a bit confused by this thread.

    The reason VA is different from watts is because some loads, such as an inductive motor will cause the current draw to be out of phase with the voltage.

    In most places, you pay for wattage not VA so a poor power factor won't cost you a dime, you're still paying for real power, not apparent power.

    When sizing a breaker, fuse or conductor I would think you go by current consumption alone, not volt-amps or watts?

    I'm posting because I want to make sure my understanding is correct. If it is not, please let me know.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • SWEI
    SWEI Member Posts: 7,356
    Correct on all counts

    Power companies meter kVA and kVAR on medium to large commercial and industrial accounts.