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How to read electric bill to calculate Usage - Sample provided

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    How to read electric bill to calculate Usage - Sample provided

    I've attached a sample electric bill for one month (have 12 months total of usage)


    I'm trying to determine the current usage because the owner is adding lots of new load and I want to be able to determine existing capacity vs. new required capacity.


    Do I just take where it says Demand-kW and that's how much consumption the user has? Or do I do something with the kWh row?

    Click image for larger version

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    Better pic here: https://cdn1.imggmi.com/uploads/2019...a5222-full.png

    Thank you!

    #2
    You cannot determine service capacity from a utility bill. From their standpoint, 63,588kWH could be 1kW for an hour, followed by 63,587kW for an hour, with nothing else all month, it all looks the same at the end of the month.

    The kW and kVA demand values are just the peak amount used during sliding time slot called the "demand window", but they don't say here whether it is 15 min., 20 min,. or 30 min., all of which are common in different areas. But again, that is the AVERAGE across a single demand window, it means nothing with regard to what they have available.

    Can't you just ask the utility for the size of the service?
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

    I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

    Comment


      #3
      Originally posted by Jraef View Post
      You cannot determine service capacity from a utility bill. From their standpoint, 63,588kWH could be 1kW for an hour, followed by 63,587kW for an hour, with nothing else all month, it all looks the same at the end of the month.

      The kW and kVA demand values are just the peak amount used during sliding time slot called the "demand window", but they don't say here whether it is 15 min., 20 min,. or 30 min., all of which are common in different areas. But again, that is the AVERAGE across a single demand window, it means nothing with regard to what they have available.

      Can't you just ask the utility for the size of the service?
      Thanks Jraef. I'm basically trying to determine the margin (available capacity still left) in the existing system and how much more it can handle.

      I can figure out how big their existing service is. Let's say it is 480V/3Ph, 200A, well I know I'm using 138A (per the demand-kw on the electric bill) and I would have another 62A available. Or I would need to upsize the service.



      The NEC allows this method right?

      Comment


        #4
        Originally posted by Designer69 View Post
        The NEC allows this method right?


        Not that I am aware, see 220.87

        looks like the maximum demand here might be 127.6 kVA, but it isn't clear to me if that is for the past month for past year. assuming it is for the year, multiply by 1.25 per 220.87 then add the new continuous and non-continuous loads. that will determine your minimum feeder size for the new installation.

        Last edited by drktmplr12; 07-16-19, 05:19 PM. Reason: removed quote

        Comment


          #5
          I think if you can verify that the utility bill is based on 15 minute interval data then you can use that to comply with 220.87. Regardless of code, it might be a good idea to get a years worth of utility bills and use the highest value.

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