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  1. #1
    Join Date
    Jun 2003
    Location
    UK
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    6,601

    kWh for 20 Amps @ 208V

    I'm having a Monday morning here. Just want a double check

    If we have a rack at pulling 20 Amps @ 208V for 30 days how many kWH is that.

    I've got it as

    20*208 = 4160 watts = 4.16 kW

    720 Hours gives 2995 kWh

    If we are charged $0.10 per kWh (just for example here its not a real number)

    That means we would have a bill of ~$299.50/mo for power?
    Russ Foster - Industry Curmudgeon

  2. #2
    Join Date
    Jan 2010
    Posts
    652
    If it is actually pulling 20 amps, approximately yes.
    You would need a 30 amp breaker and 30 amp pdu to actually pull 20 amps
    The utility may also have kW demand charges, and taxes, and etc etc.

    Also, this doesn't account for the UPS overheads. Some data centers use a rule of thumb of doubling the raw utility power costs to cover the UPS, generator, power distribution, etc

  3. #3
    The correct formula is
    (volts x amps x power factor x phase x rated breaker)divided by 1,000

    So it depends on the phase and rated breaker. The industry standard is 80% use of the rated breaker.

    1 phase
    208 x 20 x 1 x 1 x .80 / 1,000 = 3.328kw

    3 phase
    208 x 20 x 1 x square root of 3 x .80 /1,000 = 5.76kw

  4. #4
    Join Date
    Feb 2002
    Location
    New York, NY
    Posts
    4,612
    Your math is good, but keep in mind that for a 20A circuit, your continuous usage should not exceed 16A, so your bill should be lower.
    Scott Burns, President
    BQ Internet Corporation
    Remote Rsync and FTP backup solutions
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  5. #5
    Join Date
    Sep 2010
    Location
    Dallas, TX
    Posts
    215
    Don't forget that the electricity usage will create heat, and thus, you will spend money to cool it as well.

  6. #6
    Join Date
    Nov 2009
    Location
    Reston
    Posts
    305
    Cooling uses about 25% of actual power consumption. So, for every 10KW your environment is using, plan on using an additional 2.5KW for cooling. Of course this is 100% accurate and would depend on what systems you have in place / how efficient, and also ventilation - but if you are starting from scratch, hopefully this should give you some idea of what to expect.
    Dan Buyer
    InfoRelay - Connected, Protected, Perfected.
    Equinix LAX & DC, One Wilshire, Wilshire Annex, MPT, VE, 1275K, Reston Exchange, Reston Equinix, 60 Hudson, NYC, and Chicago
    www.inforelay.com

  7. #7
    Join Date
    Jan 2011
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    rules.php
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    Cooling uses about 25% of actual power consumption. So, for every 10KW your environment is using, plan on using an additional 2.5KW for cooling. Of course this is 100% accurate and would depend on what systems you have in place / how efficient, and also ventilation - but if you are starting from scratch, hopefully this should give you some idea of what to expect.

  8. #8
    Join Date
    Jan 2003
    Location
    Chicago, IL
    Posts
    6,889
    Quote Originally Posted by dbuyer0 View Post
    Cooling uses about 25% of actual power consumption. So, for every 10KW your environment is using, plan on using an additional 2.5KW for cooling. Of course this is 100% accurate and would depend on what systems you have in place / how efficient, and also ventilation - but if you are starting from scratch, hopefully this should give you some idea of what to expect.
    Then you're looking at another ~25% for loss at the distribution layer, UPS overhead, etc.
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