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Thread: Existing generator running building based on 702.4(B)

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    Existing generator running building based on 702.4(B)

    Can an existing 900kw standby generator be wired to take the load of an entire building if the highest actual recorded load was say 678kw? Ideal case to maximize the usage of a lightly loaded genset. It looks like code will let you, but it just seems to simple for me.
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    Why would it not be okay?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    Quote Originally Posted by LarryFine View Post
    Why would it not be okay?


    Just seems to easy.

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    I remember some points from my generator classes: 1. depend on characteristic of generator, some of generators can be loaded 50%-85% initially, after few seconds you can load it to 100%. 2. in order to start motor(s) you generator size should be at least 3 times bigger than motors you want to start, this number depend on specific model number. 3. if the generator is cold it can not be loaded 100% until it reach his working temperature.

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    Quote Originally Posted by victor.cherkashi View Post
    I remember some points from my generator classes:

    1. depend on characteristic of generator, some of generators can be loaded 50%-85% initially, after few seconds you can load it to 100%.

    3. if the generator is cold it can not be loaded 100% until it reach his working temperature.
    Never heard of this- is it true?

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    of course it is true to certain degree, depend on loads types. if generator serves office building with little motors, you don't have a problem. if the generator have to start a lot of motors, the voltage and frequency goes down. how much they will go down all depends what is strat current of loads, internal resistance of generator, rotor type. is it a problem temporary voltage and frequency reduction for your building? what is treshold of voltage and frequency in generator controller? I was told by my teacher that these questions have to be answered if you want to make sure your generator will work in worst case scenario.

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    Quote Originally Posted by victor.cherkashi View Post
    of course it is true to certain degree, depend on loads types. if generator serves office building with little motors, you don't have a problem. if the generator have to start a lot of motors, the voltage and frequency goes down. how much they will go down all depends what is strat current of loads, internal resistance of generator, rotor type. is it a problem temporary voltage and frequency reduction for your building? what is treshold of voltage and frequency in generator controller? I was told by my teacher that these questions have to be answered if you want to make sure your generator will work in worst case scenario.

    Sent from my ONEPLUS A6013 using Tapatalk


    You are right about the motors and voltage dip, but never heard it pertain to lighting loads. Ie a 500kw genset can take 500kw of fluorescent or Tungsten load within a few seconds of coming up to speed.

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