size breakers for 3-phase UPS

Discussion in 'General Electronics Chat' started by OuuuChhh, Mar 2, 2011.

  1. OuuuChhh

    Thread Starter New Member

    Mar 2, 2011
    2
    0
    Hi, I need to estimate the breaker amps for 2 3-phase UPS. The output is 140KVA y 60KVA L-L 208V. How can I estimate this?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,783
    943
    If there is no mistakes in your numbers the current will be very much in excess of 150 amps.

    You will require special breakers to handle this level of power. They are not something you can buy at the individual consumer level. A commercial power company equipment provider would be a better place to seek information.
     
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    if your looking for overcurrent protection on the input, you must go by nameplate data, and it could be just about anything.

    On the output side, you are not protecting the source, but rather the load and it's associated wiring. The load will determine the required current draw and subsequently the wire size. You will then protect that wire with an overcurrent device, unless guided by load characteristics. One thing that your source will tell you is the short circuit current, which your interrupt ratings must take into consideration. If your UPS is driving into a transformer, then the transformer circuit has code requirements. Primary and/or Secondary overcurrent is required at 125%, and the code dictates which is required. Breakers are not necessarily special, just expensive.
     
    Last edited: Mar 2, 2011
  4. OuuuChhh

    Thread Starter New Member

    Mar 2, 2011
    2
    0
    the specifications require an outside bypass for the UPS, that's what I'm trying to estimate, so I need 3 "breakers" on that panel in case the UPS need to be retired for reparation
    (sry my English I'm a Spanish speaker)
     
  5. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    maybe your looking for isolation switches or disconnects? If it's breakers you want, they need to be sized according to the load and branch circuit. I don't know your local codes, but NEC and CEC have requirements for transfer and isolation switches.
     
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