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  1. GenSwgrEng

    In-Rack Transfer Switch

    Is anyone aware of a transfer switch intended for use in an IT server rack? Rating would be 30-50A, and would need to be able to transfer in anywhere from 45ms to 45s. Can you recommend a manufacturer, or better yet provide a guideform spec? It seems to me that UL1008, emergency-system rated...
  2. GenSwgrEng

    Why AC Power Distribution in Data Centers

    For a long time, I've wondered why data centers don't use DC distribution instead of AC. After all, it takes a lot to bring in AC power from the drip, rectify it to DC for the UPS batteries, invert it back to AC, synchronize AC outputs from multiple UPSs, and distribute AC power to the...
  3. GenSwgrEng

    Relay Protection

    Yes, it was proper operation of the breaker to trip on 51N. You don't want to single-phase your loads. No, it is not ideal to have all 5 circuits dropped to clear a problem on 1. Ideally you would have a breaker, or at least a switch that could open to clear the fault as locally as possible...
  4. GenSwgrEng

    Masterpact NW Breaker Trip Unit Reading Current High

    I'm inclined to believe you had a bad connection on the trip unit's sensor plug. It may be that the connection was "fixed" in the process of removing and re-installing the breaker. With the breaker out of service, I would remove, inspect/clean and replace the sensor plug and re-test. By the...
  5. GenSwgrEng

    Three Pole or Four Pole Breaker

    Use 3-pole breakers through-out. You don't need 4-pole breakers unless you have multiple services or on-site generation. You probably don't need it then, either in most cases. Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep...
  6. GenSwgrEng

    ATS won't transfer back

    I strongly doubt you've got a problem on the power-end of the ATS. It is most likely the ATS controller or operator (not you, the device that operates the contacts). If there were some sort of problem with the power, the ATS controller should not initiate a retransfer to begin with, and...
  7. GenSwgrEng

    arc quenching&ups synchronisation

    With regards to question 2, it is possible to parallel a UPS output with the utility. UPSs very often stay in sync with the utility anyway, so that they can do a perform an overlapping maintenance- or emergency-bypass. And UPS outputs can be controlled to allow for sharing load with another...
  8. GenSwgrEng

    Adding short circuit on closed transfer?

    You do not have to take both sources into account in your short circuit analysis if parallel operation will last less than 100ms. If parallel operation is going to last more than 100ms, you not only need to take into account the combined available fault current of both sources, but you need a...
  9. GenSwgrEng

    SYNC CHECKING (machine rotating opposite to system)

    Aboslutely, you'd want to put your voltage meters directly on the bus/cables. Of course, this is okay for low-voltage applications, but is more tricky for medium voltage applications. If lieu of meters, you could hot sticks and watch them grow dimmer and brighter as ScottyUK describes. I have...
  10. GenSwgrEng

    SYNC CHECKING (machine rotating opposite to system)

    A single-phase sync check relay will allow closure of two sources with opposing phase rotations. Most systems I've dealt with have two permanant sources. So once phase rotation has been verified, a single-phase sync check will suffice for future operations. If one of the sources is temporary...
  11. GenSwgrEng

    VR6 caterpillar voltage regulator...

    Try this URL: http://www.cat.com/cda/components/securedFile/displaySecuredFileServletJSP?fileId=92965&languageId=7 Engineers are always honest in matters of technology and human relationships. That's why it's a good idea to keep engineers away from customers, romantic interests, and other...
  12. GenSwgrEng

    Who determined to use green for open and red for closed in breakers ?

    I've had consulting engineers INSIST that all lights should be green under normal conditions. So on normally open breakers, green=open, and on normally closed breakers green=closed! Talk about confusing!

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