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  1. georgeshall

    Transformer Secondary Protection

    If you are taking 2 sets of 500’s from the transformer secondary, without overcurrent protection at the transformer secondary, the panelboard main circuit breaker trip rating (800A) must not be greater than the ampacity of the conductors (760A). See Art. 240.21.C where it is stated that “the...
  2. georgeshall

    Thermal Overload Device w/ VFD and PLC

    You don't want to ever disconnect a motor, either with a switch or contactor, while the VFD is running as high voltages can be generated which can severly damage the VFD. Also, the VFD may not be able to handle the high inrush currents when closing a switch or contactor start a motor while the...
  3. georgeshall

    Transformer Burn Out Question

    I second Warpspeeds opinion. I've seen a power center transformer fail due to harmonics issues with UV banks at a water treatment plant, and this happens a lot if the correct type of transformer is not supplied. We actually change the way we design now and specify that the UV bank suppliers...
  4. georgeshall

    Hazardous Location Information

    I left out the class/division times based on the same article: If the gas is present more than 10hr/year it's a Class1Div1 location, if the gas is present between 1 and 10hr/year it's a Class1Div2 locations, less than 1hr/year it's unclassified. Hope this helps.
  5. georgeshall

    Hazardous Location Information

    That IEC standard would be a place to start, but I don't have access to it so I don't know if it defines the time. The NEC article 505 has a couple of other standard references as well. From what I've read in various IEEE articles (based on API RP 505), if the gas is present for more than...
  6. georgeshall

    Hazardous Location Information

    Class 1, Zone 0, 1, and 2 locations have time constraints for the presence of ignitable concentrations of gases or vapors. Class 1, Div 1 and Div 2 locations are defined based solely on the presence of ignitable concentrations of gases or vapors. Do you have access to the NEC? If so check out...

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