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Recent content by Mila15

  1. Mila15

    Motor Space heater 4160v fault question

    Thanks all. Edison123, the space heater for this application is part of equipment control circuit, and we use UPS power on all major control circuits. I think even if space heater is switched off, it's only switched from high side (not neutral) and if there is a short it might find it's way back...
  2. Mila15

    Motor Space heater 4160v fault question

    We have a situation where a motor heater is part of 4160v compressor control circuit. We have a standard that any critical control circuit should be supplied with UPS. Question is, if there is a fault in motor winding (4160v), can fault current find it's way into 120v heater circuit (UPS)? Is...
  3. Mila15

    Mechanically held coil for motor MCC

    Thanks for the help! In our MV application, we have control power suppliesd by external UPS panel. The reason why we're not using a CPT configuration is because we have suffered multiple sag incidents that caused MCCs to drop, losing very critical loads. But that also created an issue when...
  4. Mila15

    Mechanically held coil for motor MCC

    Are motor MCCs with Mechanically held coils (one close, and one trip) common? Vendor said those are mainly used on breakers, or starters feeding transformers. The only reason I can think of is safety concern, as you need to be able to stop motor remotely if needed, but that can be solved. Any...
  5. Mila15

    Low Voltage Power Breaker 30 Cycle Rating

    The 30 cycle rating means the CB can withstand SC for 30 cycles. If there is no trip setting based on time and current to trip the CB, its contacts can last 30 cycles before they melt closed.
  6. Mila15

    Parallel transformers operation and NEC

    This is my interpretation as well, but some say the AND between "operated in parallel" and "switched as a unit" means they must go together! No one knows what NEC intends in most cases! I think they worry about danger of back feeding if only one transformer is turned off, but proper switching...
  7. Mila15

    Reallly long panel feeder -- how to connect to panel and feeder breaker?

    We have used Polaris connectors or Burndy reducing adaptors: http://ecat.burndy.com/Comergent/en/US/adirect/burndy?cmd=catDisplayStyleMob&catKey=603108
  8. Mila15

    Parallel transformers operation and NEC

    NEC permits using transformers in parallel operation and switching as one unit. Is switching as one unit a mandatory? Does that mean I have to use a 6 pole switching application, or I don't have to do that if proper tagout procedure is used? This is for 480v, 300KVA XFMRs application. Does...
  9. Mila15

    Multiple motors by one starter

    Good points davidbeach and jraef. It might be a good idea to change OL relay to electronic type (if possible). But I'll let them know that they won't have complete redundancy, especially if the problem is at either the starter or the switch.
  10. Mila15

    Multiple motors by one starter

    A client with no spare MCC capacity needs to add a spare motor. The only option available is to use the same starter for two motors (main and spare). I was thinking of using a transfer switch so that only one motor can be operated at one time. Does NEC article 430.87 which states that: "Each...
  11. Mila15

    VFD start current

    Thank you guys for the help!
  12. Mila15

    VFD start current

    Thanks all! below are drive/motor/breaker info: VFD: Powerflex 753 rated for 40 HP motor (52 A) Motor: 40 HP, 46 FLA, 306 LRA Breaker: Type HFD 3070, 70A The AB representative confirmed jraef's statement: max of 200% of FLA during motor start, which would not trip breaker even if motor start...
  13. Mila15

    VFD start current

    I just realized that the vendor is using a thermal-magnetic breaker to feed a VFD/Motor application rated at slightly above 125% FLA. Looking at motor starting curve Vs breaker curve, it seems pretty tight. My question is, what would be the maximum starting current drawn by a 753 Powelflex...
  14. Mila15

    Main Tie Main Closed Transition Re-Transfer

    We have installed few systems using the M-T-M configuration. When an Auto transfer occurs, I don't think we have a problem because this happens if one source is lost. It's the manual transfer we are worried about. In the last design, it worked out fine because One feed could not handle the...
  15. Mila15

    Question on NEC 210.20

    This is in an Electric Utility Generation Plant, where 92.B.5.b applies.
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