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  • Users: X49
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  1. X49

    Temperature Rise of Oil Film on Cylinder Liner

    I'm interested in how much the temperature of a thin oil film will rise over a short period of time after it applied to a warmer metal surface, such as splash-lubricated cylinder wall in an engine. I'm okay with assuming that the metal surface stays at a constant temperature, if that makes the...
  2. X49

    GFI tripping on well pump used in a lake.

    You may want to check the NEC. Canadian code allows ground fault current up to 10mA for up to 2.7 seconds in this application.
  3. X49

    High efficiency motor and soft starter problem

    When multiple centrifugal pumps are pumping into a common header, less power is normally required per pump, which will help. However, it is really odd that the 150hp starter will not start the pump. Is it possible that the motor is just overloaded when only one pump is operating? It is odd...
  4. X49

    Problem with several Pleuger Submersable Motors

    I have come across submersible motors that were required to have dv/dt or even sine-wave filters installed when operated with a VFD, according to the manufacturer. Load reactors were apparently not sufficient. These motors had an insulation rating of only 850V for a 575V (rms) application...
  5. X49

    Device KA rating verification study

    To me, "branch fault current" implies that this is the fault current downstream of the overcurrent device (i.e. at the load). The fault current available at the load could be much lower than the fault current available at the breaker. You should use the fault current that is present either at...
  6. X49

    Intermittent Loads

    Section 8 of the CEC covers "conductor ampacities and equipment ratings required for consumer's services, feeders, and branch circuits". This would include transformers (unless they are utility-owned). Section 8-106 deals with demand factors. There are not many loads that you are allowed to...
  7. X49

    VFD Blown

    I have experienced multiple drives on failing simultaneously in a new facility. They were small drives installed on a large 600V system without line reactors. It was presumed that they had failed due to line disturbances. They were the only two drives without line reactors, and the only two...
  8. X49

    Overdutied Equipment

    I can't speak to whether or not current limiting fuses are appropriate in this situation, but you could consider installing reactors upstream of the PFC units to limit the short circuit current. Some automatic power factor correction units come with reactors that are intended to reduce...
  9. X49

    460V equipment, 208V supply

    I wouldn't expect any complications in using a step-up transformer. Keep voltage regulation in mind. A transformer might drop 5-6% voltage from no-load to full load. This will be in addition to the voltage drop to the service entrance, which could be up to 5%. This could be an issue if you...
  10. X49

    Misconception in Electrical Scope in Area Classification Assessment

    Area classifications usually fall into the EE's scope of work since they are defined in the electrical code (in US and Canada). The definitions in the code can be vague, and somewhat confusing. They rely on the engineer to make a judgement call regarding the concentrations that may be present...
  11. X49

    generator hunting

    I've had a generator hunt while starting large motors with soft starters. The solution was to lower the governor gain setting on the generator controller.
  12. X49

    Genset: Immediate disconnection risky for the engine ?

    I would not expect anything to be damaged, but I suppose there is a small possibility that the genset could trip on overspeed with a rapid reduction in load. If this happens, governor settings should be changed so that it does not happen. It is not good for a turbocharged engine to shut off...
  13. X49

    % Current and Voltage THDs in In-Plant Industrial Systems

    At a minimum, I would recommend keeping harmonic voltage distortion below 5%, as recommended by IEEE 519. The current distortion requirements in IEEE 519 are more stringent and don't necessarily need to be met in order to have a healthy system.
  14. X49

    5 ohms Ground Resistance in Commercial Buildings

    You are assuming that the entire 12kA fault current will use the ground grid as a return path. This will not happen. The 12kA fault current will return to the transformer on the neutral conductor, which should be terminated to ground at the service entrance. Very little fault current will...
  15. X49

    Chilled Water Pump Starter

    I see from your other thread that you're concerned about the total load on your transformer / breaker. Soft starting will not help with this. The max loading on your transformer is generally determined by adding all loads, plus 25% of the largest motor FLA. You must apply this 25% factor...
  16. X49

    Chilled Water Pump Starter

    The upstream breaker should not be an issue if it is sized to code. The upstream transformer will drop voltage during the motor start. The extent of the voltage drop can be calculated with the transformer impedance, X/R, and motor starting current. A voltage drop of 20 or 25% should not be an...
  17. X49

    Continuous Rating on Fused Disconnect

    wroggent, You could use a 100A breaker in jraef's example, but only if it is listed for operation at 100%. In this case, the conductors would only need an ampacity of 100A. (NEC 215-2, 215-3) As a rule, I would recommend keeping things simple and using regular breakers. However, 100%-rated...
  18. X49

    Continuous Rating on Fused Disconnect

    The same rule applies for fusible switches as for breakers. The continuous current must be limited to 80% unless the fusible switch is listed for operation at 100%. I am not sure how common 100% rated fusible switches are. Non-fusible switches are generally rated for 100% continuous duty.
  19. X49

    Buck Boost Transformers for loads requiring neutrals

    All good points. I think I'll stick with 208V.
  20. X49

    Buck Boost Transformers for loads requiring neutrals

    I've been thinking of using a buck boost transformer to boost from 208V to 236V single phase for a 230V stove that requires a 120/240V 50A receptacle. GE recommends using these transformers for some of their appliances. The obvious concern is that the appliance requires 120V for lighting and...

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