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  • Users: VTer
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  1. VTer

    Thermal Resistivity of Soil

    The geotech reports typically include a dry out curve and tables with multiple values of thermal resistivity for a soil sample based on the percentage of water content. My understanding is that the 0% water content values are oven dry soil and not practical. Is there an industry standard for...
  2. VTer

    NEC 110.26 Working Clearance

    Hi All, Is anyone aware of equivalent IEC or other international code/standard that may include the equivalent requirements for working clearances similar to those found in NEC 110.26? "Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if...
  3. VTer

    Selection of Transformer to Supply a Cyclic Load

    Hi All, I saw a reference that "When the load cycle is sufficiently short so that the temperature of the transformer does not change appreciably during the cycle, the minimum transformer size is the rms value of the load." The equation that is provided is S=sqrt((S1^2*t1+S2^2*t2)/t(cycle))...
  4. VTer

    Current Harmonics based on Source Impedance

    Hi All, I posted this question on the Motors & Generators Forum and it got no traction, so I will try it here. Does anyone have any reference on calculation of harmonic currents and THD-i for 6-pulse diode rectifier based on the impact of source impedance? "Throughout space there is energy...
  5. VTer

    Current Harmonics based on Source Impedance

    Hi All, Does anyone have any reference on calculation of harmonic currents and THD-i for 6-pulse diode rectifier based on the impact of source impedance? "Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is...
  6. VTer

    IEC Version of NEC Table 9

    Hi All, I was wondering if there is an IEC version of NEC Chapter 9 Table 9 that has all the various cable sizes in mm2 and 50Hz resistances and reactances? If there is not, do you know of nay such table in other standards that is used in the IEC world? Thanks! "Throughout space there is...
  7. VTer

    NEC Panelboard Question

    Hi All, Let me start by stating that this is a NEC question. I have a situation with a 120/208V main switchboard with a 200A feeder CB that feeds a 200A MLO panel with feed-through lugs that further feeds another 200A MLO panel about 150 feet away. I would like to install sub-feed lugs in the...
  8. VTer

    Generator Nameplate

    Does anyone know what RVFL stands for in Generator Nameplate "EXC. FLD AMPS-RVFL". "Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed...
  9. VTer

    Pump Motor Locked Rotor Condition

    We have a general purpose 3HP, 3ph, 60Hz 460V induction motor driving a centrifugal pump for a chiller system pumping water/glycol mix. The motor is started across the line from a MCC bucket roughly 20 feet away. The motor has been recently tripping out on overload. The motor has a FLA of...
  10. VTer

    NEC Emergency System Selective Coordination Requirement

    2011 NEC 700.27 states that emergency system OCPDs shall be selectively coordinated with all supply side OCPDs. My question is regarding the wording of "all supply side OCPDs" Does this include the normal source of the automatic transfer equipment? My interpretation is that coordination...
  11. VTer

    Part-Time Graduate School vs Part-Time Consulting Work

    I am in my early thirties and work full-time for a large corporation that has been very flexible with my schedule and my manager is very supportive. I focus to make my full-time job my top professional priority. With the company’s permission and my manager’s support, I also just recently...
  12. VTer

    Maximum Length of Xfmr Secondary Conductors

    The application is in US and the question is regarding the NEC requirements. Scenario: 480V Panel with feeder breaker and primary conductors feeding transformer: 45kVA, 480V Delta - 208/120V solidly grounded wye. Transformer then feeds a 208V panel which is 42ckt tub with 150A MCB. Question...
  13. VTer

    Power Factor Corr Cap Making Hissing Noise

    We just installed a 500kVAR 60Hz 480V 3phase delta connected power factor correction bank on our 480V switchgear. The 500kVAR capacitor unit is made up of (5) 100kVAR units tied to a common bus in one enclosure. Each 100kVAR unit contains multiple electrolytic capacitors. Upon energization of...
  14. VTer

    System Grounding

    We have primary utility service and a 25kV-480Y/277V outdoor located pad-mounted transformer. The natural X0 bushing is bonded to ground at the transformer. In addition, 480/277V 4W switchgear lineup in the building also has the system bonding jumper between the neutral bus and ground bus. The...
  15. VTer

    LV Transformer Primary Conductors and Protection

    We have a 45kVA, 480V delta – 208Y/120V 3-ph 60Hz transformer. NEC 450.3(B) allows maximum overcurrent protection on primary to be 250% if we limit the secondary protection to 125%. We have a spare 100A/3P CB that we would like to use which would meet the code requirement. However, it is...
  16. VTer

    PF Cap Install Question

    We have a double ended 480V substation with a normally open tie. I would like to install 300kVAR of PF correction capacitors for this substation. The question I have is to either install 300kVAR cap on one side of the sub and only use one circuit breaker or install 150kVAR on both sides and use...
  17. VTer

    MV Cable û Defective Termination

    Attached is a photo of a defective termination on the HV air terminal chamber on 25kV/480V transformer. It looks like the silicone tape somehow ripped and is exposing the lug and what seems like the cable insulation. I am the new to this facility and I am not sure about the cable type, size or...
  18. VTer

    Motor Failure

    All, Please see attached photo and let me know if you can identify the root cause of the failure. Motor data is: 10HP, 460V 3-ph RPM 1755 with Class F insulation "Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know...
  19. VTer

    %Vrise on bus due to capacitor installation

    Hi All, I am thinking about installing PF correction Caps on 480V bus and I would like to confirm the voltage raise. I could not find any reference on doing these calculations based on available SC current and X/R at the bus. I have found some estimates that base the Vraise on the transformer...
  20. VTer

    Close-Transition Automatic Transfer Switch with Delta and Wye Sources

    Assuming the same phase sequence and frequency, is it possible for Close-Transition Automatic Transfer Switch to perform close-transition transfer if one source is 480V, 3-Phase 3-wire Wye and other source is 480V, 3-phase, 3-wire Delta? "Throughout space there is energy. Is this energy...

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