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  • Users: slushin
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  1. slushin

    NFPA 70E Tables Maximum Clearing Time

    So, I know that the tables for NFPA 70E cannot be used if the exact parameters are not met (ie working distance, fault clearing time, max short ckt current, etc). However, I'm confused as to what the meaning of maximum fault clearing time means. Does it mean: 1) the actual maximum time that...
  2. slushin

    Grounding in More than One Location?

    So here's the situation: I have 5 generators paralleled to a paralleling switchgear. The generators are installed outdoors and the switchgear is indoors. The installer grounded the neutral of each generator and also grounded the neutral of the paralleling gear. When I discussed this with the...
  3. slushin

    synchronous motor leading pf

    Can anyone explain theoretically how a synchronous motor can be changed from a lagging to leading power factor? I understand that it can be done by adjusting DC excitation, but I don't understand how a device consisting of resistance and inductance can draw a leading PF.
  4. slushin

    Comm and power separation

    Is the purpose of the separation between communications and power required by NESC 320.B.2 intended to prevent heat transfer from the power conductors to the comm conductors or to prevent induction of voltage from the power conductors onto the comm conductors?
  5. slushin

    120V Phone and Fiber In Same Conduit

    Does anyone know of any standards which state whether or not it is acceptable to run fiberoptic and phone lines in the same conduit? I know what the NEC says, but I'm interested in whether or not this will cause performance issues for the fiber.
  6. slushin

    Universal Vs Multitap Ballast

    Is there a difference between universal and multitap lighting ballasts? My impression is that a universal ballast will accept many different voltages without physically adjusting anything (ie taps), but that the multitap ballast will require setting the taps on the ballast prior to applying...
  7. slushin

    Two Bonding Jumpers. Should I get rid of one?

    I have a situation where an old switchgear, which used to be the main service for the building, is now downstream from a new switchgear which now serves as the service entry. The new switchgear neutral and ground are bonded as required by NEC. However, the old switchgear still has a bonding...
  8. slushin

    NEC 250.22(5)

    Does anyone know why NEC 250.22(5) specifically says not to ground the secondary circuit of a pool lighting system? I know that the NEC allows circuits to be ungrounded if interrupting the operation of the circuit would be less harmful than an uplanned interruption of the circuit. This makes...
  9. slushin

    Relevant Work Experience for P.E.?

    Has anyeone come from a manufacturing background and been able to use their time spent in manufacturing towards the 2 years of experience required for your P.E.? I'm an EE and I spent 2 years as a electrical process engineer doing mostly programming, very little design, some design review, and...
  10. slushin

    Calculating Motor Full Load Rating

    Can anyone tell me why the full load amps listed in the NEC do not equal the motor power rating divided by the motor voltage rating? For instance, a 10hp 230V single phase motor is rated at 50Amps according to NEC, but using I=V/P, you get 32Amps.
  11. slushin

    Load Interruptor Switch Location

    Hi all! Does anyone know if there is any language among the codes which states where a load interrupt switch needs to be located? I have a load interrupt switch which separates a generator from downstream loads. The generator is on floor level and the contractor is proposing putting the load...
  12. slushin

    equipment grounding for a data rack

    Hey all, I have a specific question about grounding for a metal rack that houses servers. In my case, I am dealing with 4 server rooms in 4 different locations. At each location, a conductor is being used to bond the rack to a water pipe that is nearby each location. Is this allowed by the...
  13. slushin

    Constant Vs Variable Torque VFD Ratings

    I'm having difficulty understanding why variable torque VFD's have a higher current rating than constant torque VFD's. Is it assumed that the variable torque VFD will be running below it's maximum speed all of the time?
  14. slushin

    Grounding for New and Existing Telecommunications

    I recently installed a new telecommunications system in an existing building. The new system is installed per ANSI/TIA/EIA J-STD-607-A, meaning that there is a Telecommunications Main Ground Bus (TGB) at the service and in each equipment room , aTelecommunications Backbone (TBB) which branches...
  15. slushin

    Communications Grounding

    Can anyone help me figure out what the purpose of a telecommunications grounding system is? Since the TMGB is ultimately bonded to the service grounding system, I’m not understanding why communications equipment cannot just be bonded directly to the ground at the service entrance as opposed to...
  16. slushin

    120V vs 208V motor

    Given a specific horsepower, does the selected voltage for a motor affect anything other than the current that the motor will draw? I have a contractor that is proposing to install a 120V 3/4hp motor as opposed to a 208V 3/4hp motor and, other than current draw changing, I'm wondering if I...

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