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  1. dup18

    Spacing of electrical equipment in a substation

    Thanks for the responses. I could not figure out that the bases (and the first 8 feet high) are basically grounded metal. Breaker control cabinets may contain 120 AC or DC. Yet the equipment is spaced far apart. Room for a truck to travel, and I guess room to remove/install some of the...
  2. dup18

    Spacing of electrical equipment in a substation

    All, I am probably missing the obvious, but what document(s) are used to determine the horizontal clearances (spacing) between various pieces of electrical equipment (disconnect switch, circuit breaker, circuit switcher, metering PT/CT, etc. in a 115 kV substation? Podo
  3. dup18

    Metal clad switchgear - fire rated room?

    Hello, When installing replacement medium voltage metal clad switchgear in an existing room, is the room required to be fire rated? The switchgear is rated at 5 kV, and all circuit breakers and bus work will be 2000 amperes. All NEC requirements for egress and working space will be met or...
  4. dup18

    Cell phone tower grounding

    Hello All, Is there a good guideline to use when installing the grounding or inspecting someone's work regarding cell phone tower grounding? Should the fence fabric be grounded? Regards, Dave
  5. dup18

    Minimum vertical height of 25 kV bushing

    Hello, We have a fenced in substation that is being installed at a mine site. The maximum three phase voltage in the substation is 25 kV phase to phase. The substation is completely fenced in with a 6 foot chain link fence and 1 foot of 3 stranded barbed wire. The entrance gate is locked at...
  6. dup18

    Wiring in hazardous location - NEC Std. - On-Skid of Moto-Compressor

    The engine block heater in the picture is required to be explosion proof (Class I, Div 1)because the box contains circuit breakers and line starters (contactors) that arc and spark normally. As such, there must be an explosion proof seal(s) within 18 inches of the enclosure, per Chapter 5 of...
  7. dup18

    Outdoor high voltage conductors

    We have an application that we need to run about 20 feet of high voltage conductors (500 kcmil - 3 of them)in a mine substation. The cables will run from the transformer phase leads to the top of an outdoor switch house. The voltage is 12,470 volts. I cannot use a cable. I guess that I have...
  8. dup18

    Conductor Spacing

    Guys, Good deal. Thanks for your help. Dave
  9. dup18

    Conductor Spacing

    WHat is the minumim spacing requirement between bare conductors (lugs) for 15 kV class equipment if you want to maintain 90 kV or better BIL? Is there some document that would summarize the necessary spacings for different voltage/BIL levels? Thanks, Dave
  10. dup18

    Stress Cone Location

    Guys, Thanks to both of you for your information and advice. Dave
  11. dup18

    Stress Cone Location

    On a 5 kv system installation using shielded cable, do the stress cones have to be at the end of the conductors next to the cable lugs or can they be located 2 to 3 feet back from the cable lugs? This added distance would allow someone to replace a cable lug without having to re-do the stress...
  12. dup18

    Transformer Differential Protection

    A customer has installed a solid state transformer differential relay to protect a small pad mount transformer. All of the hardware is installed. This is a non-critical application. I have never set a transformer differential relay, so this might be an excellent opportunity to learn how to...
  13. dup18

    Control wire fault location

    On some long conveyor belt installations, the control wires are installed in metal conduit that is fastened to the conveyor belt structure. Some of these conduit runs are in excess of 3000 feet long. There are pull boxes and junction boxes every so often. These control wires are #14 AWG...
  14. dup18

    Source of ignition?

    Marke, What I was getting at was that if a ground fault on a conventionally started motor would have the same result as a VFD powered motor, there was something wrong with the installation. If the theory is that the frame voltage were coupled through piping (for example) into a hazardous...
  15. dup18

    Source of ignition?

    Mark, Referring to your comment to me (dup18), if you are concerned about common mode voltages raising the frame voltage, and this subsequently causing an explosion hazard, would you also be concerned if it were a across the line starter and the motor had a ground fault? If so, there are other...
  16. dup18

    Grounding Transformer Requirements

    It is a requirement that the grounding resistor (and associated equipment) be rated for continuous duty. In reality, we set the relays to trip in a matter of seconds, long enough to allow for downsteam coordination.
  17. dup18

    Source of ignition?

    Mark, I have worked as an electrical engineer in the underground (coal)mining industry for over 30 years, and VFD type controllers (or any other type of electrical equipment) are 1) housed in an explosion proof enclosure, or 2) installed where there is no possibility of methane gas accumulation...
  18. dup18

    Grounding Transformer Requirements

    I want to develop a 25 ampere resistance grounded system for a delta connected 7.2 kV supply. I want to use three single phase transformers (4160/7200V to 480 volt)to serve as a grounding transformer. The transformers will be connected wye-delta with the grounding resistor connected to the...

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