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  • Users: buddy91082
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  1. buddy91082

    Clearances to Manhole Access

    Hello all. I have a manhole with 600v conductors. Looking for clearance requirements above the manhole cover. NEC does not state clearances. Could not find clearances in OSHA. I will be installing a structure over the manhole and will be limiting clearance above the manhole. Thanks.
  2. buddy91082

    Single Pole, Molded Case Breaker Testing <600v

    This is a follow up to the thread below: thread238-444329 Would you normally perform primary injection testing on single pole, 15A/20A molded case breakers rated at 120v or 277v? (what you would see in a typical 100A/225A commercial panelboard that serves plug loads or lighting)? If not, what...
  3. buddy91082

    Impact of Motor Starting on Transformer Primary

    Hi all. This is a general question - when a transformer feeds a motor, does the primary side also see a voltage dip during startup, in ratio with what the secondary experiences? We have a light flicker problem when a motor starts and one solution is to install a transformer ahead of the motor...
  4. buddy91082

    Grounding Electrode Conductor Termination

    Per NEC 250.70, exothermic or mechanical lugs can be used to terminate grounding conductors to ground rod electrodes. Any benefit to either method? Thanks.
  5. buddy91082

    Low Voltage Primary Injection Test

    Is there a minimum size frame or trip rating to use primary injection testing on low voltage (<600v), molded case circuit breakers? NETA ATS does not define a minimum so one could assume it is across all frames and trips as small as 15A. Thanks. b
  6. buddy91082

    SKM Result - Negative Voltage Drop

    We are running a low voltage (<600v) drop study in SKM and are coming up with a few values with a negative voltage drop. Curious as to why the results might be coming up with a negative % voltage drop result on some of the buses and feeders and the negative % results means. Thanks. b
  7. buddy91082

    Led Driver Inrush

    Can anyone explain why driver inrush is not cumulative when having multiple drivers on a circuit. Is there a formula to determine the driver inrush when using multiple drivers? I have discussed the issue with several driver manufacturers and have not received a good explanation. Thanks.
  8. buddy91082

    Current in VFD

    Trying to determine how current changes when frequency in changed using a VFD. Voltage will change with frequency based on v/hz ratio. Hp change will be the cubed of frequency change. for simplicity, lets say HP = Volts x amps. If frequency changes 10%, voltage will change 10% and HP will be...
  9. buddy91082

    TCC Curves: What about events below .001 seconds?

    We have LED drivers with a rated inrush of 185 amps at 200 microseconds (.0002 seconds. We are trying to determine how many drivers we can place on a 20 amp, 120v circuit. The circuit breakers TCC curves start at .001 seconds. Also, the fuse TCC start at .01 seconds. What happens if the event is...
  10. buddy91082

    Break Horsepower vs Nameplate for Service Calculation

    Hi there. We are trying to right size our electrical service. We asked the mechanical engineer if there was any "fluff" in their pump and motor sizing. They said yes. For example, the calculated BHP on one pump is 23 bhp. They selected a 30hp motor (a 23% increase). We ere thinking we could...
  11. buddy91082

    Paralleling with Utility Theory

    Anyone know of a good book or article that discusses how the paralleling sources know, such as utility and distributed generation (pv, turbines, generators, and etc.)how much load generation to share? For example, with gas or steam turbine systems operating in parallel with the utility, how does...
  12. buddy91082

    Voltage Drop Techniques on Low Voltage System

    Hi there. I have a 240v, 1200 amp single phase service for a residence. The length of run is about 1000 feet from the utility transformer to the home. The utility has stated they do not have taps on their transformer. Stepping the voltage up to 480v and then back down to 240v is not an option...
  13. buddy91082

    Basic Generator Utility Interconnection Resource

    Hi there. Looking for a book or article that discusses the basics of generator for cogen interconnection to the utility and the response of the generators on various grid conditions. Trying to get the basics of how a generator acts when connected to the grid and when it islands. Thanks. b
  14. buddy91082

    Ground Test Well Electrode Connection

    Hello all. At ground test wells that are part of a ground ring, is it typical to make the ground ring connection to the electrode in the test well with an exothermic or bolted connection? I understand that bolted connections might be preferred for Fall of Potential testing. Thanks. b
  15. buddy91082

    Ambinet Air Temperature for Conductor Derating

    Looking to see if the 24 hour average ambient temperature can be used for conductor derating or do I need to use the maximum ambient temperature seen at ay given time (even tho it may only be for 5 minutes as an example. I assume if I need to use the maximum ambient temperature the thermal time...
  16. buddy91082

    Snubber Main and Output Insulator BIL Rating

    I have a 60BIL MV transformer. Snubber main insulator is rated for 75BIL. Snubber output insulator is rated for 40 BIL. What is the difference in the Main and output insulator ratings? Thanks. b
  17. buddy91082

    Equipment Voltage Ratings

    Equipment such as switchboards and panel boards have a nameplate voltage rating. Is there an allowable utilization voltage fluctuation above equipment nameplate rating? Example would be a panel low voltage panel board is rated 208v. If I need to increase voltage on the transformer serving the...
  18. buddy91082

    Conductors in Exhaust Plenum

    Hi all. We have a condition where existing 5kv conductors in RGS cannot be moved. To accommodate a new short run (25') of exhaust duct work that will only be exhausting air from a utility substation, the exhaust ductwork will wrap around the existing 5kV conductors in RGS. Don't worry about...
  19. buddy91082

    Rigid Aluminum Conduit (RAC)

    Using RAC for a few single phase 120v branch circuits. Concerned about the non-ferrous properties of aluminum and ability to shield emi from branch circuit conductors with conduit that will be light fixtures from a dimming control panel. There is some audio equipment about 15' away from where...
  20. buddy91082

    Transformer Inrush - theoretical or real - and sacrifices

    I just reviewed a coordination study with a 750kVA transformer (5kv primary - 208Y/120v secondary. The primary protection is a 125E fuse. The coordination curves shows the transformer inrush trippng the 125E fuses. The trip is just on the border line of the fuse melting band. If i use a 150E...

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