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  • Users: RonShap
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  1. RonShap

    Neher McGrath Calc UG Ductbanks

    For underground ductbank calculations for ampacities, we typically use a rho of 55 for concrete and 90 for soil. We concrete encase our ductbanks, then cover with soil up to grade. We have the contractor send a submittal with lab tested sample / typical material that will be used around the...
  2. RonShap

    Estimating Connected and Demand Loads

    I'm trying to find a comprehensive reference for estimating connected and demand loads very early on in a new project based on VA/sf (or W/sf) I've used the very abbreviated list in IEEE 241 (old Gray Book) Table 15, but would like to find something more comprehensive and if nothing else, more...
  3. RonShap

    Medtronic CGM App

    My son wears a Continuous Glucose Monitoring (CGM) device, http://www.medtronicdiabetes.com/treatment-and-products/continuous-glucose-monitoring http://www.medtronicdiabetes.com/treatment-and-products/enlite-sensor We can download metering information from the insulin pump direct to a receiver...
  4. RonShap

    GE Instrument Transformer JVM-5 Saturation Curve

    We are having a study done on a facility. I cannot locate a saturation curve for a JVM-5 PT. Does anyone have a resource they can suggest for me to look?
  5. RonShap

    Neher McGrath Typical Value for Concrete

    I think it is interesting that when doing underground temp calcs, that most use 55 for the Rho of concrete, because it is printed as a typcial value in the NEC. The "father" of underground duct bank calcs wrote in his paper in 1957 (AIEE Paper 57-660, Table IV) that the typical value is 85...
  6. RonShap

    44kV termination type

    Primary side termination to a 44kV-480/277V 2500kVA oil filled transformer. Since it is such a relatively small transformer, I am concerned that the tank will not be strong enough to support a bottom entry "pothead", which is required due to the configuration of the existing 44kV SWGR that...
  7. RonShap

    IEEE 1584b-2011 Arc Flash

    Does anyone know of a link that describes or discusses the changes in IEEE 1584b-2011? I'm trying to figure out whether it is worth purchasing.
  8. RonShap

    Data Center Uptime Institute Tier Topology

    For those familiar with the Uptime document, I'd appreciate your opinion. The terminology used below is directly from the document and does not always reflect reality. Data center with a "N" steady generator load of 10MW. Since it is specified as a Tier III topology, there is "N+1" generators...
  9. RonShap

    SWBD Short Circuit Rating

    480V, 3Ph, Paralleling SWBD rated at 100kAIC. Using SKM the 3 phase bolted fault calculated at 91.8kA with x/r=15.4 L-G fault calculated at 121.8 with x/r=12 Does a normal 3 phase switchboard short circuit rating of 100kA have any associated L-G rating, or do I use the 3 phase rating? Does this...
  10. RonShap

    Closed Transition AIC Rating

    I recall several NEC code cycles ago, there was a proposal made to add an clarification/exception to Section 110.9 or 110.10 where short periods of closed transition (maybe 20 ms) would not be required to be included in the short circuit calculations and the resulting withstand or AIC selections...
  11. RonShap

    MCCB Primary Injection Testing

    For circuit breakers in the 600-1200A frame size, does anyone know a published example of a failure rate for breakers showing up on site? I know that manufacturers perform a small sample of circuit breaker trip unit tests, but I'm curious if anyone has anecdotal or even better published failure...
  12. RonShap

    Sync check

    Is there a simple applications guide for a sync check relay configuration? A SWBD with two mains (open transition) doesn't seem complicated, but I can seem to explain the circuitry connections needed to a local panel builder. A diagram or picture is worth a thousand words.
  13. RonShap

    Subtracting two electrical sinusoidal functions

    In an electrical transfer switch there are two sources. When measuring from phase A of one source to Phase A of the second source, there may be a phase angle difference and a resulting voltage difference. I'm trying to workout the formula on excel to determine the value of one sin wave minus...
  14. RonShap

    Load Flow?

    There is a generator paralleling SWGR in which there are (4) 1500kW diesel generators connected and approx 20 distribution circuit breakers tapped at various positions at either end of the SWGR. I have not performed a load flow study before and I'm trying to determine if that is what is needed...
  15. RonShap

    Parallel Generators different pitch

    What might be the expected result of two paralleled generators, one 2/3 pitch and the other different, both resistance grounded. I guess that they will not share load well. A grounding resistor vendor claims that he will provide a fully rated grounding resistor and it will absorb circulating...
  16. RonShap

    Series Rating - Fuse & Breaker

    Consider a 1600A current limiting fuse with 200kA available short circuit current on the line side. The fuse manufacturer states that the maximum let-through at any current up to 200kA on the line side is less than 100kA on the load side. Why is a series rating required for a downstream 100kAIC...
  17. RonShap

    Sprinkler Head Location

    When designing sprinkler head locations, our FP Engineer locates the heads to protrude through a suspended ceiling tile, so all are essentially on the underside of the suspended ceiling. No sprinkler heads are located above the suspended ceiling which is used as an air plenum for return air...
  18. RonShap

    GE MVT Settings

    I will be going to a site that has GE Microversatrip trip units. I will need to determine the LSI settings that are programmed for each 480V breaker. Does anyone have a suggestion where to find a step by step button/screen selection list, to view the settings. I have to prepare a written...
  19. RonShap

    Ground Fault Protection Feeders/SDS

    In most areas of the USA, the NFPA 70 (NEC) is code. Section 215.10 requires ground fault protection for feeders that are "1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase" unless...
  20. RonShap

    Generator Decrement Curve

    I'm trying to determine if the inrush of transformers totaling approximately 5MVA of varying size XFMRs would damage or significantly be out of the range of performance of (2) 1875kVA, 0.8PF standby diesel generators. The transformers are significantly underloaded, but the connected load to...

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