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  1. mb3928

    Bolt hole spacing on 50s-70s US vintage switchgear

    Looking to the old-timers here, we often have to replace lugs in switchgear in the Northeast US from the 50s, 60s, and 70s, and we consistently find lugs with boltholes spaced at 1-1/4". Today the NEMA standard spacings are 1-3/8" and 1-3/4". Does anyone know why this change happened? Was there...
  2. mb3928

    Zero Sequence Confirmation

    Energyfit2438, you should be able to detect a utility side ground fault from the DG side as long as both neutrals share the same ground reference. One way to do what (I think) your AHJ is asking for us to connect the utility side and DG side neutrals together. In that case you must not bond the...
  3. mb3928

    Phase loss behavior of YG-YG autotransformers

    Probably not, they're just dumb iron! Do you think the below scheme would work for phase loss detection? It might also provide some ground fault protection but that is not the point. The inverter shown is a voltage-controlled current source with high Z1 such that I_LLL is on the order of 1.5pu...
  4. mb3928

    Phase loss behavior of YG-YG autotransformers

    Thanks! Just to confirm, you're saying that the same effect happens, regardless of whether it is a standard isolation transformer or an autotransformer?
  5. mb3928

    Phase loss behavior of YG-YG autotransformers

    For a standard YG-YG three phase transformer with a 3-leg core, I understand that a phase loss on the primary side will be regenerated due to the magnetic flux path through the 3rd leg of the core corresponding to the lost phase. Less or no regeneration will occur for a 4 or 5 leg core or shell...
  6. mb3928

    Anyone have Strescon precast plank load tables from 90s?

    Does anyone have load tables for 8" Strescon precast plank from the 90s? Note there are several Stres(s)cons out there, this is the one that was based in Morrisville PA in the 90s and appears to no longer be in business.
  7. mb3928

    ASTM test for bulk density of cinder fill

    We will be performing some cores of an existing roof from the 1960s. The original prints call for cinder slag fill to provide roof pitch on top of the flat concrete roof planks. In my experience many structural engineers make very conservative assumptions about the weight of cinder fill. Can...
  8. mb3928

    NYC Parking Garage Collapse

    I know you’re joking but I work in a lot of old NYC buildings and in my experience construction quality was much higher until the 1940s-1950s, where things start to go downhill. Make of that what you will. Some of you may find the 1938 NYC Building Code of interest. Many of the building laws...
  9. mb3928

    Bracing of Gerber girders for LTB

    Thanks all, after a more careful examination of the unbraced lengths the engineer was able to reduce the amount of bracing specified, although a good amount is still required. An interesting learning experience for me. KootK, thanks, not my style to try and trick anyone. Be gentle with my...
  10. mb3928

    Bracing of Gerber girders for LTB

    This problem came up in the context of adding solar to a large warehouse built in the 1970s. Construction consists of steel W shape columns with cap plates, W21x68 Gerber (cantilever) girders with a column-to-column span of 50' and a cantilever of 7'. There are no web stiffeners at the column...
  11. mb3928

    Open phasing of a D-yg transformer with inverter generation

    My question concerns interconnecting inverter-based distributed energy resources through delta / wye-ground transformers, where the delta side is towards the utility and the wye-ground side is towards the DG. I have often seen objections to this configuration on the theory that an open phase on...
  12. mb3928

    Effect of drying on soil TC values for duct bank design?

    jghrist, that's exactly what I was looking for, thank you. dpc, thanks and understood. Code required or no, I just wanted to run the Appendix B checks to make sure the equipment terminal ratings/ampacities are still the governing factor, since these are (in my world at least) pretty sizeable...
  13. mb3928

    Effect of drying on soil TC values for duct bank design?

    I am designing some 480V underground duct banks for a distributed generation project, using NEC Appendix B to calculate derating. They will be designed to carry ~2,500A each. The geotech report for the site lists a number of Rho values with the soil at varying moisture contents. Down to 3%...
  14. mb3928

    Structural design requirements for NFPA 15 pipe stands

    I work for an EPC company that will be installing some water spray systems to protect some electrical equipment. These systems are to be designed according to NFPA 15, with a design density of 0.5 gpm/sqft. This translates into about 2000 gpm & around 28 nozzles for our systems. My fire...
  15. mb3928

    Can someone identify this 1930s-vintage pressure vessel?

    Waypoint Park in Bellingham. There are a number of interesting remnants of the old paper mill that are on display there. (And a nice beer garden!)
  16. mb3928

    Can someone identify this 1930s-vintage pressure vessel?

    ironic metallurgist, that's why I was surprised & curious... the sign on site said it was a relief vessel for the large, cylindrical digesters next to it. So why fabricate it as a sphere if it's operating at the same pressure as other, larger, cylindrical vessels? I figured if anyone could...
  17. mb3928

    Miami Beach, Champlain Towers South apartment building collapse, Part 10

    Anyone who has ever hammer-drilled anywhere in a building has received this complaint. It means nothing.
  18. mb3928

    Can someone identify this 1930s-vintage pressure vessel?

    Visiting family in Bellingham WA and found this 1930s-vintage, riveted, spherical pressure vessel repurposed as art in a new park. Apparently the site used to be a paper mill, and the sign says this unit was a relief vessel for the taller digesters to the right in this photo...
  19. mb3928

    Miami Beach, Champlain Towers South apartment building collapse, Part 05

    Most apartment panels in a 120/208V 3P4W system will have 2 hots and a neutral. These will get staggered in the meter bank, e.g. Meter 1 is L1L2+N, Meter 2 is L2L3+N, etc. More importantly, though, is that the runouts (and sometimes the risers) from meter banks to apartment panels are very...
  20. mb3928

    Miami Beach, Champlain Towers South apartment building collapse, Part 05

    My point is that 1) the 1979 FA riser doesn't show a waterflow alarm of any kind in the garage, 2) there is evidence of significant damage in the garage before the collapse, and 3) there are no reports of a fire alarm going off until during/after the collapse. That's not ironclad, but taken...

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