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...
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...
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.
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...
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...
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...
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%...
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...
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...
For a typical large-scale lithium ion battery energy storage system, a battery container may have a rating of 5 MWh usable, 2 MW DC continuous discharge power, with a nominal 1000V DC bus voltage ranging from 700V-1100V DC in service. DC fault current can be as high as 200 kA. The DC system is...
