NEC ampacity tables are based on IEEE 835/1994 calculations. However, for cable tray it is not mentioned in NEC how the table here is calculated. It is not any connection with ANSI/NEMA WC1/ICEA P-54-440, for instance.
On an open delta three phase transformer in order to obtain a high leg voltage [208 V for instance] we take a full phase-let’s say a_b and a half of the other phase winding [a_n]
In my opinion, a half secondary winding transformer presents only 1/4 impedance [instead of 1/2 as it seems to be]...
Cable Ampacity in solid-bottom [metallic] open-top –usually in a power station-one could calculate it following J.Stolpe-"Ampacities for Cables in randomly filled trays"/1971way.
But in N.E.C. world it is only a tiny mention in-N.E.C. 2011-392.17(2)(c )
"Exception to (2)(3): For solid bottom...
I don't know any standard of underground laid cable ampacity calculation which would take into consideration Ground drying effect except IEC 60287-1-1.
But here is a problem. Using formula shown in 1.4.2.1 as the critical temperature rise of the soil [Dx] is added to upper part of the ratio...
In order to state, according to NEC, the cable in Embedded Duct Bank Ampacity one could encounter a problem :
For number of ducts differing from 1,3,6,9 there is no tables so you have to follow :
NEC ch. 310.10
310.15 Ampacities for Conductors Rated 0–2000 Volts.
Ampacities for conductors shall...
In a Connection Substation, 3 generators of 100 MW each and 26 step-down transformers of 20 to 40 MVA are connected .
An usual test of measuring instrument over all the Station was performed.
One of the transformer connection [40 MVA Yo/D ] shows an odd result. One of the phases was less than...
