Very interesting and useful articles written by Mr. Fuhr.

A few comments:

Regarding "Undersizing of Utility Main Service Transformers":

I agree that the use of the NEC results in an oversized distribution system. There are several reasons to it:

Among them, I'd like to refer to Table 220.12 of the 2008 NEC (“General Lighting Loads by Occupancy”) . The unit load values established in this Table are more than 25 years old. Since then a lot has changed regarding the use of energy. In the case of lighting, the, incandescent bulbs are replaced by CFL’s (about three times more efficient), T12 lamps are replaced by T8 and T5 lamps, and magnetic ballasts by electronic ballasts. Luminaires are more efficient and today advancement of efficient LEDs is a fact. Today's IES recommended levels of illumination are considerably lower than the ones existing in the seventies. To complete the picture, we have today the ASHRAE 90.1 standard, and buildings seeking LEED certification. Just as an example, for office buildings, the unit value established in 220.12 is 3.5VA/sq ft while the Light Power Density (LPD) allowance by ASHREI 90.1-2001 is 1.5W/sq ft for enclosed offices and 1.3 for open plan offices. Based on the above, it seems that following the requirements of Table 220.12 leads to oversizing conductors, raceways , panelboards, transformers, etc. I believe that the time is ripe to revise the requirements of Table 220.12 and adjust it to today’s reality.

There are other factors to consider: As Mr. Fuhr correctly states, the electrical design engineer depends for its load calculation on data supplied by other trades. In general, these constitutes the major portion of the load and, normally, the data supplied is conservative.

Another important reason: The electrical design engineer must abide by the NEC, which rules are much more stringent than the ones followed by the utilities. For example, NEC does allow for demand factors but not for diversity factors, while utilities, apply both.

I believe that although the service conductors sizing are the responsability of the design engineer (according to the code), the service transformer characteristics is the responsability of the utility, according to the data supplied by the design engineer and the utility's norms. The protective device coordination study can not be done at the design stage, but it's the rrisponsability of the design engineer (at the design stage) to specify OCPD with the features (long-time, short-time, instasntaneous and GFP adjustments, where applicable) that will facilitate the protection engineer to do the coordination study of the system, including the utility transformer (in coordination with the utility).

Regarding the "High Inrush Currents for Dry Type Transformers":

Mr. Fuhr's article considers only circuit breakers. From the article it can be seen that for medium size and up, the best coordination is achieved by CBs equiped with adjustable electronic trips (long-time, short-time and instantaneous). However, for smaller size transformers, it may result too expensive to use a primary transformer OCPD with these caracteristics. I think that in these cases consideration should be given to the use of dual element time-delay fuses, whose size could be about 125% of the XFMR's primary FL current, instead of using molded case breakers sized at 250%, which translates in larger size XFMR's primary feeders.

To end, may I suggest Mr. Fuhr to add to the above articles the case of GFP (where applicable), to complement the study of coordination.

Jacob Mendelovici