Neher-McGrath Paper

The NM paper is AIEE Paper 57-660 It is in the journals of the American Electrical Engineering Institute, as I recall. This is now called the IEEE. Try your local university library, IEEE, or

In the circular file under his desk.

With emissitivity = .2 (allowed by the NM paper) and using a lay factor 1.02 multiplier (allowed by NM paper) for the rdc resistance of 203.4 microhms I = 206 amperes. This is for one conductor in free air, XHHW size No. 2 copper. Table 310.17 gives a free air ampacity of 190 amperes, but the table lists several insulations for this. It is my guess is that the minimum for all the listed insulations rounded off to the nearest 5 amperes is 190 amperes. Additionally, Table 310.17 was not derived using the NM equation, but probably was extrapolated using the values found in Table 310.16 using the equation found in the 1938 Rosch Paper.