Counting Neutral as Current Carrying Conductor

[stevee]

NEC 315.15(B)(4)(c) states that where a "MAJOR PORTION" of the load consists of non-linear load, harmonic currents are present in the neutral conductor; the neutral shall therefore be considered a current-carrying conductor.

What constitutes a "MAJOR PORTION?" I would assume that to mean more than 50%. What do you think the intention of the NEC is?

Now to make the question more confusing, which part of the load calculation are you looking at?

Say for example you are calculating feeder conductors. Your feeder demand calculation determines that you have 100,000 va of Line Power and 35,000 va of Neutral Power. If 25,000 va of the neutral load is for HID lighting (which is a non-linear load) do I have to count the neutral as a current-carrying conductor?

In other words am I comparing the non-linear load to the total line power or to the total neutral power? If using the line power I have 25,000va(HID)/100,000(total line) which means my non-linear load is only 25% of my total load. If using the neutral power I have 25,000va(HID) / 35,000va(total neutral) which calculates out to 71% of my total neutral load.

So, which is it? A major portion of the total Line Load or the total Neutral Load?

 

[charlie b]

Good question. I don't have an answer, except to say that you won't find the answer in the NEC. As a practical matter, this is one of those "Ask the AHJ" issues, for anyone else's answer is not going to fly. My own view is that I would not count the neutral in your example.