Down sizing Neutral for Range

[jwatts]

Inspector told me he was Ok with pulling a #10 neutral for the range circuit if I could show him the exception in the code. After looking at 210.19(A)3 exception 2, that there are instances where you can downsize the neutral. However Im a bit confused on calculating the load. Do i just take 70% of the branch circuit rating? Meaning 40amps x.70=28amps? The reference to table 220.55 is what is throwing me off. The ranges are all single phase 208v on the MDU project. This inspector wants me to show him the math on any type of exceptions to the code, so I would like know if my calculations are correct before showing him.

 

[Smart $]

Inspector told me he was Ok with pulling a #10 neutral for the range circuit if I could show him the exception in the code. After looking at 210.19(A)3 exception 2, that there are instances where you can downsize the neutral. However Im a bit confused on calculating the load. Do i just take 70% of the branch circuit rating? Meaning 40amps x.70=28amps? The reference to table 220.55 is what is throwing me off. The ranges are all single phase 208v on the MDU project. This inspector wants me to show him the math on any type of exceptions to the code, so I would like know if my calculations are correct before showing him.

For one range the load per Column C, Table 220.55 is 8kW (kVA), or 38.46A, rounded to 38A per 220.5(B) at 208V. 70% of that is 26.6A, rounded to 27A. As long as your neutral conductor has an adjusted and corrected ampacity of not less than 27A, you are good to go with a 40A range branch circuit as described.

PS: Note unlike other branch circuits which conductors can be sized for the calculated load and the OCPD rating can be next standard size up under 240.4(B), range circuit [ungrounded] conductors must have an ampacity not less than the OCPD rating because 210.19(A)(3) states, "Branch circuitconductors supplying household ranges, wallmounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit..." and 210.3 states, "Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device."