cabinet-mounted oven overcurrent protection

[Wiggy333]

For some reason, I'm blocked on this. I need to know the minimum branch-circuit overcurrent protection for a single cabinet-mounted oven with a nameplate rating of 8kW/230 volts.

As near as I can figure using Table 220.19 Note 4 and some basic calculations. 8000/230 = 34.7 amperes, the minimum wire size would be #8 AWG copper (50 Amps)and the overcurrent device would be 40 amperes.

Based on the restrictions of 240.4(D) on #10 AWG (30 amps O/C) and the requirements of Table 210.24 and the language of 210.23 (B) and (C) this seems logical.

Do I now have to use the Demand Factors in Column B of Table 220.19 as noted in Note 3?

8000 x 80% = 6400/230 = 27.8 amp which would allow #10 AWG/30 amp O/C.

 

[Dennis Alwon]

You can use the demand of col. B so 10 wire would be okay but the oven usually has a nameplate rating that will tell you what size to use. Most standard single ovens use #10 on a 30 amp breaker but the newer fancier models require a #8.

 

[LarryFine]

I'd go with the #8 and 40a breaker because this oven may not last forever.