wall oven breaker sizing

[hhsting]

I have 240V, 8000va wall oven in residential townhome. The engineer has provided 50A breaker but from what I am getting is 33.33Ax1.25=41.677A so 45A breaker. Should breaker be 45A, 50A or 45A?

What size breaker should be provided NEC 2017?

 

[infinity]

Should be a 40 amp circuit. 8000/240 = 33.3 amps.

 

[hhsting]

Should be a 40 amp circuit. 8000/240 = 33.3 amps.

I dont follow. Full load amps is 33.3A but if its continuous then it comes to 45A. If non continuous then 35A breaker next standard size is 35A from 33.3A. How you get 40A???

 

[infinity]

I dont follow. Full load amps is 33.3A but if its continuous then it comes to 45A. If non continuous then 35A breaker next standard size is 35A from 33.3A. How you get 40A???

A wall oven is not a continuous load. For 33 amps you'll need #8 conductors so 35 or 40 amps will work.

 

[wwhitney]

But 50A is OK, assuming the conductors are sized appropriately:

220.55 Note 4 says to use nameplate rating for a single wall oven, so 33.33A. 422.11(E)(3) says OCPD not more than 150% of the nameplate rating, rounded up to the next standard size if non-standard. 33.33*1.5 = 50A, a standard size, so that's the largest OCPD allowed.

Cheers, Wayne

 

[infinity]

Yes with the up to 150% maximum OCPD you can use any size circuit from 35 to 50 amps. Depending on the wiring method you may be able to use # 8 for any of those 4 sizes. NM cable and 50 amps will require #6's.

 

[TX+ MASTER#4544]

2023 NEC
It's not considered to be continuous duty.

Check out Section 210.19(C). 8,750 watts....... 8,750/ 240 = 36 amps, use a 40 amp CB.
40A CB is maximum.

Use a standard size 35 amp CB and if does trip use a 40 A CB.

Thanks for reading
Comments accepted
TX+MASTER#4544

 

[TX+ MASTER#4544]

But 50A is OK, assuming the conductors are sized appropriately:

220.55 Note 4 says to use nameplate rating for a single wall oven, so 33.33A. 422.11(E)(3) says OCPD not more than 150% of the nameplate rating, rounded up to the next standard size if non-standard. 33.33*1.5 = 50A, a standard size, so that's the largest OCPD allowed.

Cheers, Wayne

2023 NEC
50 amp is to high.
Table 240.6(A) Standard ampere ratings have a 35, 40 and a 45.
If this is romex wiring then you will use T.310.16 and you will use the 60 degree terminal column for ampacity.
An 8 AWG copper type NM ampacity is rated 40 amps in T.310.16.

Thanks for reading
Comments accepted
TX+MASTER#4544

Oh, and cheers to you, wwhitney
Senior Member

 

[wwhitney]

2023 NEC
50 amp is to high.

You have not provided a reference to any NEC section that 50A would violate.

Cheers, Wayne

 

[hhsting]

2023 NEC
It's not considered to be continuous duty.

Check out Section 210.19(C). 8,750 watts....... 8,750/ 240 = 36 amps, use a 40 amp CB.
40A CB is maximum.

Use a standard size 35 amp CB and if does trip use a 40 A CB.

Thanks for reading
Comments accepted
TX+MASTER#4544

I dont follow. My range is 8000VA not 8750VA. How did you get 8750va? Also NEC 2023 Article 210.19(C) is same as NEC 2017 Article 210.19(A)(3). I dont see 40A minimum for 8000va

 

[infinity]

I dont follow. My range is 8000VA not 8750VA. How did you get 8750va? Also NEC 2023 Article 210.19(C) is same as NEC 2017 Article 210.19(A)(3). I dont see 40A minimum for 8000va

The 40 amp minimum size branch circuit is for 8.75 Kw and up so that doesn't apply to your wall oven. Be careful with the type of appliance you're referring to. A wall oven (post #1) and a range (post #10) use different methods to calculate the branch circuit size.

 

[kwired]

2023 NEC
50 amp is to high.
Table 240.6(A) Standard ampere ratings have a 35, 40 and a 45.
If this is romex wiring then you will use T.310.16 and you will use the 60 degree terminal column for ampacity.
An 8 AWG copper type NM ampacity is rated 40 amps in T.310.16.

Thanks for reading
Comments accepted
TX+MASTER#4544

Oh, and cheers to you, wwhitney
Senior Member

You apparently missed this part

422.11(E)(3) says OCPD not more than 150% of the nameplate rating, rounded up to the next standard size

Yes to 40 amp being max for 8 AWG if it is 60C conductor though which NM cable would be.