Simple Wall Oven Question

infinity

infinity

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Q. An 240 volt electric wall oven has a KW rating of 7.2 Kw. What is the minimum branch circuit size permitted when used on a 120/240 volt system?

a) 25 amps
b) 30 amps
c) 50 amps
d) 35 amps
e) 40 amps
 
Not sure about the intricacies of appliances, but 7,200/240 = 30, and ovens can certainly be used for more than 3 hours, so 30/.8 = 37.5. My vote is for 40 amps, and size the conductors accordingly.
 
gadfly56 said:
Not sure about the intricacies of appliances, but 7,200/240 = 30, and ovens can certainly be used for more than 3 hours, so 30/.8 = 37.5. My vote is for 40 amps, and size the conductors accordingly.
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They may be used for more than three hours, but will never continuously draw current for those three.


eta: still would be inclined to the 40.
 
gadfly56 said:
Not sure about the intricacies of appliances, but 7,200/240 = 30, and ovens can certainly be used for more than 3 hours, so 30/.8 = 37.5. My vote is for 40 amps, and size the conductors accordingly.
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Is an oven listed as a continuous load? I believe this has been discussed at length here before and was over all thought to be non-continuous, so no load adjustment needed.
Most ovens after the pre-heat time will cycle on and off thus not a continuous load.
 
infinity said:
Yes definitely not a continuous load. What about Table 220.55?
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In my opinion that table is just for calculating the service and feeder loads and is not used to size the branch circuit. I would not have any issue with a 30 amp branch circuit.
 
I think there is a note under table that says use name plate for branch circuit.

Also 2023 GFCI protection

Edit. Typed same time.
 
Here's a funny observation on 2020 NEC 220.55: say I have a 4.5 kW oven and a 4.5 kW cooktop on single branch circuit. Per Note 4, for branch circuit sizing, I treat that as a single 9.0 kW range, and Column C Row 1 tells me that the branch circuit needs to be sized at 8 kW, or 33.3A, so a minimum 35A OCPD.

But on the feeder supplying that OCPD, Note 3 says the load calculation may use Column B Row 2, a 65% demand factor, so the feeder load is 9.0 kW * 65% / 240V = 24.4A.

Is there anything else in the NEC that would prohibit having a 25A OCPD supplying a feeder to a 35A OCPD supplying a branch circuit supplying the 4.5 kW oven and 4.5 kW cooktop?

Cheers, Wayne
 
augie47 said:
'23 Code appears to have reduced the controversy with a Note 5 stating the branch circuit shall be rated per the nameplate.
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Thanks since were still under the 2020 the question in the OP was in regard to that. I see that the T220.55 notes in the 2023 have changed slightly with the changing of Note 5 and moving some of the wording of Note 4 to Note 6.

Summary:
Under the 2020 a single range may use T220.55 but a single wall-mounted oven or counter-mounter cooking unit cannot use T220.55 to size the branch circuit.
Under the 2023 nothing has really changed regarding this question except for the rearrangement of the wording of the notes.

So back to the OP since this is a wall oven the branch circuit is sized according to the nameplate rating of the wall oven without using the demand factor from T220.55. If the question used a range instead of a wall oven then the demand factor of 80% (single range between 3½-8¾ kw) from T220.55 can be applied.

2020 NEC:

Note:
4. Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.

2023 NEC:

Note:
4. Calculating the branch-circuit load for one range in accordance with Table 220.55 shall be permitted.
5. The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance.
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infinity said:
Simple Wall Oven Question
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crackup.gif
 
Last edited:
infinity said:
Thanks since were still under the 2020 the question in the OP was in regard to that. I see that the T220.55 notes in the 2023 have changed slightly with the changing of Note 5 and moving some of the wording of Note 4 to Note 6.

Summary:
Under the 2020 a single range may use T220.55 but a single wall-mounted oven or counter-mounter cooking unit cannot use T220.55 to size the branch circuit.
Under the 2023 nothing has really changed regarding this question except for the rearrangement of the wording of the notes.

So back to the OP since this is a wall oven the branch circuit is sized according to the nameplate rating of the wall oven without using the demand factor from T220.55. If the question used a range instead of a wall oven then the demand factor of 80% (single range between 3½-8¾ kw) from T220.55 can be applied.
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Does that mean table 250.55 can be used for range branch circuits or is it implying that the circuit supplying the range is a feeder?

P.S. I would have chosen 40A as well. But that is because I am always afraid to undersize circuits with heating elements.
 
infinity said:
So back to the OP since this is a wall oven the branch circuit is sized according to the nameplate rating of the wall oven without using the demand factor from T220.55. If the question used a range instead of a wall oven then the demand factor of 80% (single range between 3½-8¾ kw) from T220.55 can be applied.
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OK, but in either case the feeder supplying the branch circuit can use the 80% demand factor. So which NEC section, if any, does providing a 25A feeder to a 30A branch circuit for the 7.2 kW oven violate?

Cheers, Wayne
 
wwhitney said:
OK, but in either case the feeder supplying the branch circuit can use the 80% demand factor. So which NEC section, if any, does providing a 25A feeder to a 30A branch circuit for the 7.2 kW oven violate?

Cheers, Wayne
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You got me because that makes little sense with regards to the feeder. This is only about the branch circuit but I see your point.
 
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