Sizing wall oven/ranges

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Janutolo80

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Am I correct by saying table 220.55 is just for service calculations? And when you size the wire and breaker of the appliance is based on the name plate and not the demand factor? ie., a wall oven that pulls 45kw’s would need to still be sized based on the name plate with #10 or #12 at 18 amps and breaker sized to 80% with a 30amp double pole?
 
Welcome to the forum!

Table 220.55 does not apply to branch circuits. An oven that pulls 45 kW is more of a room oven than a wall oven. Did you mean 4.5 kW? That would draw 18.75 A and require #10 wire with a 30/2 breaker.
 
JoeStillman said:
Welcome to the forum!

Table 220.55 does not apply to branch circuits. An oven that pulls 45 kW is more of a room oven than a wall oven. Did you mean 4.5 kW? That would draw 18.75 A and require #10 wire with a 30/2 breaker.
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Yes, 4.5kw. Why couldn’t you use #12 NM?
 
A 20 amp circuit is permitted with #12 conductors because it is not a continuous load. T220.55 can be used to size the branch circuit when applicable. See note 4 of that table.
 
retirede said:
For sizing the branch circuit, there should be an amp rating on the nameplate. The 4.5 KW is likely just the element.
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The name plate is listed at 120/240 4.5 kW no mention of anything else. I agree needs to be 30 amp breaker and I’d rather use #10 but if #12 NM is good for up to 20 amps wouldn’t that be permissible?
 
Janutolo80 said:
The name plate is listed at 120/240 4.5 kW no mention of anything else. I agree needs to be 30 amp breaker and I’d rather use #10 but if #12 NM is good for up to 20 amps wouldn’t that be permissible?
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Are you using a 20 amp OCPD? Then #12 is fine.
 
Manufacture wants it on a 20 but at 18 amps that’s contrary to sizing circuits to 80%. Imo it needs to be on a 30. They ran #8 AL and put it on a 40 amp breaker.
 
Janutolo80 said:
The name plate is listed at 120/240 4.5 kW no mention of anything else. I agree needs to be 30 amp breaker and I’d rather use #10 but if #12 NM is good for up to 20 amps wouldn’t that be permissible?
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Because #12 is required to be protected at 20A in this case.
 
I am also looking at specs for a 4.5kw wall oven. The specs call for a 240 Volt, 20 Amp circuit. I wasn't going off the 220 section of the code, but more 210.19C which states the appliance shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. It does not seem to mention continuous or non continuous at all in that article. I generally would go by the 80% rule for a breaker. Maybe for cooking appliances it is noted somewhere else in the code? I would think that at times a oven could be on for over 3 hours.
 
JoninCO said:
I am also looking at specs for a 4.5kw wall oven. The specs call for a 240 Volt, 20 Amp circuit. I wasn't going off the 220 section of the code, but more 210.19C which states the appliance shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. It does not seem to mention continuous or non continuous at all in that article. I generally would go by the 80% rule for a breaker. Maybe for cooking appliances it is noted somewhere else in the code? I would think that at times a oven could be on for over 3 hours.
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The oven can be on for 3 hours but not at full current. The thermostat kicks it on/off to adj the temp. A continuous load is full current for 3 hrs or more.
 
Janutolo80 said:
So because it’s non continuous size at 100%? 18 amp load on #12 and a double 20?
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Yes that's correct. A 20 amp individual branch circuit can be loaded to 20 amps {210.22} and since this is a non-continuous load it can be on a 20 amp circuit. The 80% factor would apply if this were a continuous load but as Bill outlined it does not meet the Article 100 definition of a continuous load.

210.22 Permissible Loads, Individual Branch Circuits.
An individual branch circuit shall be permitted to supply any load for which it is rated, but in no case shall the load exceed the branch-circuit ampere rating.
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Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.
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