Range Calculations

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rustyhd

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One wall mounted 2.75kw 220 volt wall oven is to be wired on a separate dedicated ? What size OCP is required? What size branch circuit conductors need to be used? I come up with 15 amp OCPD on 14 AWG.
But my instructor say that it should be on a 20amp OCPD on 12 AWG.
Witch one is right? and is there a code ref. for this:-?
 
This one could go either way. I think it hinges on whether we are to consider a wall mounted oven a ?continuous load.? If so, then 210.20(A) would require an overcurrent device rated no less than 15.6 amps (i.e., 2750 watts divided by 220 volts times 125%). That would make the instructor?s answer correct. If a wall oven is not considered ?continuous,? then the 125% factor is not needed, and that would make your answer correct.

I side with you. It might take more than three hours (the definition of ?continuous?) to cook a meal. But the oven will cycle on and off during that time, so that does not meet the definition of ?continuous.? So unless there is a specific rule that says oven are to be treated as ?continuous loads,? and I am sure someone will report the fact if I turn out to be wrong, then I would give the same answer you did.

Welcome to the forum.
 
Hi Charles
thanks for the input I see where 210.19 (A)(3) Exception No. 1:
Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units
shall have an ampacity of not less than 20 amperes and shall be suffıcient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance. could this be where the 20amp OCPD is coming in to play? man-o-man sum times the code book can give you a headache
 
rustyhd said:
Hi Charles
thanks for the input I see where 210.19 (A)(3) Exception No. 1:
Conductors tapped from a 50-ampere branch circuit supplying electric ranges, wall-mounted electric ovens, and counter-mounted electric cooking units
shall have an ampacity of not less than 20 amperes and shall be suffıcient for the load to be served. These tap conductors include any conductors that are a part of the leads supplied with the appliance that are smaller than the branch-circuit conductors. The taps shall not be longer than necessary for servicing the appliance. could this be where the 20amp OCPD is coming in to play? man-o-man sum times the code book can give you a headache
Click to expand...

If you're tapping into a circuit then it's not dedicated. Dedicated circuit = intended for one single piece of equipment and nothing else. I think the main text of 210.19(A)(3) applies to you, not the exception... but of course, under that reasoning, your "load to be served" is 12.5 amps. Like charlie said, if it's continuous (which it's probably not; it's unlikely you're going to run the thing full-bore for 3 hours), then you'd have to calculate your load at 125% for the OCPD but otherwise I'd say the 15 amp circuit would do it.
 
250.55 (Table) note No.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.

note the word shall in second sentence.
 
cpal said:
250.55 (Table) note No.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.

note the word shall in second sentence.
Click to expand...

I was gonna say "because table 220.55 is for service or feeder demand," but then I saw your mention of Note 4. I don't think I had ever read Note 4 :roll:

Well, I learned something today. *shuts brain down till tomorrow*
 
I'm curious about your using 220 volts in the calculation. IMO the unit should be marked 208 volts or 240 volts. If the unit is marked 240 volts and your applied voltage is only 220 volts the output and current values will be lower than if the unit were operating on 240 volts.
 
ibew501ed said:
yes I've read note 4 and thats why I agree. However I question why they list 1 appliance under colA if you cant really use it . can you think of an example where col A is used for 1 appliance?
Click to expand...

This is from the handbook (NEC)
"The demand factors in the Code are based on the diversified use of household appliances, because it is unlikely that all appliances will be used simultaneously or that all cooking units and the oven of a range will be at maximum heat for any length of time."
Note 4 states "shall" for BC.

I think the % in Col A and B are for feeder demand where diversity is applicable.

There is a argument to be mades regarding the language of
210.19 Conductors —

Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served.
in general where a branch circuit supplies (1) appliance-household cooking Eq.) Note 4 drives the minimum capacity as stated.
 
ericsherman37 said:
I think it says "shall be permitted" actually. Not mandatory.
Click to expand...

The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance.

The note appears to mandator "shall be the name plate rating"
this indicates that Col A or B should not be used to calculatethe BC load. Those columns

( I believe are for feeder demand)
 
cpal said:
The branch-circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance.

The note appears to mandator "shall be the name plate rating"
this indicates that Col A or B should not be used to calculatethe BC load. Those columns

( I believe are for feeder demand)
Click to expand...

I see now :D Table 220.55 may be used for the branch circuit calculation of a single RANGE. The nameplate shall be used for calculations of wall-mounted ovens or cooktops.

Thanks for enlightening me :D
 
I would like to thanks every one for the input on this. I'm taking this up in class today and see what happens thanks for the help
 
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