Table 220.55 question

Square D

Member
Location
Tennessee
Occupation
Apprentice
Ok, this question comes from Ray Holders exam prep book-
Determine the MINIMUM size NM cable the NEC requires for branch circuit conductors, supplying a 10Kw 240 volt, single phase, residential electric range.

The provided answers in the back of the book suggests 220.55 Column B 80% to reduce the kw to 8000 Kw, then size the wire.
My question is, if Column B is for (3.5kw through 8.75 kw Rating) why choose this column when the electric range is 10,000? Thanks!!!
 

Johnhall30

Member
Location
New Orleans, LA
Occupation
Engineer
I wasnt familiar with this table prior to looking into this question, but column C suggests that if you have one appliance you can use the maximum demand of 8kw to size the branch circuit

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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes you use column C since 10kW is more than 8¾ and less that the maximum for that column of 12 kW. 210.19(A)(3) also applies but it wouldn't change the conductor size.
 

Square D

Member
Location
Tennessee
Occupation
Apprentice
Yes you use column C since 10kW is more than 8¾ and less that the maximum for that column of 12 kW. 210.19(A)(3) also applies but it wouldn't change the conductor size.
Thanks- maybe the writers didn't mean to put Column B as a code reference
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
How do you get past this when sizing conductors for a range?

(3) Household Ranges and Cooking Appliances. Branchcircuit
conductors supplying household ranges, wall-mounted
ovens, counter-mounted cooking units, and other household
cooking appliances shall have an ampacity not less than the
rating of the branch circuit and not less than the maximum
load to be served.
For ranges of 83∕4 kW or more rating, the
minimum branch-circuit rating shall be 40 amperes.

How does a demand factor affect the maximum load the range might have?
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
How do you get past this when sizing conductors for a range?



How does a demand factor affect the maximum load the range might have?
The demand factor kW value from the table is considered the maximum load served. From Note #4 to T220.50:
Note #4. Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55.
 
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