Trying to understand load calculations

[blicken]

Yo, I got 5 years of calculus, down, but this electrician math is absolutely mental.
I got a book, and I'm trying to study the calculations for range demand load.
there are 3 ranges in the question, 12KW,19KW, 20KW, I want to calculate the Line and Neutral loads.
So I'm looking at Table 220.55(C)Note 2, and I see it says sum, and average the loads, OK thats 51/3 = 17KW
17KW is 5KW over 12KW, so I multiply 5*5%, to get 25%
Then it starts getting confusing: The book comes up with 14KVA from somewhere, and uses that as a multiplyer fro demand.
I have no clue how they got from 17KW to 14KVA to then use that as some demand calculation.
Can I get a code reference?

 

[Jpflex]

NEC does not explain properly, you’ll need other helpful material

 

[david luchini]

Then it starts getting confusing: The book comes up with 14KVA from somewhere, and uses that as a multiplyer fro demand.
I have no clue how they got from 17KW to 14KVA to then use that as some demand calculation.
Can I get a code reference?

Table 250.55, Column C. The demand for 3 ranges is 14kW.

 

[Dennis Alwon]

Yo, I got 5 years of calculus, down, but this electrician math is absolutely mental.
I got a book, and I'm trying to study the calculations for range demand load.
there are 3 ranges in the question, 12KW,19KW, 20KW, I want to calculate the Line and Neutral loads.
So I'm looking at Table 220.55(C)Note 2, and I see it says sum, and average the loads, OK thats 51/3 = 17KW
17KW is 5KW over 12KW, so I multiply 5*5%, to get 25%
Then it starts getting confusing: The book comes up with 14KVA from somewhere, and uses that as a multiplyer fro demand.
I have no clue how they got from 17KW to 14KVA to then use that as some demand calculation.
Can I get a code reference?

Basically you use the demand of 14kw from column C in T 220.55. From there you multiply your 25% then add to the 14kw. Ijust use 1.25 x 14kw= 17.5 kw

 

[Dennis Alwon]

Are these residential ranges? Is so then you have 70% for the neutral load

(B) Permitted Reductions. A service or feeder supplying the
following loads shall be permitted to have an additional
demand factor of 70 percent applied to the amount in
220.61(B)(1) or portion of the amount in 220.61(B)(2) determined
by the following basic calculations:
(1) A feeder or service supplying household electric ranges,
wall-mounted ovens, counter-mounted cooking units, and
electric dryers, where the maximum unbalanced load has
been determined in accordance with Table 220.55 for
ranges and Table 220.54 for dryers
(2) That portion of the unbalanced load in excess of
200 amperes where the feeder or service is supplied from
a 3-wire dc or single-phase ac system; or a 4-wire, 3-phase
system; or a 3-wire, 2-phase system; or a 5-wire, 2-phase
system

 

[Rick 0920]

Yo, sounds like you got it!