Single dwelling neutral calculation, optional method...

[ToolHound]

I am working on a 'Neutral Calculation' Problem from
Mike Holt NEC Exam Preparation book (2008), Pg. 267.

The problem uses the 'optional method' for the single dwelling given (optional methed found in Article 220, Roman Numeral IV, starting with 220.80 and continuting with subsequent subsections of the 'optional method' for 'feeder and service load calculations').

I have attached a jpeg copy/scan of the page. Oh well, the upload snagged to a halt. Will hae to type in and upload later.

But the crux of my question is...

---Why in the solution given in the book was the 220.61(B)(1) 70% demand factor not applied in the neutral calculation ?

---And for the ungrounded conductors sizing: in light of the loads that are given for the single dwelling, how is the given 2/0 size of the ungrounded conductors arrived at ( cuz my math comes up with 130 Amps total load, which would lead to 1 AWG ungrounded conductors [either from Table 310.15.(B)(6) or from Table 310.16 ( and I don't understand why the book uses the Table 310.16 table for the ungrounded conductors of this problem anyhow. It would seem Table 310.15(B)(6) would apply, because the electrical system concerned is given to be a 'single dwelling'. )] ).

Any comment welcome. What am I missing? Thanks. ToolHound.

 

[ToolHound]

Single dwelling neutral calculation, optional method... Solution page attached.

Single dwelling neutral calculation, optional method... Solution page attached.

Single dwelling neutral calculation, optional method. Solution page attached below this post.

I am working on a 'Neutral Calculation' Problem from
Mike Holt NEC Exam Preparation book (2008), Pg. 267.

The problem uses the 'optional method' for the given single dwelling scenario

(optional methed starting with 220.80 and continuting with subsequent subsections of the 'optional method' for 'feeder and service load calculations').

I have attached a jpeg copy/scan of the book page, which includes solution to problem.

The crux of my question is...

---Why in the solution given in the book was the 220.61(B)(1) 70% demand factor not applied in the neutral calculation ?

---And for the ungrounded conductors sizing. . .: in light of the loads that are given in the book for the single dwelling, how is the given 2/0 size of the ungrounded conductors arrived at ?

( here's my math: water heater 4500 VA + electric heater 9000 VA + 17,650 VA other loads given seems to lead to...130 Amp total load. my math comes up with 130 Amps total load, which would lead to 1 AWG ungrounded conductors [either from Table 310.15.(B)(6) or from Table 310.16 ( and I don't understand why the book uses the Table 310.16 table for the ungrounded conductors of this problem anyhow. It would seem Table 310.15(B)(6) would apply, because the electrical system concerned is given to be a 'single dwelling'. )] ).

Any comment welcome. What am I missing? Thanks.
--ToolHound.


( Solution page attached down below )


​

 

[Dennis Alwon]

My understanding is that 220.61 is only for ranges. If the service or feeder fed nothing but ranges then I think you can use 70%

 

[ToolHound]

Thanks.

Thanks.

My understanding is that 220.61 is only for ranges. If the service or feeder fed nothing but ranges then I think you can use 70%

Mr. Alwon, thanks. That the 70% demand factor is for unbalanced load of just the ranges & related cooking units (and dryers too I think. Per 220.61(B)(1) ), and not for the unbalanced load of the whole entire dwelling, has rocked my (mis-)understanding of the subject. Better now than later I guess. Thanks for the insight/information. You put up with your post an attachment of a more readable copy of the book's page/calculation. Hat's off to you. --ToolHound.

 

[Dennis Alwon]

I scanned it then brought it into photoshop and cut all the excess out and enlarged it a bit