EGC increased in size per 250.122(B)

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You might also want to look at Volts from Dolphins Software. It does size ground conductors per 250.122 and 250.66. It also automatically upsizes the ground conductor when increasing either the conductor or the OCPD.
 
Snorks said:
You might also want to look at Volts from Dolphins Software. It does size ground conductors per 250.122 and 250.66. It also automatically upsizes the ground conductor when increasing either the conductor or the OCPD.
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That looks like it would do what I need, but I don't need everything else. It would be great if they had breakout pricing of individual modules. thanks
 
ptonsparky said:
Just about had a spreadsheet finished this morning but had to actually work today. Hate it when work gets in the way.

If you are still interested I think I have what you want. Send me a PM.
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I made one up, too. Had to jump through a lot of [Excel] hoops to get it to work, but I think I got it right now. Sent you a download link in a PM...
 
While correcting an "oops" in my spreadsheet I noticed that the max size EGC for AL is 1200 in Table 250.122. There is no 1200 in Chapter 9, table 8. It jumps to 1250. Why use 1200 when there is no cable that size? I know we could parallel but that is not consistant with the rest of the table .250.122
 
ptonsparky said:
While correcting an "oops" in my spreadsheet I noticed that the max size EGC for AL is 1200 in Table 250.122. There is no 1200 in Chapter 9, table 8. It jumps to 1250. Why use 1200 when there is no cable that size? I know we could parallel but that is not consistant with the rest of the table .250.122
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That looks like an oops to me in the table. 1200kCMIL is not in 310.16 either.

Also interesting that the CU EGC's go up with every C/B size once we hit 100amps. The AL side uses 600kCMIL and 1200 kCMIL twice
 
sandsnow said:
A big thank you to both ptonsparky & Smart $ for the calculators. Way cool!!!
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You are quite welcome! (again)

I hope you don't mind my posting, in part, a PM here, as I would like forum feedback on the issue...

sandsnow said:
Smart $ said:
sandsnow said:
Wow
That is exactly what I was looking for. This was so great of you to build that.
I can't thank you enough.
Larry
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Your quite welcome!

I have updated my calculator...

The reason for doing so was that the result was based entirely on cmil ratio of the conductor upsizing. As a result of doing it that way, when the minimum and increased conductors and EGC size was in AWG range, the calculator would yield an upsized EGC that was one size too large. For example, if the minimum conductor size was #3, the increased conductor size was #1, and the minimum EGC was #8, the calculator would return an increased EGC size of #4 (83690 ? 52620 ? 16510 = 26258, which is greater than #6 at 26240). I believe the NEC will allow upsizing by AWG. For example: #8 ? (#3 ? #1) = #6.
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I think you had it right the first time. The code does not mention anything about increase by AWG. Here's the section:

(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.

I'm not seeing where you can increase by AWG. What am I missing?

Again many thanks for your time on this.
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To which I responded:
First off it says "...according to circular mil area..." It does not say circular mil area specifically as provided in tables. It also does not provide a basis for the "according to" part... that is, it does not say you can't round down, and it does not say you have to round up.

The point I am getting at is that the cmil values provided in tables are standard but they have been rounded, some up... some down, to four significant figures. In using the ratio of two sizes and multiplying by a third to determine a fourth size, the rounding is compounded... and there are no rules for what to do when one size's cmil area has been rounded down and another's area has been rounded up.

In the end, basing the determined size on the gauge number has a deviation of less than 0.3% compared to the calculated cmil area using table values... for all possible combinations. To help you understand more completely, I have prepared an Excel worksheet showing ratios in two tables. One table is using the cmil areas using the precise values calculated with the AWG diameter formula. The second table uses table values. You can download it here.
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