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Old 01-27-2008, 11:01 AM   #16
UAW SKILLED TRADES
 
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Hello NAP

BTW welcome to the forum it is good to have another knowledgable tradesman replying here.

I was actually directing my post to Norcal . But I'm glad you responded just the same.

This 250.122(B) thing has been a long a standing discussion of confusion and has undergone I believe 3 language changes since 1999. In 1999 it read "might need to be." and then in 2002 I believe it changed to "shall be." It currently has been commented on in the latest ROP by the code making panel for that section.
There really is no technical reason or rationale to to increase the size of the egc in typical everyday situations involving cables. Without going into all that and the math involved the section 250.122(b) is awkwardly (IMO) trying to address the possibility in extremely long runs where the egc installed with individual conductors whose upsizing to address such things as voltage drop or other adjustments increases the available fault current that can be imposed by the phase conductors on the smaller egc and considering that a larger breaker may be installed some day. Liken it to a supply water pipe being increased in size to a tank and not the drain. The water will overflow the tank because the drain cannot handle the infow.
So this section of code is concerned with fault currents that are larger than the egc can handle in certain situations where it may actually fail or open by burning through. This generally is only a concern on long runs where the amps dumped on the egc when not upsized in proportion to the phase conductors causes too much impedance (actually resistance since impedance doesn't change over distance) on the return to the breaker panel for the ocpd to open the circuit. In simple terms too small of a wire to carry the amps over an ever increasing resistance due to a long run for the breaker to see enough fault current to open.
You found out as I have that some people fail to see the logic of table 250.122 and how it applies to that section of code 250.122(B). And when you think about it.. Cables would be pretty much useless to us if we applied that code section once we get above 10 awg cables.
My point with the 40 amp breaker was simply to say that if I changed the load requiring a larger breaker what magically makes my #10 ground wire suddenly ok and not ok on a 30 since I am using a cable and I have no means to upsize the ground wire and the fact that both a #10 cable and a #8 cable have the same size ground wire.. I also see your point with the 50 amp and in hind sight I suppose would have been a better example. But at 3 in the morning my brain does not always function at 100%..... at least not since I retired and got off the red eye shift.

It is my understanding that this whole deal is going to undergo a new language change if not in this upcoming code cycle but in the next one.

Anyway your reply pretty much parallels how I would have answered those questions. So I would say we are in agreement. MY issue with this was the response to 250.122(B) by norcal that you have to upsize cause you have to and no explanation other than to say because the egc is to small. Since you responded with very close to the same argument I would have... I stayed out of that fray. I've waged it more than once.


Last edited by Stubbie; 01-29-2008 at 10:38 PM. Reason: clarification added
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Old 01-27-2008, 11:18 AM   #17
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thanks stubbie. I appreciate the supporting comments not that they are always earned though. I do have respect for you and your knowledge as you have posted very specific answers that deal with theory that I either do not prefer to delve into or may not understand nearly as well as you do so I tend to defer to your info often. You do a great job of providing complete reasoning for many situations which does allow for all to learn from your posts.

Keep it up.
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Old 01-27-2008, 11:46 AM   #18
UAW SKILLED TRADES
 
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Yes theory really is better left to the fellows over at Mike Holt they seem to host discussions quite often among other professionals on theories. In a DIY format it really can get off base and irrelevant and usually develops into a "I know more than you" ego hunt.
We all put our pants on the same and we all have or limitations in what we have knowledge. So arguments over theory have little place in a diy forum and are counterproductive unless the op is asking specifically for a theory response. I'm glad you avoid them... that is wise.
We could have dragged that upsizing deal on for a long time and believe me there are those who love to talk code. It is almost a game for some. Sort of reminds me of the bible and how everybody sees something different in the intended language...
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Old 01-27-2008, 07:00 PM   #19
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Whoa,you guys are confuuuusing.All I know is every wire in my house is #12 or larger,except for actual wires in the cans.Maybe its a waste of money but Ive only used 7 -1000 ft.rolls.lol
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Old 01-28-2008, 01:10 AM   #20
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What NAP and I are discussing has nothing to do directly with your 8/2 G. What you have done is fine.

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