Is that not part of the fault path? I also pointed it out in post 25 when I made the statement that I was not even including the impedances ahead of the circuit that would lower the current even more that would cause even longer clearing times of the OCPD.
I am by no means an expert on the math it takes to calculate all that is needed to determine the exact size EGC that will safely clear the OCPD in time to prevent conductor damage, but over the years I have seen the results of faults happening on long runs that would not clear a fault but instead cause the wire to burn or at least damage the insulation if the OCPD did finely open, the problem was many of us myself included would just attributed it to a bad or stubborn breaker that would not open or just took too long to do so, I had always known that resistance is current limiting but back then I didn't have a clue about breaker tripping curves and how current affected the clearing times making it dangerous when it took to long to clear the fault in the mid part of the tripping curves.
From the above I wanted the truth behind it and sought out the correct answers, what I found was many different answers with some being correct and some being just ol wives tales, but I learned enough to keep the EGC large enough that there was enough head room that in most cases following 250.122(B) would keep my wires safe and I could rest at night knowing that the breaker would have a low enough impedance path on a fault that I wouldn't have to worry about my work causing a fire down the road, sure it can be an over kill in many installations and end up having larger EGC's than is needed but I had to also accept that I'm not a math master and adding another long and very hard calculation to my work was not in my interest, guess in a way you could say I was being lazy and just let 250.122(B) be the guide I would use even if it was an over kill, if someone could post a better way and get it past the code making panel I would be all behind it in a heart beat, but it better be correct to the point that it will keep the wire protected as I would not want to be behind a method that may work for some but be so hard to calculate that many would not do it.
When I myself tried to find an easier method, I found like the weather there are so many variables that can't always be counted for that can cause a problem in finding the right size EGC, here are just some of these:
Quality of the insulation used on todays conductors coming from third world manufactures that we do not always have the information about what we are getting other then they are 90?c rated, it may pass UL's requirements for a 90?c rating but what if the insulation chemical formula rapidly fails at 120?c and above, I have seen 150?c rated conductors in UL listed light fixtures have the insulation melt just from the heat of the lamps that were manufactured in a third world country but they were UL listed and I did send UL a sample and they did officially list them.
Ambient temperature of the conductors at the time of the fault, which can be a big variable depending upon where a person is doing the work and the temperature changes the conductor may face in their intended installation.
Damage to the insulation at a later time that could make it easier to cause insulation failure when the fault event takes place.
I'm sure we could add to this list but after working two doubles in a row it's a little hard to get the ol mind to work any harder right now.
but if we look at all the variables that can affect the fault handling capabilities of a conductor we can kind of see why the CMP's took a very conservative approach to the sizing of EGC's on long runs, mainly because there is no one size fit's all.
So until a better way is found that is as safe I will keep up sizing my EGC's proportionately to the up sizing of my ungrounded conductors on voltage drop issues.
