The NEC Handbook will sometimes explain some things but it is not considered an official interpretation. Sometimes the Analysis of the Changes books will have some information also. You can also read the ROP's (report on proposals) for information on why some changes are approved and some are not. Other than that I have no advice except doing what you are doing (asking questions)
I am not really certain what you are looking for or if the Code Handbookwould be of any help. Of course Mike Holt, James Stallcup and others have some good books. A good basic approach to understanding the rationale is to realize that in order for an electrical system to be safe it needs to keep potentials to ground at a minimum to prevent shock and provide current paths large enough and mechanically secure enough for the maximum available fault current to cause activation of a protective device without catastrophic damage any where in the system. Good grounding provides some of both those needs. When you are curious about a requirement, ask yourself: If this is not accomplished and a ground or phase to phase short occurred that involved this equipment, what would happen. Like Mr. Keis said in another forum, "when electricity becomes visible we are in deep trouble." Speaking of visible electricity: do you know how the requirements for 110-26(a)(1), Depth of working space and 110-26(c), Access and entrance to working space is related to fault currents?
Hmmmmm, ROP's? sounds like good reading...is this available to the average sparky? , Yes once in a while during a code update we are given books that elaborate on a code's changes, but just for that cycle. I have been collecting old code books for a while in an effort to understand how any given code would have "evolved", ( i have a prized '56), but some codes are very hard to track in that manner. As for 110-26, this is hard to own up to on line, as an apprentice, we came on an industrial job one morning to find all the lights were out, so the boss had me run up to the electrical room where a 3ph transformer fed by 480, 70 a breaker had tripped, which i found via flashlight only. Thinking only of getting on with the day's doings, and not why it might have tripped, i naively reset it. There was an audible , as well as very visual blast , the immediate result reading like 110-26-c ex#1, where my only concern was "continuous and unobstructed way of exit travel" I was lucky enough to simply end up with a temporary eye problem, and some bona-fide respect for what i was messing with.......to this day i will activate circuits only at arm's length, and never directly face such....
Wow, the motherload! recommendations, substantiation,even the situations leading to the request ( I just had to view 110-26 ,I quess I'm not the only sparky to have a bad day in an electrical room ),panel actions...drafts available for view/comment....even the 1881 one page code! This'll keep me busy for a while....Thank you Bill
Re: Code Rationale#177 12/18/0007:47 AM12/18/0007:47 AM