Dan:
I am a bit confused by what you say below regarding "whim and
interpretation." In regards to the 690.64(B) 'conductor' controversy, the
controversy is not about what the code says or how AHJs interpret it, the
controversy is about why the word "conductors" is included in the NEC
section at all.
There is nothing "whim" about a local authority implementing specific
language: It is very straight-forwards: take the values of contributing
circuit breakers, total them, and the conductor must be rated equal to or
greater than 120% of the result. This is simple arithmetic and not subject
to interpretation.
What is capricious is the code authors failing to understand that applying
the 120% rule to conductors that will never see excessive currents is not
logical.
I think we should be educating the local AHJs, but all the education in the
world will not allow them to waive a very specific code requirement. It is
too much to ask them to "pull rank" on the code writers. Once they start
nit-picking code sections, they could spend most of their time trying to
figure out which code sections are really valid. Should each municipality
issue a copy of the NEC with the sections they don't agree with
redlined? This is unfair to ask of local building officials.
Instead, we need to direct our efforts to code writers in order to educate
them to understand the real scenarios, using basic physics. This is why I
support and follow Solar ABCs and pay for and attend Mr. Brooks seminars
whenever I can. These are our representatives trying to inject common
sense into the code crafting process.
I agree with you there is a problem here, I just disagree on who can make
the necessary changes.
Sincerely,
William Miller
PS: All of the above assumes that you and I are correct in our
understanding of the basic situation: a feeder conductor can never see
additive currents from power sources at opposite ends. I am not a
scientist or an electrical engineer. I have been wrong before and I am
certainly making plans to be wrong about something else in the near future.
wm
At 01:20 PM 10/1/2012, you wrote:
William,
My point exactly. Unfortunately, vocal inflection isn't easily
incorporated into typed text.
For an "advisory only" document, it has, in essence become the
"law of the land" (as we're acutely aware), however subject to
the whim and interpretation of the nationwide AHJ hierarchy and
their governing/supervisory colleagues.
Dan
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