I believe that engineering supervision means that a PE has stamped the plans. It doesn't mean that he has made any calculations, but he is approving the work of someone who doesn't have the PE. As Steve pointed out, the liability issue of stamping plans that aren't in compliance is huge. As far as being able to override a pertinent provision of the NEC, the NEC allows for this in 310.15.
NEC 310.15(A)(1) states:
"Tables or Engineering Supervision.
Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C). "
310.15(C) states:
"NEC 310.15(C) Engineering Supervision
Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general formula: [FORMULA]"
In Wisconsin, the derating factors do not apply to residential branch circuits.
“ARTICLE 310 – CONDUCTORS FOR GENERAL WIRING
Comm 16.30 Ampacities for conductors rated 0 – 2000 volts [NEC310.15]. (1) ADJUSTMENT FACTORS [NEC 310.15 (B)(2). This is a department exception in addition to the exceptions specified in NEC 310.15(B)(2)(a):
Exception No. 6: The derating factors shown in Table 310.15(B)(2)(a) do not apply to branch circuits supplying an individual dwelling unit.”
It appears to me that Steve is on firm ground for applying the 310.15(C) formula. If he is trying to approve something that exceeds the 310.15(C) formula, I don't think he can legally do that.
As far as overriding the NEC absent a specific provision, I don't think that's true. Of course, if the local AHJ is willing to go with it, perhaps it is acceptable.
Sounds like something a bunch of lawyers would argue over!
By the way, I am also a PE in Electrical Engineering. The biggest thing you learn being a PE is not to sign something unless you can back it up. Caution is the order of the day.
Frank
