"There are very few situations that would fall under 'engineering supervision'."
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While the NEC contains the phrase "engineering supervision", the national building codes do not.
The national building codes including the NEC portion are simply a set of prescriptions.
You either follow the prescription or you have an engineer deviate from the prescription and stamp the plans.
Conduit fill is a prescription. An engineer can deviate from it.
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I think the above shows the legal reasoning that allows an engineer to practice engineering.
