From what I can see the paragraph you reference is unchanged in 2005 (and 2002). Is there a typo in your reference? All this says is that you have to use the worst-case ampacity if you come up with two different values from NEC tables or calculations, you have to use the worst-case, subject to the exception given below.
Thank you everyone for your response. I agree it is common sense, but I need to know what was the thinking or reason in the industry to have this Article added. i.e.there could have been an accident in the industry due to an engineer choosing the highest ampacity for multiple installations, so NFPA added this to prevent future problems. I am asking this because I am trying to convince some others of this Article and how it applies to a cable installed in underground to free air(mutiple installations), in which case this Article shall determine which NEC table to use.
FWIW, this provision has been in the NEC since at least 1996. I don't know when it was added. It was not there in 1978, which is the oldest code book I have here in the office.
If you have an installation that is required to meet the NEC, then it is really not a good idea to start trying to second-guess why it says what it does. You have to meet the requirement whether you like it or not and whether or not it makes any sense. If you're trying to win an argument with an inspector, you won't.
If you really must know the origin and history, you can call the NFPA and find out what year it was added. The process for making changes in the Code is pretty open and the submitted requests for changes along with the Panel's decision and discussions are probably available from NFPA.
My guess is that this was added to make legal what any common sense interpretation would be - you need to use the worst-case. Unfortunately, there are a lot of people who make a living out of finding the loopholes and gaps in the NEC and then underbid based on cutting every corner that they know about. Pretty soon, everyone has to cut the same corners to get any work, and the NEC eventually gets "improved".
The text first shows up in 1987, but without the vertical bar indicating new material. The exception first shows up in 1990. At that point it was (c) rather than (b).
This article like all the rest are an attempt to keep down the number of insurance claims for property damage and injury. If you are looking for specific information on how to apply any article in question, the NEC Handbook is handy to have.
The best tools for understanding code changes are the ROP (report on proposals) and ROC (report on comments). These books document every code change and give a great insight on the reason for the change. The most recent ones are online at
