Navyguy - derating for overcurrent protection coordination is a new one to me, is there reference to this in the CEC? Do you have any more info on it? thanks.
The easiest/most common example I can use is when doing your splitter calculations. There are circumstances when you will derate (oversize) wire and other components to allow for the proper fuse selection/coordination. This has consequences right back to the service entrance possibly.
Other examples (not so common) will be for specialized equipment and high frequency items to allow for better conductor cooling with unique fuse requirements.
Hope this was helpful..