An engineer explained it like this: An airplane is designed to 110% of expected load. The construction is closely monitored and regular maintenance has to be done. However, buildings are designed to 200% or more of expected load. Then, if the construction crew does half a job, it will still hold up.
The electrical code is well above 100% of expected load. Look at the insulation on wire. It has a temperature rating. I'm certain that I've never felt a conductor anywhere near it's design temperature. Code minimum already provides leeway for poor installation.
Some electrical engineers spec #12 wire for fire alarms. Try pulling a device out of the box with four #12 wires on it! We (Canada) must leave 6 inches of conductor in a box. Why not improve on that and leave a couple feet? More isn't better.
The code is based on engineering and experience. Code isn't minimum. Code is simply correct.
