I have been trying to tease apart the history and evolution of arc fault circuit interrupter requirements, and in the process, came across a curious historical sidenote early in its genesis, namely that the use of a 5x-or-so (IEC "B" curve) magnetic trip on general branch circuit breakers is said to serve as a highly effective fire prevention means. This was followed up on by EIA with a proposal in the 1996 NEC, but according to a UL whitepaper, the proposal was rejected due to concerns about inrush from tungsten and motor loads. However, according to this article, said IEC "B" curve breakers are considered "generally suitable for domestic applications" in at least some countries utilizing IEC-derived wiring standards, with "C" curve breakers (8x-10x magnetic trip) reserved for dedicated motor loads or other high-inrush situations (such as magnetic LV lighting transformers) in the domestic context.
This raises a question, though: why is it that the North American market seems unable to utilize magnetic trip thresholds below 7x-10x (roughly "C" curve, and generally equivalent to a QO's magnetic trip, at least on 15/20A single pole breakers)? Is it simply a matter of "half the voltage = twice the motor inrush," or is there some deeper reason that domestic motorized appliances made for the rest of the planet have a lower inrush current than their North American counterparts?
