Just to throw in the problem I have had (6 Times). If an incandescent bulb is "Banged" hard enough to short out the leads inside the bulb, the internal fuse in the bulb blows, preventing a major short. Unfortunately, the surge of current at the moment the actual "Short" occurs IS enough to fry a lamp module. Heat sinking will not help this. I have replaced the triac in a couple of modules with a higher surge-rated part, but then blew one of those on a 150 Watt flood when I dropped that. (My bad.)
I haven't actually tried a Fast-acting fuse, but I wonder if even that would be fast enough to beat the internal triac fry?
I'm only even mentioning this because I have blown so many this way, and it isn't X-10's fault in any way. The rating of the module really doesn't help in this situation either, though as was said above, for reliability, derate.
Note to Tech Types: Increasing the inductance of the coil in the module had no effect on how easy it was to blow out?
Could this mean the parts were just that sensitive to surge loads. (I must admitt, these specific modules are OLD compared to what most people would have now. (Purchased in early 80's)