Hello: I'd like to install a GE toggle-style dimmer in a 20A circuit. My concern is that the maximum load the dimmer is rated for in a single gang setup is 600W (it is downrated for multiple gang setups). This works out to a load capacity of 5A or less, in a circuit where the overcurrent protection will happily pass 20A before tripping; or enough to fry the device at least 4 times over. I understand that the code allows fixture pigtails to be sized to the max wattage of the fixture, regardless of the ampacity of the supply, because the maximum load on the pigtail will never be more than the fixture's maximum wattage. The issue here, however, is that the dimmer feeds into 12ga house wiring, and it is possible that in the future multiple fixtures could be attached to the leg, drawing as much as 2400w! We would then have a circuit which was not fully sized to handle the load permitted by the overcurrent protection. Wouldn't this violate the code?
This is an interesting question. I suspect the real answer would be if U/L added the requirement of a fusible link in the device to blow if the allowable current was exceeded but, as far as I know it is not in the listing standard. I suspect from experience that the triac would simply short and make it a switch. Dimmers seem to fail "on".
This brings up a topic which is a pet peeve with me, inspectors who will try to enforce "idiot proofing". There is nothing in the code that I know of that requires us to go over the minimum requirements "in case" someone comes later and adds something. The "what ifs" could go on forever and my answer to them is whoever does the "what if" at a later date will be responsible for whatever is needed at that time.