Amp rating of dimmer switch feeding 4 luminaires

[GoldDigger]

Another thing I learned the hard way at our church is that large PAR type bulbs (100, 150W) have very heavy filaments that conduct a large arc for a brief time when they burn out. They would routinely take a 600W dimmer with them when they failed, but a 1000W dimmer is still working fine after outlasting 4 bulbs.

 

[JFletcher]

Another thing I learned the hard way at our church is that large PAR type bulbs (100, 150W) have very heavy filaments that conduct a large arc for a brief time when they burn out. They would routinely take a 600W dimmer with them when they failed, but a 1000W dimmer is still working fine after outlasting 4 bulbs.

Wow, havent seen that one. Have seen 10 bank set of can lights lamped with 100W bulbs on a 600W dimmer. Dimmer was extremely hot to the touch. When I removed the unit, I discovered it was half melted and maybe minutes away from catching fire. I replaced it and all those 25,000hr bulbs (which apparently are no longer made or imported) with standard life 40W bulbs, which put out more light anyway.

Was it basically a short circuit causing your dimmers to fail, or were they melted like mine?

 

[GoldDigger]

...
Was it basically a short circuit causing your dimmers to fail, or were they melted like mine?

They were just fine during use. It was only at end of life for a bulb that it drew a short but major overcurrent at the moment the filament failed.
You have probably noticed how sometimes an incandescent bulb will fail with a flash (especially if it happens at turn on). These bulbs did that, with a high enough current that they simply blew out the triac element(s) in the dimmer.
It was three 150W bulbs, each on its own 600W dimmer. I had to replace all three with 1000W dimmers.

 

[Electric-Light]

So the breaker is sized to protect the wire, but the switch must only be sized to safely carry the expected connected load, even if that means it's a lower continuous rating than the circuit itself is capable of safely carrying?

What if the switch is feeding a general purpose receptacle? Then mustn't the switch be rated for the full circuit rating (15A; since you can't "control" the load that someone plugs into the receptacle - whereas, conversely, luminaries are hard-wired, thus the load is essentially fixed)?

Dimmers control the entire load within the semiconductor chip and conventional wisdom that apply to passive devices do not apply. They have extremely low tolerance for impulse loading. Some dimmers are rated for incandescent as well as electronic loads. Latter have a capacitive input and have different inrush profile than incandescent hence the dimmer having 600W incandescent/150W LED ballast load.