Quick question about wattage

[tweetersaway]

I'm not all that well versed in the workings of electricity, and all this thought about using satellite dimmers got me curious. What would happen if you plugged a 1000 watt fixture into a 600 watt dimmer? Would it blow something, or would the lamp only be able to output at 60%? Not that I'm going to do this, I just think it'd be kinda interesting to know.

 

[gafftaper]

The lamp will try to draw 1000 watts of power through that circuit. However the circuit is only able to provide 600 watts of power. The end result will be a circuit breaker trips and it gets dark. If the circuit breaker didn't trip then there would be a fire. Because you are trying to pull too much power through something not rated for it and it heats up... like an electric heater.

WHAT FOLLOWS IS NOT WISE. DON'T DO IT: You could run the lamp at 50% and then it would only need 500 watts of power and the breaker "hopefully" wouldn't trip. People do crazy things like this at small theaters and churches. The danger of course is you forget, run it up too high, and the breaker trips in the middle of a show OR worse the breaker doesn't trip and you have an electrical fire.

Always be aware of the dimmer rating, the rating of the cable in the system, and the amount of wattage you are trying to plug in.

 

[LDTom]

To further the point made above and to add my 2 cents. It is very unwise to put anything on a dimmer that you know is over the limit.

600 watt dimmer, probably best if you max out with like a 500 watt lamp or a total around 500 watts on that dimmer. Now the reasoning that there is a 100 watt difference between what the dimmer can handle and the load. This is to guarantee that the dimmer would not under normal circumstances be overloaded and trip or start a fire in the dimmer rack.

I usually work with 2.4 K dimmers and the max that I put on them is 2 thousand watts and this is just a rule of thumb and is more playing it safe and taking the necessary steps to avoid a serious problem with the dimmer rack in the middle of the show.

 

[David Ashton]

You could run the lamp at 50% and then it would only need 500 watts of power

Not very accurate, sorry, but at 50% of voltage you're generally at about 80% of power due to the serious non linearity of lamp loads.

 

[rmarston]

The dimmer you refer to is rated to supply 600 watts max. So, that means it is thermal and electrically design to supply a maximum of 600 watts, furthermore it is protected by a circuit breaker or fuse which will open if the load (light) attached to the dimmer exceeds 600 watts. So a 600 watt dimmer will conservatively handle a 500 watt lamp.

 

[JD]

The reason dimmers are 600 Watt, 1.2kw, 2.4kw is a simple quirk of the math, more than a specific design safety factor.

Watts = Amps times Volts. 10 amps at 120 volts gives you 1200 watts, thus the 1.2k rating.

That being said, it does provide a nice safety area. Overloading dimmers and hoping to remember not to turn them up over 50% is real bad for a third reason, the peak inrush demand on the thrysistor occurs at the 50% setting, not the 100% setting!

At 50%, the devices are turning on at the exact peak of the ac waveform. (Dimmer curves aside.) At 100%, the devices are being turned on near the zero voltage cross, which is fairly low in current.

Fuses blow due to accumulated heat. Thrysistors (SCR, Triac, SSR, IGBT) blow due to inrush current, and may do so within the first few repetitive ac cycles.

 

[ship]

After all this scientific stuff/arguement, what happens after a 1kw load gets placed on a 600w dimmer - assuming it's an architectural dimmer we are talking about or in having seen it, your dimmer for all intensive purposes becomes a switch and stops being a dimmer.

Literally the dimmer curve just fuses and it goes off, long pause on, long pause off in having no dimming curve left after use. Not sure why in it not fusing and assuming no fuse either but I have seen many a illegal by NEC standards archithictural dimmer used in overloaded condition react in the same way.

Hope it helps in describing what happens. Dimmer toast in other than turing on and off.

In a safety sense, don't do it, what could happen for a dimmer designed for 600w is major overheating and fire. Most likely not but it's still there in opportunity in resistance causing heat before failure before it stops working properly or beyond. Little wires designed for 600w don't like 1K loads on them.

 

[JD]

Architectural dimmers are often very simple, a pot, a cap, a Diac, a Triac, and a choke. For some reason, often it is the Diac that fails, and that produced the "no curve" effect. A Diac (bilateral trigger diode) is used in a simple phase shift configuration with the cap to trigger the gate of the Triac. When it goes, so does the phase shift configuration. At that point, you are just turning up (down) the pot until you get enough current to gate the Triac, and now have a rotary wall switch!