over loading a dimmer
- Thread starter sparky333
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I have seen a 600 watt dimmer last for years with 650 watts on it before it burnt out. Generally, most dimmers won't last very long-- Lutron's , IMO have a better chance of making it.
If it were my choice I would use a 1000 watt dimmer even with 600 watts of load.
If it were my choice I would use a 1000 watt dimmer even with 600 watts of load.
There's no single answer to the OPs question. The dimmer may never fail. It may get hot to the touch, then decide to die next year. It may just quit after one day. It may operate intermittently. It may burn the house down. It might even get America to agree on the health care issue.
kwired
Electron manager
- Location
- NE Nebraska
It will be overloaded beyond the mfg rating. It will continue to work at a higher temperature until something is heated to a point of failure. How long this will take is different for every installation. If heat dissipation abilities are higher on one install vs another with everything else the same then that one should last longer.
Not likely to start a fire if installed in a box like it is supposed to be. This is the reason for requiring a box at switches. A loose terminal screw on a standard switch can also be an ignition source. But only the first couple of inches of conductor see much temp rise and is in free space within the box. usually burns itself out before raising temperature of any combustables because of the box.
broadgage
Senior Member
- Location
- London, England
An overloaded dimmer is most unlikely to catch fire, if otherwise installed correctly.
I doubt that dimmers liable to catch fire in the event of entirely forseeable user misuse would be UL listed.
If however the device was improperly installed, for example directly in a wooden wall without any backbox, then there might be risk of fire even at normal loads, and overloading would increase the risk.
An overloaded dimmer is liable to failure due to overheating of the semi-conductors or other components, this will require a new dimmer but should not be dangerous.
A good dimmer might withstand a slight overload for years, some cheap ones are not IMHO trustworthy at more than 50% of the ratting.
I doubt that dimmers liable to catch fire in the event of entirely forseeable user misuse would be UL listed.
If however the device was improperly installed, for example directly in a wooden wall without any backbox, then there might be risk of fire even at normal loads, and overloading would increase the risk.
An overloaded dimmer is liable to failure due to overheating of the semi-conductors or other components, this will require a new dimmer but should not be dangerous.
A good dimmer might withstand a slight overload for years, some cheap ones are not IMHO trustworthy at more than 50% of the ratting.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I don't worry about fires. If the unit is a Lutron then it is rated for the full 600 watts whereas, many other manufacturers derate the load to be 480 watts max. on a 600 amp dimmer. I believe the manufactures use the 80% rule to get 480 watts. Likewise the 100 watt dimmers would be rated 800 watts.
Remember this depends on the manufacturers installation instructions.
Remember this depends on the manufacturers installation instructions.
charlietuna
Senior Member
A 600 watt load on a 600 watt dimmer is poor installation practice. Yes a 1000 watt dimmer will cost a few more dollars, but it will function for ever. I use the "continuous load theory" ! Same with photo cells--disconnects -- starters -- etc..
Missing a zero disregarded, I think you mean 1000 watt dimmers should be loaded to 800 watts maximum, not rated 800. If you 'rate' them 800, then you should only load them to 640 watts.
- Location
- Massachusetts
Can someone show me anything that tells me dimmers are not designed for 100% loading?
Usually, it's my customers.
I intentionally derate dimmers solely to prevent them calling me about "hot dimmers that are going to burn my house down!!!!" I prefer to avoid the situation altogether and over-engineer.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Lutron specifically allows 100% rating of their dimmers but, if memory serves me well, the old rotary dimmers made by eagle or someoneelse would state in the instructions that the load could only be 80%. That was years ago as I can't recall the last time I installed a dimmer that was not Lutron.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It appears that the other manufacturers have it worked it. Here is a rotary from cooper
Karl H
Senior Member
- Location
- San Diego,CA
Volta
Senior Member
- Location
- Columbus, Ohio
The load calculation for the outlet supplying a luminaire should be matched to the maximum fixture rating, not the currently-in-place lamps 220.14(D).
If the customer increases the wattage of the installed lamps beyond the rating of the dimmer, then they will have exceeded the rating of the fixture too.
Philip Barr
Member
- Location
- Minneola Florida
My rule of thumb with sizing dimmers, size them according to
the largest allowable bulb for the fixtures it controls, not the bulbs you are actually installing.
the largest allowable bulb for the fixtures it controls, not the bulbs you are actually installing.
loading dimmers at less than 100 %
loading dimmers at less than 100 %
somebody, somewhere was once (correctly) told that when installing side by side dimmers in the same box they must be derated...this led to mistaken belief that no dimmer can be loaded at 100%...URBAN LEGEND STRIKES AGAIN!!!
loading dimmers at less than 100 %
somebody, somewhere was once (correctly) told that when installing side by side dimmers in the same box they must be derated...this led to mistaken belief that no dimmer can be loaded at 100%...URBAN LEGEND STRIKES AGAIN!!!
Not necessarily false. Some dimmers have fins on the front. If they are left intact, you can rate the dimmer to 100%. But in order to install them in a multi-gang box with similar dimmers, you must break some of the fins off. According to the instructions, you must then derate the dimmer.
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