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Repeated dimmer failure

Posted by jon1270 (My Page) on
Fri, May 2, 08 at 17:20

When I remodeled my kitchen about a year and a half ago, I installed nine line-voltage 4" recessed lights which are controlled by two Leviton Illlumatech preset dimmers, with three cans/150W on one dimmer and six cans/300W on the other (these are 600W dimmers). Everything works fine, except that when a bulb burns out there's a good chance it takes the dimmer with it. A dimmer has failed three of the four times that a bulb has burned out since the initial installation. Only the slide dimmer fails -- the on/off button continues to work normally.

Leviton has been replacing the dimmers as I mail them in, but their tech support people are, so far, unable to imagine how a bulb's burning out could cause the dimmer to fail. They've speculated that it could be a problem with a fixture or a loose connection, neither of which ideas holds water; the failures have all been simultaneous with burn-outs in different fixtures, and there are no symptoms of loose connections anywhere.

I'm hoping someone here has a brilliant insight to offer. The bulbs, if it matters, are Sylvania 50W PAR20s.


Follow-Up Postings:

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RE: Repeated dimmer failure

You must be talking to low-level tech support. It's well known that an incandescent bulb can briefly draw a very large amount of current when it burns out, which can damage a dimmer that isn't tough enough to handle the overload. Google the term "burnout arc" for more information.


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RE: Repeated dimmer failure

friend...a couple of things comes to mind

A..perhaps we are running the dimmers at TOO high
an continous load . . .get some accurate meter
readings . .shouldnt be anywhere close to 80%
B...do the dimmers get hot ?

C...try revisiting all connections on that circuit
and check neutral connections in panel

D...electronic slider dimmers . . .if I know I need one
that needs to handle 600watts . .realistically
I'll put in a MUCH higher rated one . .

E..did you check the cubic inches required for the
number of conductors and devices in that box? . .
its a heat consideration..aand thus an lifespan
issue

F whats the life span on the bulbs them selves?

H...what else is on that circuit ..out of curiousity?

just thinking out loud here


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RE: Repeated dimmer failure

"Leviton has been replacing the dimmers as I mail them in, but their tech support people are, so far, unable to imagine how a bulb's burning out could cause the dimmer to fail."

That is amusing.

Bulbs can create a current spike at failure, and to prevent it from getting to large the wires feeding the filament are sized to limit the amount of current that can continue to flow.
Some are even deformed to create a 'hot spot' if excessive current flows and act as a fuse.
While the current pulse may be very short, the triacs used in dimmers are very sensitive to the slightest over current.

High temperatures increase the sensitivity to overload.
Unless there are other problems box fill factor should not be an issue.
Absent a bad connection, the wiring itself has a very small temperature rise.
Plastic boxes can increase the temperature (they do not conduct heat as well as metal) causing the dimmers to run hotter.

You could try higher capacity dimmers to get some extra margin on current, but even a 1000 W dimmer cannot deal with a brief high current surge very well.


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RE: Repeated dimmer failure

Sorry I let this drop off without acknowledging all the thoughts that were offered. I do appreciate the ideas, but I'm not seeing any one explanation that seems plausible:

Burnout arc sounds like an occasional freak occurance, but the problem I'm encountering is happening regularly -- dimmers have failed with three out of four burnouts, or 75% of the time.

These dimmers aren't loaded anywhere near their rated capacities. They are both 600W dimmers. One has not been derated at all and carries 300 watts, the other is derated because it's in a 2-gang box but only carries 150 watts.

The two dimmers are on completely separate circuits, in different rooms, with different breakers, powering different brands/models of recessed fixtures. The three burnouts that caused dimmer failure occurred in three different fixtures.

I have not checked every connection on every circuit -- there's no access from above, so checking every connection would necessitate pulling every fixture out of the ceiling, which I'm not eager to do, and which seems like a last-resort sort of idea since I'm not seeing the sort of symptoms I'd expect from a bad connection. Other than dimmers failing simultaneously with bulb burnout, there are absolutely NO other symptoms that anything is amiss. There is never any flicker, no buzzing, no unevenness in the brightness of the lights. Nothing.

I don't keep records of how often and for how long I use these lights, but the bulbs don't seem to be failing prematurely.

The breaker supplying the dimmer that carries 300W also supplies several outlets, while the one that supplies the dimmer carrying 150W of lighting also supplies several other light fixtures and a bathroom fan.

Anyhow, I do appreciate the thoughts but I'm still searching.


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RE: Repeated dimmer failure

The Triac is faily sensitive to current spikes that blowing bulbs can cause the Triac to fail. Triacs often fail closed so that it will not dim the lights any more. The manufacturer can better protect the triac from spikes, but they don't to cut costs. They work most of the time for a while until a blowing bulb takes it out. I am just attributing it to cheapness, and I have had good luck with the box stores and manufacturers giving me a replacement. Glad too see you to are getting refund/replacements.


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RE: Repeated dimmer failure

I think it is very plausible that the bulbs could do it. It might seem impossible to have this happen so many times and it be the bulbs fault. This wattage and series of bulb by Sylvania may be unintentionally by design more likely to high arc upon failure. I don't think you are getting enough longevity out of the bulbs if you have already lost that many in a year and a half. If the bulbs were purchased by the case it would be even more probable that something is wrong with that lot of bulbs.

Sylvania makes good bulbs but I am not so sure I wouldn't swap them with another brand or upgrade the dimmer if possible next time.


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