WiremanWireman · Dimmer buzzes, gets hot or won’t dim: troubleshooting for electricians · 2023 NEC ·
Dimmer buzzes, gets hot or won’t dim
Buzzing, heat, flicker at low settings and LEDs that won’t dim smoothly.
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How it works
Most wall dimmers are phase-cut: they switch the AC off for part of each half cycle, so the lamp gets less average power. That fast switching makes some heat in the dimmer and can make lamp filaments and cheap drivers buzz. Leading-edge (forward-phase, often called TRIAC) and trailing-edge (reverse-phase, often called ELV) dimmers cut the wave differently, and LED drivers each like one or the other. A dimmer’s rating drops when it’s ganged with others and its side fins are removed, and its LED rating is usually far lower than its incandescent rating.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What’s the problem?
- Buzzes or humsWhere is the buzz coming from?
- The dimmer in the wallTest: Compare the load to the dimmer ratingExpect: Total load at or below the dimmer’s rating for that lamp type and gang arrangement.
- Over the ratingToo much load on the dimmer
- Within the rating, but the dimmer is hotA loose connection or failing dimmer
- Within the rating, only warmNormal dimmer warmth
- Incandescent or halogen bulbsFilament buzz from phase-cut dimming
- LED bulbsAre the lamps marked dimmable, and is the dimmer rated for LED?
- No, or not sureLamp and dimmer not compatible
- Yes to bothDoes the dimmer have a low-end trim adjustment, and has it been set?
- Not set, or no trimLow-end trim not set
- Set, still flickersWrong dimming type or too little load
- The dimmer in the wallTest: Compare the load to the dimmer ratingExpect: Total load at or below the dimmer’s rating for that lamp type and gang arrangement.
- Hot to the touch, not just warmTest: Compare the load to the dimmer ratingExpect: Total load at or below the dimmer’s rating for that lamp type and gang arrangement.
- Over the ratingToo much load on the dimmer
- Within the rating, but the dimmer is hotA loose connection or failing dimmer
- Within the rating, only warmNormal dimmer warmth
- LEDs flicker, drop out or won’t dim lowAre the lamps marked dimmable, and is the dimmer rated for LED?
- No, or not sureLamp and dimmer not compatible
- Yes to bothDoes the dimmer have a low-end trim adjustment, and has it been set?
- Not set, or no trimLow-end trim not set
- Set, still flickersWrong dimming type or too little load
- It controls a fan or motorA light dimmer on a motor
- Light won’t turn fully offLeakage current through the lamp
- Buzzes or humsWhere is the buzz coming from?