A buzzing sound coming from a recessed lighting fixture may be a harmless annoyance, or it might warn of a much more dangerous problem. With fluorescent fixtures, the buzzing sound is usually benign. With recessed incandescent, high intensity discharge and light-emitting diode fixtures, however, the buzzing sound can indicate potential fire hazards, such as loose electrical connections and defective light sockets. Before making repairs on any light fixture, turn off the branch circuit breaker supplying the light fixture at the service panel.
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With fluorescent light fixtures, the most common causes of buzzing are defective ballasts. The older style ballasts are nothing more than auto-transformers with laminated iron cores. As these transformers age, the thin lamination making up the laminated transformer core have a tendency to come loose inside the coil windings. The electromagnetic lines of force coming from the coils pass through the loose laminations, causing them to vibrate, which generates a buzzing sound. To correct this problem, replace the old ballast with a new one. Remove the light bulbs and the ballast cover. Disconnect the wires from the old ballast, remove the two nuts holding the ballast to the fixture and remove it from the fixture. Replace it with the new ballast.
A buzzing sound coming from an incandescent light fixture is most often caused by a defective light socket or a loose bulb. The buzzing sound is actually a manifestation of electrical arcing between the center contact on the base of the bulb and the button contact at the bottom of the light socket. In many cases, the button contact loses tension with age and no longer presses tightly against the bulb's center contact. Besides age, over-lamping -- putting a 100 watt bulb in a 60 watt outlet, for example -- can damage the socket contacts, leading to arcing and the buzzing sound. Replace the lamp sockets to fix this problem.
High Intensity Discharge Lights
High intensity discharge lighting uses a transformer similar to the ballast used in fluorescent that is prone to buzzing because of loose laminations. These lights also use a capacitor that is subject to both internal and external arcing. External arcing can usually be detected by the carbon path buildup between the terminals. Internal arcing isn't easy to detect, so if you suspect this, simply replace the capacitor. Capacitors can store an electrical charge for days, so discharge it by shorting its terminals out with the blade and shaft of a screwdriver with a solid plastic handle before touching the capacitor's terminals. Touch the tip of the screwdriver to one of the terminals while pressing the shaft of the screwdriver against the other terminal.
Loose Electrical Connections
A less common cause of buzzing coming from any light fixture is a loose electrical connection. Most electrical splices are made today using screw-on wire nuts, a type of solderless connector. A wire nut can work loose, allowing arcing between the wires it was holding together. The arcing is detected as a buzzing sound and, in the case of incandescent lights, a flickering of the light itself. The buzzing in this case tips you off to a potential fire hazard. If not corrected, the arcing generates heat that can ignite surrounding structural materials.