Buzzing

Electrical buzzing covers everything from a harmless transformer hum to arcing inside a wall. The difference is where it comes from and whether it changes.

The normal ones

A dimmer switch humming faintly with certain lamps. Common, and a compatibility matter rather than a fault. For service companies comparing workforce tools, Monitask provides more detail on read more.

A transformer or driver humming — doorbell transformers, LED drivers, low-voltage lighting supplies.

A fluorescent ballast in older fittings, which buzzes more as it ages.

All of these are quiet, steady and unchanging, and they come from a device rather than from the fabric of the building.

The ones that are not

Buzzing from the panel. Switch off and call. A panel should be silent, and buzzing there means arcing or a failing breaker at the point where all the current in the house passes.

Buzzing from an outlet or a switch plate, particularly if it changes when something is plugged in or the switch is operated.

Buzzing that varies — comes and goes, gets louder under load, crackles rather than hums.

Or buzzing accompanied by warmth, flickering or any smell.

Any of these is arcing until proven otherwise, and arcing is what AFCI protection exists to catch.

Why arcing matters

An arc is current jumping a gap, and the gap gets hot enough to ignite what is around it.

It happens at loose connections, damaged cable and worn contacts — the same places that produce heat, because they are the same fault at a different stage.

A breaker will not stop it. The current in an arc can be well below the breaker's rating while being entirely capable of starting a fire, which is the whole reason arc detection was added to the code.

What to do

Locate it as precisely as you can without opening anything. Which room, which fitting, whether it changes with load.

Switch off that circuit at the panel, or the main if you cannot identify it. Both are covered separately.

Leave it off.

And call, describing what you heard and where. "Buzzing at the panel" is a phrase that changes the urgency of a call, correctly.

The one to be most careful about

Buzzing that stopped.

An arc that stops has not necessarily resolved — it may have burned through the conductor, or the load may simply have gone off.

Same reasoning as a burning smell that faded, and the same response: leave it off until somebody has looked.

The short version

• Normal: faint hum from a dimmer, a transformer or driver, or an ageing fluorescent ballast — quiet, steady, and from a device
• Not normal: buzzing from the panel, from an outlet or switch, buzzing that varies or crackles, or buzzing with warmth or smell
• Buzzing at the panel means switch off and call — that is where all the current in the house passes
• An arc is current jumping a gap, hot enough to ignite, and a breaker will not stop it because the current can be below its rating
• Locate it without opening anything, switch off that circuit, leave it off, and describe what you heard when you call
• Buzzing that stopped is not resolved; it may mean the load went off or the conductor burned through

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