This transformer is installed in the utility closet of a 1970's condo.

photo of transformer mounted on wall

Notice the wad of cut paper sheets pinched between transformer and the wall plate. This is an attempt at halting a low-tone humming caused by the transformer. Is there a better way to avoid this annoying hum?

And should a transformer be exposed in the open like this? If this is proper, are there covers available to hide the ugly and protect the wires?

  • It is literally the job of a utility closet to contain 'ugly' utilities. While I'm all for a neat panel, utility space is supposed to look industrial. Commented Sep 30, 2020 at 4:05
  • Asking more than one question in one post is frowned upon. That said, to answer the secondary question that shouldn't have been included: it's very common to see a doorbell transformer mounted like that. The transformer probably has a threaded conduit stub with a nut that holds it to the metal plate, with the line voltage wires hidden behind that plate. This isolates line voltage from low voltage (a code requirement). The low voltage is permitted to be exposed since it's basically harmless. If you cover it, make sure the cover has venting to let the heat out. Commented Sep 30, 2020 at 7:28

2 Answers 2


The best way to eliminate transformer noise is to purchase a quality transformer. The noise is because the laminated core is heavily loaded or overloaded and the plates are actually vibrating because of eddy currents. I can’t quite make out the size, but it looks like 24V, 20VA. I would bump it up to a 24V, 40VA unit that would be compatible with video doorbells and probably a lot quieter. Usually, hard mounting is fine unless the core is coming apart or overloaded so going to a new larger one fixes both problems.


First, even though the exposed wires are low-voltage, likely 16 VAC, they should be covered for esthetics (if the transformer were accessible to children, not inside a closet, it is likely required). That said, the buzzing noise is likely being transmitted to the metal plate and wall, which make it much louder. A few things to reduce the buzz:

  • Remove the transformer from the metal plate and reinstall it using rubber grommets in the mounting holes of the transformer and of the cover plate, but run a ground wire from the box to a mounting lug of the transformer. This would also reduce vibration of the plate cause by the transformers magnetic field, effectively making the plate act as a loudspeaker.
  • Put sound-deadening tape inside the metal box cover. Perhaps a local garage has a small left=over piece? Golf-club weighting tape might also work.
  • Install a replacement of the correct voltage and current or VA rating, in the hope it would be quieter. A similar transformer might be ~US$10.

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