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I bought a power strip like this one: https://www.elettronew.com/31192-large_default/universal-power-strip-for-5-sockets-with-switch.jpg and I noticed if I get very close there is a really low electrical sound, like a buzz; I tried with a different power strip, and I noticed the same sound.

It's really low, I never noticed it before and it's almost inaudible; I think, but I'm not sure, that it comes from the light, but I have no idea if it's normal, and what can cause it.

I read it could be small electrical arcs forming around the contacts and it's not normal, but I'm not sure if that's the case: it happens in different power strips, also if there is no load connected, and as I said I think it's located near the lamp.

What could it be, and it's normal?

Mauro
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    Does it feature a neon bulb indicator? If not, it should be dead silent. – winny Feb 26 '23 at 20:28
  • the contacts should not have any current flowing through them when there is nothing plugged into the power strip – jsotola Feb 26 '23 at 20:49
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    If there's a surge protector built in, a capacitor in the surge protector circuit might be vibrating due to piezoelectric constriction. If the power strip contains a common-mode filter, it could be vibrating due to electromagnetic forces (e.g. Lorentz force on a loose winding). It could maybe be a faulty GDT, but that seems unlikely. – Polynomial Feb 26 '23 at 21:47
  • It has a light indicator that flickers, not sure which technology it uses, and doesn't seem to have a surge protector (or, at least, it's not accessible from outside to be replaced); maybe I'll open it and check if I see anything. What's a GDT? – Mauro Feb 26 '23 at 21:52
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    The surge protector would be fully internal. A GDT is a gas discharge tube. Neon indicator bulbs do flicker, but then again LEDs tend to flicker too if they're driven from a rectified AC supply. – Polynomial Feb 26 '23 at 23:39
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    @Mauro does the indicator flicker when the room is dark, and glows solidly when bright light is shined on the indicator? – jsotola Feb 27 '23 at 02:10
  • @jsotola it flickers clearly also under direct light - I tried poiting directly at it my phone's light, and I can see it flickers, – Mauro Feb 27 '23 at 08:10
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    neon indicator lights will flicker in dark and light fully in bright light when they get old ... might still be a really old neon lamp – jsotola Feb 27 '23 at 09:10
  • @jsotola it has five to seven years. Meanwhile I tried to take it apart, but I'm unable to get a grip on the screws, not sure if they are glued or what else; I'll keep trying. – Mauro Feb 27 '23 at 09:54
  • what do the screw heads look like? ... they may be security slot screws – jsotola Feb 27 '23 at 17:19
  • They seem normal screws with + head to me: https://drive.google.com/file/d/1M2ZdyaF7R0zn2w_kRxkVB-3DsgeicAT0/ – Mauro Mar 01 '23 at 21:27

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A surge protector might draw significant current spikes at waveform peaks. You could try running the strip on a Variac and see if the noise is related to voltage.If you can, monitor the current on a scope to see if there are spikes. This might be normal, but repeated surges into an MOV will cause it to deteriorate and eventually draw high current and short out. There should be a fuse in series with it, and maybe an indicator showing it is working (conducting)

PStechPaul
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  • There is no indicator of any kind, I'll try to see if there is a surge protector inside. – Mauro Feb 27 '23 at 08:11