About those power boxes that are in cities: https://i.stack.imgur.com/5SoTx.jpg

I can hear from a couple of on ground power boxes a very noticeable buzz of electricity.

There are a few power line poles with much larger transformers than the ones in the picture and other parts that I don't recognize that also emit a moderate amount of noise.

Is there any concern of radiation when walking near them?

Isn't the noise an indication of high voltage that's being discharged? That's basically how an x-ray machine works no?

If it matters, I live in a country with 220V outlets.

  • 2
    \$\begingroup\$ You should immediately move to a location far away from any power source; I would recommend 1km for every volt in a power source, so not within 220km of any power outlet, etc. so if there is any 360kV line around you should move really far away... \$\endgroup\$
    – PlasmaHH
    Sep 23, 2015 at 13:35
  • \$\begingroup\$ Yeah, I figured this would sound like a joke to professionals but it's a serious question. @PlasmaHH \$\endgroup\$
    – shinzou
    Sep 23, 2015 at 13:37
  • \$\begingroup\$ @Funkyguy: Ionizing radiation is not equal to nuclear radiation. X-ray and extreme UV is also ionizing. \$\endgroup\$
    – sweber
    Sep 23, 2015 at 13:38
  • \$\begingroup\$ I know that, that's not what I asked about, x-ray is generated with high voltage. @funkyguy \$\endgroup\$
    – shinzou
    Sep 23, 2015 at 13:39
  • 1
    \$\begingroup\$ I actually initially upvoted the question because, while really basic and ignorant, it wasn't necessarily stupid within your level of knowledge. However, I changed that to a downvote when I saw you were being a dick about others adding the image. The image helps a lot to clarify what you think a "power box" is. \$\endgroup\$ Sep 23, 2015 at 15:01

3 Answers 3


First of all, no, those devices do not generate ionizing radiation. The humming noise of 100 or 120Hz are vibrations of the transformers. This is due to magnetostriction, i.e. the transformer contracts when the magnetic field increases and expands, when it decreases. This happens twice per period, so you will hear 100Hz for a 50Hz AC net.

However, if you're looking for ionization effects in power transmission lines, you have to look at really high voltages. Then, the strength of the electric field can be high enough to ionize the air locally, which is called corona discharge. Here is a picture from a 500kV overhead line:

enter image description here

The violet color is typical for ionized air. Though you usually don't see this, you can hear a crinkly noise under a very high voltage transmission line, especially in wet weather conditions.

But it has to be said, this still is no ionizing radiation, though air is ionized.

  • \$\begingroup\$ You did mention it at the bottom, but it's worth emphasizing more, a corona discharge can ionize the air but it is NOT ionizing radiation. Given the asker's misunderstandings, that is important to note I think. \$\endgroup\$ Sep 24, 2015 at 12:17

No, they can't.

  1. The discharge over the isolators is minimal

  2. The median free run length of electrons in air is rather short (520 nm). So they cannot gather enough energy to emit ionizing radiation.

  3. The devices themselves do not provide any discharges, only moderate currents.


The sound is due to magnetostriction, the switching of the currents direction back and forth causes the ferrous material to expand and contract at the line frequency due to the magnetic domains switching. In terms of ionizing radiation, that occurs only in extremely high frequency electromagnetic waves. The number of volts don't necessarily mean ionizing or not. In physics, energy is related to wavelength and frequency, and the higher the frequency the higher the waves energy content. The electromagnetic waves medium is the field of electron charge, essentially it's a wave propagating through this field. If the energy is sufficient it can strip away electrons, thus is ionizing. The energy content from a basic line transformer is no where near high enough to be ionizing.


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