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I have a metal light switch box that is mounted on the outside of a wall and I would like to set a magnetic flashlight on it. Is electricity adversely affected by having a magnet near it?

  • Do you rune PowerLine ethernet anywhere? – MooseBoys Sep 22 '17 at 1:43
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Short answer: No.

Long answer: Nnnooooooo.

Serious answer: A permanent magnet, even one a thousand times stronger than the one holding your flashlight in place, placed near your home wiring but not moving has no effect on the circuit at all. A permanent magnet as small as the one on your flashlight, when moved around near your home wiring (eg. when you take the flashlight and put it back), will theoretically generate tiny surges of current in the wires. In order to measure those surges you would have to be a very careful physicist.

A magnet moved around near a metal junction box will generate tiny surges of current in the box walls. In order to measure those surges you would have to be a very careful physicist with pernicious insomnia. Theoretically a tiny amount of magnetic influence makes its way into the interior of the junction box, via screw holes etc. In order to measure those surges you would have to be a very careful physicist who is going through a bad divorce and expects to never sleep again.

All this is of no practical consequence. Any magnet you would have around the house cannot interfere with your domestic electric supply.

  • If that's your serious answer, I'd hate to see a flippant one! – Mark Ransom Sep 21 '17 at 21:07
  • I like the Llloooooong answer too! – Jimmy Fix-it Sep 22 '17 at 1:38
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    This won't affect GFCI and the likes? I can imagine them going partially blind, similarly to what happens if a DC current is present. – Mast Sep 22 '17 at 13:29
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    @Mast: Interesting. - The metal junction box should defend the GFCI from any nearby moving magnet. - But that would be an interesting experiment -- trying to trip a GFCI, that is not in a metal box, by waving a strongish magnet at it. – A. I. Breveleri Sep 22 '17 at 13:50
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Won't make a difference

For one thing, the steel box is going to weaken the magnetism.

But even if the magnet were in direct contact, it still wouldn't have an effect. Because you don't have anything like a transformer or motor winding there.

(To answer the inevitable question, magnets can reduce the effectiveness of a transformer core. Imagine you're jogging around your oval 1/4 mile high school track, round and round. Then the glee club sets up a stage, intruding on one end and forcing you to shortcut, that's like static magnetism intruding upon and saturating a transformer core. Now it's not 1/4 mile anymore. Thieves stick magnets on old style electric meters hoping it would under-report how much power they used.)

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Going to tack-on an answer.

Even though your specific question has been answered 100% correctly, I want to point out that you should never stick anything magnetic to a computer or other delicate electronics.

When putting the light on the junction/switch box the amount of EMI generated is so tiny it really can't hurt anything.

When putting that magnet on a computer or similar, it could really mess things up.

First it could effect magnetic storage (tapes, and hard drives for example), and in some cases it could alter the "signal" voltage in, for example, Ethernet cables enough to cause issues. Mostly though, the magnet, could, if strong enough, alter the voltages enough on the circuit lines of delicate electronics enough to cause issue.

The most common effect is likely to be distortion of other magnetic fields though, and not that of actual voltage.

That said, it's perfectly fine to stick where your describing, I just wanted to pop in and make sure it's clear that it's not ok to sick on, say, the back of a plasma TV, or your favorite collection of floppy disks.

  • As evidence of this, my son, when younger, discovered that holding a magnet up to the TV made the picture look "cool". He got bored but left the magnet there for a while. After discovery of the magnet and a stern lecture about it, it took about a week for the TV to not look so "cool" any more. (When said child was younger, the world only knew of CRTs, not LCD TVs...) – FreeMan Sep 22 '17 at 13:42
  • That's because the magnet adds a bit of magnetism to the colour (or color) mask in the CRT display and the added magnetism bends the electron beams. Some monitros used to have a degauss button that could be used to blip the stray magnetism off the mask... most useful when a company I worked for gave everyone a publicity -printed magnetic pyramid covered in paper clips and many users put them on top of their screens. – matt Sep 22 '17 at 14:24
  • You can remove the part about it impacting PCs. There is no component in a PC that will be impacted in any amount by a magnet the average person has access to. – Bryan Boettcher Sep 22 '17 at 15:14
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In general no, it will be fine.

I would however avoid putting strong magnets near electricity meters. The accuracy on some models can be affected by the magnetic field, and others have sensors that will indicate a "tampering event" to the electricity company if they detect a strong field.

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