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A desk computer is making odd buzzing sound exactly when welding machine in other room is being used. Is it because they share same electrical grid?

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  • \$\begingroup\$ What kind of welding machine? How is it supplied? 230VAC? 3 phase 400V? \$\endgroup\$
    – Lundin
    Mar 18 at 10:50

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Likely this is "coil whine" caused by electromagnetic interference (EMI), which could for example happen inside the PSU or maybe the motherboard or graphics card. Very annoying but probably harmless. It could be caused by conducted electrical emissions - wire-bound over the power grid, but it could also be caused by radiated emissions through the air.

Many bad, non-conforming PSUs didn't consider that a PC is a multimedia device where one of the purposes of the product is to play sound. Properly designed PSUs will test for electromagnetic compatibility (EMC) against a broad range of electrical noise frequencies, to ensure that they get no coil whine at certain frequencies. I had a bad one myself which would start to whine as soon as the graphics card did something fancy.

So the most likely reason is that your PSU wasn't properly designed. There should be a decent EMI filter integrated directly on the PSU input from 230VAC. At the very least ensure that the PSU is marked with an UL mark one of these (the CE mark doesn't mean jack). But not even this necessarily means that the PSU is compliant, only that the manufacturer managed to find a fishy-enough test house.

It could less likely be something else inside the PC or the welding equipment causing it. I would btw recommend to put welding equipment on a mains connector with a dedicated fuse of it's own.

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  • \$\begingroup\$ "your PSU wasn't properly designed" I don't fully agree. Products are generally EMC compliant for a specific environment. Products like a welder for industrial environments can have (but must also withstand) much higher emissions than products made to be used in an office. So when a welder and a PC are placed together in the same environment, they are simply not guaranteed to be electromagnetically compatible to each other. \$\endgroup\$
    – Klas-Kenny
    Mar 18 at 12:39
  • \$\begingroup\$ @Klas-Kenny I think the welder is probably irrelevant, there are a whole lot of things in a home environment that could cause similar conducted and/or radiated emissions. Ovens, water boilers, electrical lawn movers with wire, a starter engine in the garage next door, a moped passing by on the street outside. And so on. \$\endgroup\$
    – Lundin
    Mar 18 at 12:54
  • \$\begingroup\$ Well, not really. Since the oven, boiler etc. will need to comply with EMC requirements for residential use. The radiated emissions from a moped on the street will be nothing compared to conducted emissions from the welder. Surely when two (from the EMC requirements point of view) different environments are very close together like this there is a gray area that might induce problems, which is likely exactly what OP is experiencing. \$\endgroup\$
    – Klas-Kenny
    Mar 18 at 13:10
  • \$\begingroup\$ @Klas-Kenny Btw there's not a lot of differences in EMC compliance for industrial and commercial use. I'm not super up-to-date, but I believe for example radiated susceptibility tests are around 30V/m in either case. Some industrial sub-standards name tougher requirements, like various standards for earth-moving machinery requiring 100V/m etc but these are essentially automotive applications. \$\endgroup\$
    – Lundin
    Mar 18 at 13:52
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A similar issue happens when I use my radio equipment in my room. A loud buzz comes through the speakers.

It's interference getting picked up by the wire going to the speaker. A shielded wire can fix this - Try wrapping your wire in aluminum foil connected to ground.

When your welder is running, the high voltage can create an electric field that causes electromagnetic interference.

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