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I am working on a project that uses 120VAC power. I have made a lot of enclosures for low voltage projects in the past, but this is my first high voltage project that needs an enclosure.

I am wondering what my options are, and what precautions I need to take to ensure my project is safe.

Ideally I would like to use a powder coated aluminum enclosure, as it matches the aesthetics of my past projects and also because I have a supplier that can do machining / uv printing at an affordable rate (enclosure prices elsewhere have generally been exorbitant, or require that I do all the machining / graphical work by hand). I want to check that this is safe and ask what precautions I should take before designing my project around this process.

Is aluminum safe? If so, should I ground the chassis? Are there other precautions that I need to be aware of?

The power input of my project is a 10A rated IEC socket, but I will likely fuse the project at 5A, in case that information is relevant.

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    \$\begingroup\$ Is this a personal project, or will you be selling it? In the first case, "safe enough" is whatever you feel comfortable with. In the latter case, "safe enough" is a matter of legal opinion -- you could still sell bare wires on a wooden board, but you probably want to either actually get UL ratings for the things, or at least design them as if you were going to. "Will it burn my house down" and "can I or my children get electrocuted" are probably the two main questions that you want to answer "no" to. \$\endgroup\$
    – TimWescott
    Sep 18 at 20:53
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    \$\begingroup\$ Ground the chassis. \$\endgroup\$ Sep 18 at 20:54
  • \$\begingroup\$ @TimWescott This is mostly a personal project that I may be making a small run of to share with friends and other interested parties, so somewhere in between, but more on the casual side of things. Safe in this case means that a person can use it while being reasonably safe from electrocution. \$\endgroup\$ Sep 18 at 21:31
  • \$\begingroup\$ Is mains power used throughout the board? If not, you can just use an onboard isolated AC-DC supply, then you only have to worry about the high voltage pins on the AC-DC supply. \$\endgroup\$
    – DKNguyen
    Sep 18 at 21:54
  • \$\begingroup\$ @DKNguyen The project is an audio controlled AC dimmer. So there is an ac triac dimming circuit with ac input and output, as well as a low voltage section powered by a small ac to dc converter module \$\endgroup\$ Sep 18 at 21:56
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For personal mains-powered projects, I let the metal-cased stuff around my house be a guide: make sure that anything that carries 120V can't be touched by a finger from the outside of the case, make sure the case is non-trivial to open (basically -- use screws, not latches), make sure that the construction is solid enough so that if the thing is dropped the safety is still there (i.e., nothing breaks off inside and the case doesn't spring open), make sure it's fused (so, no lighting the house on fire), and make sure that 120V doesn't appear on the outside of the case unless at least two things go wrong.

That "unless two things go wrong" part can be handled by using a 3-wire plug and grounding the case, which is usually the easiest way to go.

If you're going to sell it as a commercial venture, then for your own protection you'll want to get it UL approved. Or, just shop it around to two or three Chinese contract manufacturers, and wait for a clone product to appear on store shelves here.

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  • \$\begingroup\$ Got it, thanks for the very clear and detailed answer. \$\endgroup\$ Sep 18 at 21:58
  • \$\begingroup\$ What's up with the contract manufacturers? Sounds like there's an interesting story there 🤔 \$\endgroup\$ Sep 18 at 21:59
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    \$\begingroup\$ Basically, “mister manufacturer, we’d like you to make this headphone radio set. Here’s a prototype.” Two months later you see a practically identical item at a sketchy flea market in a box labeled “cranial audio reception.” \$\endgroup\$ Sep 18 at 23:17

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