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grounding of metal box power electronics

Safety when creating electronics enclosure

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I’m designing an electronics enclosure to be placed in series with the power cord for a device for control purposes and would like to know safest methods to do power breakouts within the plastic box. I’m planning on putting a power entry module on one end or possibly two to make the power breakout easier. I’ve seen terminal blocks but mostly used for DIN rails/control panels, not small enclosures. I only need 2 separate sets of hot/neutral/earth, one of which will be fed to a 5v power supply. I’d also like to know how to test wiring in something like this since I want to be sure the 120v lines are very secure and there’s no potential for loose connections/soldering. There will be a relay switching 120v that goes out through another plug also, so don’t know if that changes any protocol. Thankspower5venclosureshareedit  follow  flagedited 10 hours agoasked 11 hours agocoolro3944 bronze badges

  • 2UL has a specification for strain reliefs, I think something like 35lbf (~155N) minimum pull-out strength. – Spehro Pefhany 11 hours ago
  • 1Is this a hobby thing or are you designing a product that’s gonna be marketed??? – Kyle B 10 hours ago
  • 2Power cables with molded plugs on one side often have a molded flange on the other side which sits in a slot in the plastic box. For hobby use, I make liberal use of cable ties (including to hold the PCB). For making to sell, I guess, one might have to find a custom box manufacturer. – Indraneel 10 hours ago 
  • 1@KyleB this is for hobby only – coolro 10 hours ago 
  • 1@coolro For hobby, make a smallish hole in the box, put the mains cable in, then put a cable tie on it to stop it from slipping out. It will be as good as any cheap chinese stuff. Otherwise, you can design a strain relief on a piece of plastic or plywood and cable tie the plastic/plywood to the inside of the box. – Indraneel 10 hours ago 
  • 1ADD A FUSE!!!!! Nobody does everything right 😉 Fuse goes on the ‘hot’ wire (or ideally both). The wire should come into the box, hit the fuse, THEN move on to switches or whatever. Keep the high-voltage wires separated by at least 1/2″, and tie them down somehow so they can’t wiggle free. For my hobby stuff, my ‘strain relief’ is often just a few layers of shrink wrap. Something to keep the wire from bending at 90 degree angle. – Kyle B 10 hours ago
  • A year ago, I started making a metal box to put my power electronics stuff in. I showed off my master piece in another Rpi forum, hoping to let my bad friends got jealous and started to respect me more than I deserved. But I had an unpleasant surprise: I got many warnings from EE experts, including registered electricians. I have some links with pictures, in case you are curious what kind of warnings I got. Here are the first couple of pictures: DIY a 220VAC to 24VAC 5V Realy Control Box (1) raspberrypi.org/forums/… / to continue, … – tlfong01 10 hours ago    
  • (2) raspberrypi.org/forums/… (3) raspberrypi.org/forums/… (4) raspberrypi.org/forums/… (5) penzu.com/p/e7572bdd. Ah bed time. See you over the locking down weekend. Cheers. – tlfong01 10 hours ago    
  • 1Another couple things not listed: get a high quality PCB. If you can find UL94 V-0 compliant boards, get those. They will be more expensive, but when something goes wrong at least you know your board is not going to burst into flames. To be extra safe, all stranded wire should be either crimped into a connector, lug, or ferrule for the most reliable connection. Add MOVs across the line and from each line to PE, this will protect your circuit from surges and such on the line. – Stiddily 9 hours ago
  • 1What are best techniques to soldering onto the terminals of power entry modules? Is there a specific thickness of solder required for that? I also saw some people using butt crimps but didn’t think that was used for metal terminals, only two wires together – coolro 8 hours ago

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