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I am having a discussion with coworkers about sufficient grounding to a chassis... my opinion is that a toothed ring terminal in contact with bare metal is required, e.g. Molex 19074-0025, so that the teeth will scrape through any oxidation layer:

enter image description here

(Alternatively a regular ring terminal with a toothed lock washer.)

Someone else suggested a Faston tab like the ones in the picture below:

https://www.flickr.com/photos/mouser-nerdbot/4676010617

I am uncomfortable advising use of these terminals, or any other connectorization of earth grounding.

Any suggestions?

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  • \$\begingroup\$ Soldered, they're ok. Still not as rugged as a toothed-ring terminal. All said and done, toothed-ring is less work. \$\endgroup\$
    – rdtsc
    Feb 4, 2016 at 15:51
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    \$\begingroup\$ The Faston tabs can't become accidentally loose or providing intermittent contact? (re: soldering -- I have heard anecdotally that crimping is more robust than soldering to stranded wire, since crimping provides a measure of strain relief, whereas soldering provides points of strain concentration at the edge of the solder joint.) \$\endgroup\$
    – Jason S
    Feb 4, 2016 at 15:54
  • \$\begingroup\$ see also this comment about soldering vs. crimping for earth grounding: music-electronics-forum.com/t16327/#post132718 \$\endgroup\$
    – Jason S
    Feb 4, 2016 at 16:04
  • \$\begingroup\$ In addition to the other comments, I generally use an internal-tooth lock washer between the chassis and the fast-on terminal. \$\endgroup\$
    – Dwayne Reid
    Feb 4, 2016 at 16:11
  • \$\begingroup\$ Of course Fast-Ons could come loose. Soldering prevents this, and the wire retains the crimped connection only. Not so easy to remove afterwards though. It's my preference to tack Fast-ons if they must be used, but I don't like them. The UL code may require toothed-ring, I am not sure; but they certainly prefer them over any sort of Fast-on debauchery. \$\endgroup\$
    – rdtsc
    Feb 4, 2016 at 16:12

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In the 2000s, we have designed and put through UL a medical device that's mains-powered and has electrodes on the patient. One of the comments from UL was to do the earth connection with ring terminal and star washer. They have also required that the screw for the terminal can not be unscrewed from the outside. Initially, we had the earth ring terminal screwed to the case with a machine screw and a nut. We replaced the screw with a press-in threaded stud.

Later, I was salvaging a different medical device (3rd party device, I wasn't involved in the design, or knew designers). I would guess that it was from the early 1990s. Some of the outside panels were grounded through wires with Faston terminals.

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  • \$\begingroup\$ "They have also required that the crew for the terminal can not be unscrewed from the outside. We replaced a screw with a press-in threaded stud." -- really? I wonder why that is. \$\endgroup\$
    – Jason S
    Feb 4, 2016 at 21:04
  • \$\begingroup\$ A technician can accidentally loosen the wrong screw and break the earth connection without even knowing. (At the same time, I don't know if "shall not be unscrewed from outside" is mandatory for consumer devices.) \$\endgroup\$
    – Nick Alexeev
    Feb 4, 2016 at 21:09
  • \$\begingroup\$ Huh. I wonder if that is ok if you use a grounding screw \$\endgroup\$
    – Jason S
    Feb 5, 2016 at 2:04
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    \$\begingroup\$ It's a thread-forming (self-tapping) screw, and it works without a separate nut. If the screw head is on the inside, it should be okay. (If you had a regular machine screw with a separate nut, and the screw head or the nut is exposed to the outside, then the ground connection can be loosened from the outside.) \$\endgroup\$
    – Nick Alexeev
    Feb 5, 2016 at 2:14

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