I'm starting to design things that run off mains voltage and I want to be sure that I have a proper connection from my chassis to earth ground.

I've been reading a bit about proper grounding and have learned the basics about stripping any paint off the chassis near the grounded point and connecting earth to the chassis as shown in this picture:

Proper grounding

Image source

Finding the right hardware is easy enough, I plan on using all #10-32 machine screws and the associated nuts/washers.

I'm curious how other people on this site choose an "approved earth lug". I was thinking of using one of these.

I'm not exactly sure which agency's approval I am looking for. I'm also generally curious what other people have used in their designs. If some of you could share some part numbers for lugs you like to use, that would be helpful.

Additionally, I learned here that NEC requires the earth wire to be at least 14 AWG, while IEC requires 18AWG. I'm not exactly sure what situations call for meeting either of these specs.

So to summarize:

  1. Can someone give a few examples of ground lugs they like to use in their designs? Extra points if it doesn't require an expensive crimp tool.
  2. When is it important to use 14AWG rather than 18AWG for the earth wire?

[Edit: I should add a few notes that relate to agency approval. I live in the US and I'm designing devices for personal use, nothing to sell. None of my devices necessarily need to be approved by any agency, safety is my only real concern.]

  • 1
    \$\begingroup\$ In the USA, UL requires that the Earth ground wire be the same gauge as the hot and neutral wire. This is not a problem if it is a 3-wire cable, as all wires are normally the same gauge. \$\endgroup\$
    – user105652
    Feb 15, 2019 at 22:04
  • \$\begingroup\$ @Sparky256 that makes sense. So I guess that's where the 14AWG number comes from since that's the minimum gauge for house wiring as well? I plan on using an IEC C14 connector so I guess I would have to just match the gauge of the cable connected to it? \$\endgroup\$ Feb 15, 2019 at 22:09
  • 1
    \$\begingroup\$ That would be correct. \$\endgroup\$
    – user105652
    Feb 15, 2019 at 22:27

1 Answer 1


In the USA these are the issues to deal with for grounding a metal enclosure to UL standards. They are common sense reasons whether you build one for yourself or build a 1,000 per year.

As I mentioned as a comment UL requires that the Earth ground wire be the same gauge as the hot and neutral wire. This is not a problem if it is a 3-wire cable, as all wires are normally the same gauge. If using wire nuts to convert from solid to stranded wire the stranded wire needs to be the same gauge as the solid wire.

As for the chassis ground we used 1/4-20 SS bolts about 3/8" to 1/2" long. A crimp-on lug is the best way to go. Use a hammer if you do not have the proper crimper. You MUST use a grounding type washer, which has teeth both inside and outside, and it goes on the bolt before the lug does to create a very low resistance connection to the chassis. The nut goes on last.

You are not selling it so no need for labels, though at some hardware stores you may find a generic "High Voltage" label you can put on the door or cover. It may remind you to shut off the breaker or disconnect switch before working on it in the future.

  • \$\begingroup\$ For the grounding type washer, would something like this work? \$\endgroup\$ Feb 15, 2019 at 23:33
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    \$\begingroup\$ Any washer would do since UL is not going to inspect your device. Technically from UL's point of view a proper grounding washer has both inside and outside teeth. You are not obligated to follow exact UL standards. It is your choice. \$\endgroup\$
    – user105652
    Feb 15, 2019 at 23:50

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