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I'm running some 6 ga armored bare copper wire through the attic spaces as a "grounding bus" for retrofitting grounds to various 1960s-era 2-prong receptacles. This will involve wire connections made with the 6 ga in a number of 4x4 steel junction boxes along the way in the attic, but I also want to properly bond the 6 ga to each metal junction box.

To do that, I plan to secure the 6 ga incoming wire end to a tinned lug as seen in the photo, and secure the lug to the junction box with a standard green 10-32 grounding screw and the box's pre-threaded hole for the same. The mounting hole in the lug is however 1/4 inch, so bonding connection will rely on the contact of the lug surfaces with box underneath and screw clamping from above. Is this sufficient? Kopr-shield will be used on the lug set screw and wire, and on the underneath of the lug where it contacts the box.

EDIT: @HABO The plan is to connect the end of the incoming ground wire to a lug attached to the box. Slightly upstream of that connection in the box, a split bolt would be used to connect the outgoing ground wire to the incoming wire. Any 10/12 ga EGC wire coming into the box would also be connected to the incoming ground wire via split bolt. I expect that a number of the boxes will have no EGC coming in at this point, being present for possible future use with other 2-prong outlet upgrades.

@blarg I did not find manufacturer (Southwire) provided instructions for lug mounting, but I have not made an exhaustive search. I have #6 bare armored ground wire and clamps/fittings on hand (100') and may need to add stove and/or dryer EGCs in the future, so this seemed straightforward to use.

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Armand
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  • Are there manufacturer provided instructions? The code requirement is to follow those. Is there a reason you are going with #6? – blarg Mar 25 '23 at 09:54
  • Will the armored bare cable terminate at each box or continue ("along the way") to subsequent boxes? If it will continue then you need to determine how you will connect the incoming, outgoing and pigtail wires in each (non-terminal) box. That also requires more space, in the NEC sense, since a connection is "larger" than a wire just passing through. The pigtail doesn't need to be 6ga. – HABO Mar 25 '23 at 13:47
  • @HABO Updated question with further explanation – Armand Mar 25 '23 at 19:07

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Use a lug that's intended to accept the correct size screw

Instead of trying to hack things with a lug whose mounting hole is too big, I'd simply use a lug that has the correct size mounting hole in it. The IHI S6-203 provides sufficient wire range for your application in the same style as the lugs you're already looking at, while the Burndy CL501TN is a copper-only lug but in a lay-in style that can speed installation. If you want a dual-rated lay-in lug, your best option is the Ilsco GBL-4 but its hole is slightly fatter than necessary (more sized for a #12 than a #10 although Ilsco specifies it ofr the latter).

ThreePhaseEel
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  • Thanks! I have found a cheap source of the Ilsco GBL-4DBT version, so I will use those for this. I assume the lugs with 1/4 inch hole can be used in the future with a 1/4 bolt, lock washer and nut, so I'll hold on to them for now. – Armand Mar 25 '23 at 19:19
  • @Armand yeah, one could do that provided the paint's scraped clean, I reckon – ThreePhaseEel Mar 25 '23 at 20:58
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    @Armand also, with the layin lugs, you can eliminate a lot of hassle by using a Garvin/Southwire GSST to screw them to the *outside* of the metal box then looping the wire through them. of course, you can do things with a split bolt or T-tap connector and drop wire for boxes in walls and stuff, too – ThreePhaseEel Mar 25 '23 at 20:59