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I was introduced to grounding bushings in this answer to a previous question of mine, but couldn't actually find them anywhere for weeks. Finally I bought this one off Amazon, and it arrived this week!

enter image description here

When I tried to use it in a Tesla charger today, I realized how huge this was. It was too big to rotate inside the plastic box, and even if I rotated the EMT's terminal fitting from outside instead, I found it's still too big for the box to close on it.

Maybe(?) I could have fit it inside an extra-deep square metal box, but at that point why would I even need this? It's only useful for plastic boxes, but it seemed too big to be practical there.

Also, size aside, the product packaging only talks about use with Rigid or IMC (but I couldn't find EMT anywhere). I'm not sure if EMT is just not advertised (like other fittings, e.g. straps or plastic bushings) or if this particular one just doesn't work with EMT (if so, where can I find a 3/4" bushing that does?). I wasn't able to find its UL listing to confirm how it was tested.

Is this the right part? Am I using it wrong?

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    Much of the excitement about grounding bushings seen on this forum is over cases where they need not and should not be used at all. To a notably plastic Tesla enclosure, simply run a ground wire. If your conduit path is EMT from the panel, then run the ground from the Tesla EVSE to the nearest junction box. If a conduit body could become a junction box for the purpose of supplying a nearby ground screw location, that's fine. Apr 29, 2023 at 7:26
  • EMT fittings for boxes use the same threading as RMC or IMC conduit does.
    – Ecnerwal
    Apr 29, 2023 at 14:24
  • @Ecnerwal EMT seems to use non-tapered threading while RMC/IMC use tapered threading - see my answer here.
    – Armand
    Apr 29, 2023 at 17:35
  • @Harper I was trying it based on your recommendation in the other answer. In any case, I already ran a separate ground wire for this connection, but I'm trying to understand whether it's even a suitable tool for this EMT run and if I was using it correctly. If not, what job is it right for, and how should it be used correctly there?
    – peter
    Apr 29, 2023 at 18:05

1 Answer 1

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According to the info below, since your EMT connector presumably comes with a locknut, you would need to use that first under this bushing, as the bushing can not be used as the means to secure the tubing to the enclosure.

Normally, since Rigid/IMC are threaded and EMT is not, fittings are labeled for one or the other. In this case, a Rigid/IMC grounding bushing should also be suitable for use with a threaded EMT connector (an "other threaded fitting"), as although the bushing seems to be straight threaded (see drawing below of similar bushing) and not tapered, it has a set screw. My understanding is that without a locknut, set screw or other securing device, at least one of the two joined threaded pieces needs to have tapered threading in order to make the connection mechanically secure. EMT fittings (according to info below) are normally straight threaded

A useful summary of info on threaded Rigid, IMC and EMT fittings and connection from the Steel Tube Institute:

Fittings for Use with RMC, IMC and EMT

Threaded fittings

Threaded joints, both fitting to conduit and fitting to threaded integral box entries, shall be made up wrench tight.

NOTE: Avoid excessive force. Generally a force equivalent to hand tight plus one full turn with an appropriate tool is recommended. This should ensure engagement of at least three full threads.

Conduit bodies generally have an integral bushing to provide a smooth surface for conductors when pulled. This bushing is often mistaken for a conduit end stop. It is not necessary that the conduit be inserted flush against this bushing to assure a secure joint.

Properly align the raceway, fittings and knockouts to provide secure mechanical and electrical connections. Allow sufficient conduit length to complete engagement of the conduit and fittings at joints and entries.

Conduit bushings shall not be used to secure threaded RMC or IMC to a box or enclosure. A locknut shall always be assembled between a conduit bushing and the inside of the box or enclosure.

EMT connectors are permitted to be assembled into threaded entries of boxes, conduit bodies or internally threaded fittings having tapered threads (NPT). EMT fittings designed to NEMA FB 1, “Fittings, Cast Metal Boxes, and Conduit Bodies for Conduit and Cable Assemblies,” have straight threads (NPS). Threaded openings where these fittings are intended to be used are permitted to have either tapered (NPT) or straight (NPS) threads. Care should be taken to ensure that the threaded entry will accommodate a minimum of three full engaged threads of the fitting.

Where a locknut is provided with a fitting as the means of securement to a box or enclosure, the locknut is to be secured by hand-tightening to the enclosure plus 1/4 turn using an appropriate tool.

NOTE: While securing the locknut, take care to avoid excessive pressure when gripping the body of the fitting is necessary.

Do not rely upon locknuts to penetrate nonconductive coatings on enclosures. Coatings shall be removed in the locknut contact area prior to raceway assembly to ensure that a continuous ground path is achieved. Touch up bare area as needed after installation.

Sample grounding bushing specs (note straight threading): enter image description here

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  • This is useful info but doesn't help me with my questions. My main question is whether the grounding bushing attached is the right one for EMT (thread compatibility can be one part of this), and if so, how do people use it / fit it in plastic boxes.
    – peter
    Apr 29, 2023 at 18:02
  • @peter Answer edited - yes, bushing seems correct as long as EMT connector's locknut is first used underneath it.
    – Armand
    Apr 29, 2023 at 18:23
  • Thanks! This helps answer my question on "is it compatible with EMT" :) Do you have any insight on the "how to fit it in a box" part, or where this can be used?
    – peter
    Apr 29, 2023 at 19:25
  • @peter It fits where it fits; as Harper noted your charger box may be too small for such a bushing and may need an incoming ground wire instead. Such bushings seem to normally be used with larger diameter rigid/imc for larger-gauge wires where a simple clamp to box does not provide enough of an electrical connection by Code or situations where conduit is being used for protection of exterior wires entering conduit without a junction box (e.g. wires from solar panel).
    – Armand
    Apr 29, 2023 at 21:06

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