Short answer: let the EMT carry the fault current, bond every metal box through its listed connector, and bond each receptacle to its box with a 10-32 green ground screw engaging two full threads plus a pigtail, or use a listed self-grounding receptacle instead. In a flush box, the 6-32 device mounting screws do not count as the bond. The NEC sizes the pigtail from the breaker — 12 AWG copper on a 20 A circuit — and wants bare steel under every bonding contact.
Does EMT count as an equipment grounding conductor?
Yes: the NEC lists steel electrical metallic tubing among the raceways that may serve as the equipment grounding conductor, so with listed fittings at every box you need no separate wire EGC to satisfy the grounding rules.
The tube is thin-wall steel joined by set-screw or compression fittings, and listed fittings count as bonding means. Steel-on-steel contact at every joint carries fault current from box to box and back to the panel. A wire EGC stays optional: pull one when the specification asks for it or when you want a visible conductor, and NEC Table 250.122 then sizes it from the rating of the breaker or fuse ahead of the circuit. Most flush runs hide the raceway behind drywall, so every joint you tighten at rough-in is a joint nobody revisits. The grounding and bonding guide traces the full fault path the raceway completes.
What bonds the metal box to the EMT?
The listed EMT connector or coupling makes that bond: its set screws or compression ring bite bare steel on both the tube and the box wall, and the NEC requires every metal box in the run to be connected to the grounding path.
Set-screw fittings grip a steel thimble inside the tube; compression fittings clamp a ferrule over it. Either style is a listed bonding means, so a standard metal junction box needs no extra screw to join the grounding path. Tighten the set screws hard: a loose one is the most common open in an EMT system and shows up as flickering meter readings long before it shows up as a fault. When you pull a wire EGC and splice or terminate it in the box, the NEC requires the box to be connected to that conductor as well; bonding a metal receptacle junction box to the equipment ground covers the wire-to-box methods.
When the enclosure is a custom stainless box rather than a stamped junction box, the same fitting does the bond. We cut the entry holes to your drawing, so put them on the drawing as factory cutouts for a custom stainless enclosure instead of drilling on site; the type rating you specify for such an enclosure is a manufacturer rating, not UL listed. The EMT, PVC and cable entry options for an enclosure are set out in the wiring-methods article.
Which screw bonds a device or a pigtail to the box?
Use the 10-32 green ground screw with the square washer under its head: the NEC's bonding rules accept any machine screw that engages at least two full threads or is secured with a nut, and neither green paint nor a listing is demanded.
US steel boxes come with a tapped 10-32 hole in the back or on a side. At 32 threads per inch, two full threads engage 2/32 in = 1/16 in [1.6 mm] of steel, and the supplied screw is chosen to meet that minimum in the wall it goes into. The green enamel is convention; the captive square washer is what spreads the clamp over a clean ring of metal. NEC 250.12 requires paint, lacquer and enamel to be removed from threads and contact surfaces at grounding and bonding connections, so brighten a coated hole until bare steel shows, then drive the screw.
For replacement hardware, the 10-32 thread runs through US boxes, covers and fittings; the 10-32 cover screw specifications page lists thread, length and head details when you need to match a supply. Grounding screws and lugs inside enclosures follow the same two-thread logic; enclosure grounding screw threads and lug fit extends the check to lug terminals.
Do receptacle mounting screws count as the bond in a flush box?
In a box recessed in the wall they do not: the NEC's receptacle bonding rules accept a wire pigtail or a listed self-grounding receptacle, and the two 6-32 yoke screws count there only as fasteners.
Yoke-screw contact wins only where the box mounts on the wall surface and the yoke presses directly onto it. Recessed in drywall, the strap floats between box ears and yoke, and paint, zinc plating and thread fit stand in the current path. The two clean answers are a pigtail landed on the receptacle's green ground terminal, or a listed self-grounding receptacle whose spring clip on the yoke grips the box edge and makes the bond without any wire. Self-grounding devices cost little, install in the same minutes, and skip one splice.
Are switches, plaster rings and raised covers bonded the same way?
A switch is bonded when you fasten it with its metal screws to a metal box or to a metal cover connected to an equipment grounding conductor, and a plaster ring or raised cover is bonded by its 8-32 screws where the flats seat tight on the box.
Metal screws into metal are the connection; a plastic device strap changes nothing. A plaster ring adds one layer, and its two 8-32 screws carry the bond while the flats bear tight on the box face. Raised covers bond the same way when they have those flats. Legacy covers with long, roughly 3/4 in [19 mm] screws and no flats sit proud of the box, so give them their own green screw and a short jumper from the box. The logic scales to bigger hardware: control panel door bonding covers jumper size, routing and the pull test on panel doors and spacers.
How do you bond a receptacle in a flush box step by step?
De-energize the circuit and verify absence of voltage first; then one splice, one green screw and one device terminal bond the whole assembly in about five minutes per box.
You need a green 10-32 ground screw with its washer, pigtails sized to the circuit, a wire connector and a screwdriver. NEC Table 250.122 sets the pigtail size from the breaker: 12 AWG copper on a 20 A circuit.
- Set the pigtails. With a wire EGC in the box, join the EGC, a box pigtail and a device pigtail under one wire connector. With raceway-only grounding, the fitting already bonds the box, so one device pigtail under the green screw does the rest.
- Clear the contact. Bare steel must sit under the washer; leave a factory-tapped hole alone and brighten a coated one until metal shows.
- Drive the screw. Bottom the green 10-32 screw so engagement passes the two-thread, 1/16 in [1.6 mm] minimum.
- Land the device pigtail on the receptacle's green ground terminal and tug it.
- Dress the wires off the strap and close the box.
Worked example: a 120 V, 20 A receptacle circuit on a raceway-only EMT run, in a flush 4 in square steel device box. The fitting bonds the box, and the pigtail from the box's green screw to the receptacle's ground terminal is 12 AWG copper, because NEC Table 250.122 sets the wire size from the 20 A breaker. The tapped hole is 10-32, and 32 threads per inch makes two full threads equal 2/32 in = 0.0625 in = 1/16 in [1.6 mm] of engaged steel; on a wall too thin for two threads, run the screw through and pull it up with a nut behind. Cut the pigtail 6 in [150 mm] long and loop it clockwise under the washer and the terminal. Trust the 6-32 yoke screws instead, and the only fault path runs through plating, paint and thread fit — exactly what the rules refuse to count.
How do you check the bond before the cover goes on?
Check three things before the cover goes on: the washer seated on bare metal, a pigtail that survives a firm tug without turning the screw, and an ohmmeter reading at or near 0 Ω from the receptacle's ground slot to the bare EMT.
Run them on every box, not only the first. Push the pigtail toward the box and pull it away; a screw that turns under hand pressure backs out later. Wiggle the raceway at the fitting while the ohmmeter stays connected, because a flickering reading is a loose set-screw you can fix now, behind open drywall. On the 20 A example circuit, the loop from panel bus to device ground slot should read a small fraction of an ohm; a reading in whole ohms means paint, plating or a loose fitting is in the path.
What mistakes cost the bond?
Four faults break most of these bonds: a coating left under the washer, a stripped 10-32 hole, an undersized pigtail, and a device bonded to an unbonded cover.
- Coating under the washer. File or scrape the hole's rim to bare steel before the screw goes in; a bonding connection wants metal, not enamel.
- A stripped 10-32 hole. The bonding rules accept a machine screw secured with a nut, so run the screw through and pull it up with a nut and lockwasher; replace the box once the thread is gone. When a ground screw snaps instead, removing a broken screw from a box walks through the extraction.
- An undersized pigtail. Match the breaker rather than the device: 12 AWG copper on the 20 A worked example, and never a size below NEC Table 250.122 for the breaker ahead.
- A device on an unbonded cover. Bond the plaster ring or raised cover first, by its flats or its own ground screw, then bond the device to the assembly.
Decide it this way: on concealed EMT, treat the raceway as the EGC, bond every box through its listed fitting, and give each grounding-type receptacle a pigtail or a self-grounding yoke; pull a wire EGC sized per NEC Table 250.122 whenever the specification asks for one, and connect it to every box where you splice or terminate it.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Is the EMT raceway or a wire the lower-impedance fault path?
The raceway. Steel EMT has a larger diameter than any wire EGC you can pull inside it, so its reactance is lower and fault current sees less impedance over the same run. Parallel bonds are intended, not a defect: the NEC wants the grounding path connected to every bonded box along the way.
What size ground pigtail suits a 15 A or a 20 A receptacle circuit?
Match the circuit EGC. NEC Table 250.122 sets the size from the overcurrent device ahead of the circuit: a 15 A breaker takes 14 AWG copper and a 20 A breaker takes 12 AWG copper. Cut the pigtail in that size; a 6 in [150 mm] length loops under the green screw without crowding the box.
Does an equipment grounding conductor that only passes through a box have to be bonded there?
Only when you splice or terminate it. The NEC requires an EGC that is spliced or terminated in a metal box to be connected to that box; a conductor passing through without a splice can run straight to its next termination. Keep the run continuous where you can, and bond at the boxes where you cut and rejoin it.
What changes in a nonmetallic box or with PVC raceway?
Plastic has nothing to bond, so the receptacle's ground terminal lands on the wire EGC alone. NEC 314.3 allows a nonmetallic box with metal raceway or metal-armored cable only when the metal parts are bonded together inside the box, so carry the wire EGC in and land it on both.
