Bonding a metal receptacle junction box to the equipment ground

Short answer: yes. Give the steel box its own bond: a green 10-32 grounding screw with a pigtail spliced into the circuit's equipment grounding conductors (EGC). Give the receptacle a second pigtail off the same splice. The NEC requires a connection between the metal box and the grounding conductors in it, and that connection serves no other purpose. The path through the receptacle's ground pin does not count as the box bond, because it leaves with the device at the first service call. The EMT riser above the slab carries its own continuity through listed fittings; the wire EGC still lands on the box screw. The parts, six steps, the worked numbers for a 20 A, 120 V receptacle box, and the resistance check that proves the bond follow.

Why the ground pin is not a box bond

The NEC requires every metal box to be connected to the EGCs of the circuits in it, by a connection that serves no other purpose. A bond that rides on the receptacle fails on both counts: it lives only while the device is installed, and its first job is the device. The code pairs two duties in one box. A grounding-type receptacle in a metal box gets its grounding terminal connected to the box or the EGC splice, and the box gets its own connection to the EGC. Two pigtails off one splice cover both.

One case skips the screw: a wire-type EGC that only passes through a box, with no splice and no device, need not touch the box. That is a true pull box. Splice one conductor or mount one receptacle, and the connection becomes part of the work. A box where circuits land, grounds splice and a receptacle mounts is a junction box, so the green screw goes in. The same splice-and-screw pattern lands a motor frame ground; the grounding a motor junction box with the motor ground wire article shows that version.

The PVC-to-EMT change at the slab alters the raceway, not the grounding plan. Pull the wire EGC with the circuit from panel to box and land it there. The raceway's fittings carry their own continuity in parallel, and the wire bond stands even when a fitting works loose. On a 480 V circuit the EMT ends also take bonding bushings; the bond bushing requirements for EMT raceways page sets out when and where. The enclosure grounding and bonding guide works through the fault path behind these rules, and the grounding conductor entry article matches the entry connector to the wall opening.

What you need

• One green 10-32 grounding screw per box. Metal boxes carry at least one hole tapped 10-32 for it, and the hole often wears a green paint daub from the factory.
• Two green pigtails per box, 6 in [150 mm] each, sized like the EGC. NEC 250.119 requires insulated EGCs of 6 AWG and smaller to be green or green with yellow stripes.
• Wire connectors sized to the ground splice, a driver, an ohmmeter, a receptacle tester, and a lockout device for the breaker.

The breaker ahead of the circuit sets the wire size:

The tapped-screw method is a permitted connection for 10 AWG and smaller, so it covers the top three rows. For thread engagement and lug fit on thin walls, the grounding screw threads and lug fit article carries the numbers.

Bonding the box and the receptacle

1. Lock out and prove dead. Open the breaker, lock it, and check for absence of voltage with a meter before the box opens.
2. Bring the wire EGC in. The raceway turns from PVC to EMT at the slab; the wire EGC stays with the circuit all the way to the box.
3. Splice the grounds. Join every EGC under one wire connector — two branch circuits mean two EGCs — and add one 6 in [150 mm] green pigtail.
4. Bond the box. Wrap that pigtail clockwise under the green 10-32 screw and drive it into the tapped hole. That screw carries its pigtail and nothing else.
5. Bond the receptacle. Add a second 6 in [150 mm] pigtail from the same splice to the receptacle's green ground screw. Both pigtails match the EGC size in the table.
6. Close and test. Fold the pigtails clear of the terminals, fit the device and cover, restore power, then run the checks below.

Bonding a 20 A, 120 V receptacle box on an EMT riser

The inputs, each with its source:

• 20 A, 120 V receptacle circuit, PVC below the slab turning to EMT above — the case the steps wire up.
• 20 A breaker: NEC Table 250.122 assigns a 12 AWG copper EGC, so both pigtails are 12 AWG.
• Steel box with one tapped 10-32 hole, standard on metal boxes.
• Two 6 in [150 mm] pigtails of green 12 AWG, the assumed reach from a center splice to screw and terminal.
• 12 AWG copper resistance of about 1.6 Ω per 1000 ft at 20 °C.

The rule in words: a wire's resistance is resistance per foot times length, and the voltage a fault drops across it is current times resistance.

The arithmetic:

• One pigtail: 0.5 ft × 1.6 Ω/1000 ft = 0.0008 Ω, or 0.8 milliohm.
• A fault at the receptacle's ground pin drives current through the pigtail in series with the 12 AWG EGC back to the panel.
• At an illustrative 500 A fault: 500 A × 0.0008 Ω = 0.4 V across the pigtail. Warm the copper to 75 °C and it gains 0.39 % per K over 55 K, about 21 %, still close to a milliohm.

The result: two pigtails put 0.8 milliohm in each path, and even a worst-case series pair costs 1.6 milliohms — under half a volt at 500 A.

The decision: any box on a breaker up to 20 A takes 12 AWG pigtails under the green 10-32 screw. Scale with the table: 60 A takes 10 AWG, 100 A takes 8 AWG on a listed connector. Prove the bond by resistance. A 100 ft [30 m] run of 12 AWG EGC reads 1.6 Ω/1000 ft × 0.1 = 0.16 Ω; the two pigtails add 0.0016 Ω. The box-to-panel meter lands near 0.16 Ω. Over 1 Ω on that run means a missed or corroded bond, so redo the splice.

Checks when done

• Ohmmeter from box wall to the panel's ground bar, power off: near 0.16 Ω for a 100 ft [30 m] run of 12 AWG, plus about 0.16 Ω for each extra 100 ft.
• Receptacle tester in each receptacle after power returns: it reads correct ground, not open ground.
• A firm tug on each pigtail before closing: the connector grips and the screw stays put.
• One look at the green screw: its pigtail alone sits under it.

Mistakes that cost the bond

• Letting the receptacle be the only ground. The first device swap leaves the box floating; the two-pigtail layout removes that dependency.
• Sharing the green screw. One screw takes one pigtail; everything else splices in the wire connector.
• Bonding through paint. NEC 250.12 requires paint, lacquer and enamel off the threads and contact surfaces unless the fitting is made to bite through. On a coated box, sand the lug spot to bare metal.
• Splicing grounds outside a box. Every EGC splice sits inside an accessible box with its cover on.
• Dropping the wire EGC at the raceway change. The EMT path runs in parallel; the wire bond at the box is the one you can measure, so keep both.

Ordering a steel box for the same circuit

A panel-grade steel box bonds by the same rules, and a custom one starts with the drawing. Mark the bond point, the EMT entries and the conductor fill on the layout you send. The cutout drawing checklist on the custom stainless enclosures page keeps those calls together, and the custom enclosure builder takes your material, size and every cutout, built from one piece. Custom work counts the 10 business days from your approval of the drawing. Inside a larger cabinet, the enclosure-to-ground-bus article covers the bus side, and the fittings and knockouts article for a steel drive enclosure shows where entries land.

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.

Questions