Short answer: mount the ground bar on the enclosure wall, low and beside the cable entries, and bond the mounting plate to it with a dedicated green jumper — 10 AWG copper for a 60 A panel — under conical star washers on at least one 1/4 in (6 mm) stud. Keep every drilled hole inside the gasket line, and the box keeps its sealing.
The code cares about the bond between wall and plate, not about which surface holds the bar, so you choose on wiring and corrosion grounds. If your reason for asking is plate room, the wall bar gives it back: incoming grounds land within about 6 in (150 mm) of the glands, and the green wiring stays off your backplate.
The two locations side by side
Both placements turn up in working panels every week. What separates them is where the green wire runs and which surface you have to drill. Two rows below — wall penetrations and corrosion — decide the rating story, so weigh them first.
| Decision | Bar on the enclosure wall | Bar on the mounting plate |
|---|---|---|
| Incoming ground conductors | Land 4-6 in (100-150 mm) from the gland cluster | Run from the entries up to the plate first |
| Grounds to devices | Cross from the plate to the wall, 6-20 in each | Stay on the plate, typically 6-12 in (150-300 mm) for devices near the bar |
| Holes in the sealed wall | 2 stud holes, best bought as factory cutouts | None; the removable plate comes out for bench drilling |
| Corrosion exposure | Studs pierce the wet outside wall | Plate studs sit dry inside the box |
| Plate space | Whole backplate stays free | Bar takes a strip 1-2 in wide |
| Bond still needed | Green jumper, bar to plate stud | Green jumper, plate to wall |
| Best fit | Sealed washdown boxes with mostly incoming feeds | Large panels where most grounds land on devices |
Whichever column you pick, the bond between wall and plate is the part the code sizes. The worked example below takes it end to end.
Where the wall bar wins
Sealed washdown and outdoor stainless boxes are the wall bar's home ground. Cable entries cluster at the bottom of the wall, and in a small panel the incoming equipment grounding conductors outnumber the device grounds. A bar 4-6 in (100-150 mm) above the gland cluster lets each incoming ground land almost where it enters, and the whole backplate stays free for DIN rail.
The catch is the wall. Stainless shrugs off washdown, but every field-drilled hole adds swarf and a crevice where chlorides settle. The clean way is to buy the holes: custom enclosures where you set every cutout are built to your drawing in 304 or 316L where salt air or brine calls for it, bar holes cut inside the gasket line, delivered in 10 business days from your approval of the drawing. The studs arrive sealed, with the rating untouched.
If a hole has to be field-cut anyway, power down and check for absence of voltage first, then follow how to cut a hole in a stainless steel enclosure before you seat the stud.
Where the plate bar wins
Panels whose grounds belong to mounted devices — power supply, drive, PLC, filter — favor the plate. A bar along the bottom or side edge keeps each component ground 6-12 in (150-300 mm) long and gives every device one shared reference point. Plenty of builders treat the plate as the default and move the bar only for a reason.
Service is the second argument: the plate lifts out with the bar still landed, and the grounds stay attached while you work.
Painted carbon steel settles the indoor case. NEC 250.12 strips paint, lacquer and enamel from grounding contact surfaces, and a drilled coated wall invites rust under the coating. Take the plate out, drill it on the bench, and bond plate to wall with a jumper instead.
Big builds split the difference: a wall bar at the entries for incoming grounds, ground terminal blocks along the rail for control wiring. The bar-versus-bonded-backplane trade gets its own treatment in backplane bonding vs ground bar in control cabinets.
Sizing the wall-to-plate jumper for a 16 x 12 x 8 in box at 60 A
The jumper is the part the code sizes, so here it is worked end to end. Every input is either catalog geometry or a labeled assumption; replace the assumptions with your own breaker and fault figures before cutting wire.
The inputs
- Box: 16 x 12 x 8 in (H x W x D) stainless wall-mount — a mid-range size on our line, where outside sizes run 6 x 4 x 4 in to 60 x 36 x 16 in.
- Largest overcurrent device ahead: a 60 A breaker (assumption — swap in your own rating).
- Available fault current at the feeder: 10 kA (assumption — use the figure for your upstream gear).
- Jumper route: bar at the bottom of the back wall to the nearest plate stud, 6 in (150 mm).
The rule
NEC Table 250.122 sizes an equipment grounding conductor from the rating of the overcurrent device ahead of it. The wall-to-plate jumper is the grounding conductor for the plate, so it takes the same size: 60 A calls for 10 AWG copper.
The arithmetic
10 AWG copper resists about 1.0 Ω per 1000 ft [3.3 mΩ per m] at 20 °C. A 6 in run works out to 1.0 Ω x 6/12,000 = 0.0005 Ω, or 0.5 mΩ. At a 10 kA fault the jumper drops 10,000 A x 0.0005 Ω = 5 V along its length. Heat the copper 100 K inside that fault and resistance rises 39 %, because copper climbs about 0.39 % per K: 0.5 mΩ becomes 0.7 mΩ, still a rounding error in the fault path. The washer joints sit on bare metal and add less than the wire does, so the jumper sets the number.
The decision
Land 10 AWG green stranded copper from the bar to a 1/4 in plate stud, conical star washer under lug and nut at each end. Step the size with the breaker ahead of the panel:
| Largest device ahead | Copper jumper (NEC Table 250.122) |
|---|---|
| 20 A | 12 AWG (3.3 mm²) |
| 60 A | 10 AWG (5.3 mm²) |
| 100 A | 8 AWG (8.4 mm²) |
| 200 A | 6 AWG (13.3 mm²) |
Above 60 A of protection the jumper steps up with the table rather than with judgment. The same table sizes every ground landing on the bar, so the jumper ends up at least as large as anything it serves.
The bond the code asks for
Three parts of the NEC govern the joint, and all three are about metal, not geography.
NEC 250.4(A)(5) makes fault current return over metal: the earth is not part of the effective ground-fault current path. 'It is all steel anyway' is not a bond; wall and plate need a deliberate one.
NEC 250.96(A) requires metal parts serving as equipment grounding conductors to be bonded together so they can carry the fault current likely imposed on them. Raceways, cables, enclosures and your mounting plate all count.
NEC 250.12 strips paint, lacquer and enamel from threads and contact surfaces at grounding connections. On a powder-coated box that means removing the coat under each lug, or letting conical star washers bite through to bare metal. On stainless it means clean, swarf-free contact.
Color is fixed too: NEC 250.119 reserves green, or green with a yellow stripe, for insulated conductors 6 AWG and smaller — your jumper included.
Panels get listed to UL 508A, the standard for industrial control panels; the shape is the same, with enclosure, plate and grounding terminations forming one bonded system wherever the bar sits.
A plate on welded studs takes conical washers under its mounting nuts, and adding the green jumper at one stud makes the bond deliberate instead of incidental. Fault current follows clean metal — the same reason welding return paths require a dedicated low-resistance bond. The grounding and bonding guide carries the electrode-and-bonding basics this article skips.
Keeping the NEMA 4X sealing while the studs go through the wall
Every stud through a sealed wall is a penetration, and the weakest penetration sets the assembly rating. Two 1/4 in studs with sealing washers hold the Type 4X sealing; one unsealed field hole throws it away.
Our wall-mount boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed. Keep that rating by placing each hole inside the gasket line — on the back or side wall, clear of the door flange — and by sealing every hole you add yourself.
A hole that lands in the wrong spot gets rescued in how to seal a wrongly drilled hole in an enclosure. Studs and screws through the wall, and what they do to a Type 4 rating, are worked through in screws through a control panel wall and the Type 4 rating. Wash the swarf off and passivate after cutting, because carbon-steel residue stains stainless around fresh holes; corrosion prevention inside an outdoor stainless enclosure covers the rinse routine. Once devices mount to plate and wall, the rating picture changes again — what NEMA rating a panel keeps after you cut it and mount devices walks that case.
The decision by build
Pick the location from where the grounds live, then buy the holes instead of drilling them:
| Build | Bar location | Bond to specify |
|---|---|---|
| Washdown or outdoor stainless, 60 A or less | Wall, low beside the glands, holes as factory cutouts | 10 AWG green jumper, conical washers, 1/4 in stud |
| Salt air, brine or chemical spray | 316L box, wall bar | Same jumper rule, sized from NEC Table 250.122 |
| Indoor painted steel, Type 12 | Plate | Plate-to-wall jumper, bare contact metal per NEC 250.12 |
| Large panel, most grounds on devices | Plate, or wall bar plus rail ground blocks | Bond plate to wall either way |
On the order for the washdown case: a 304 or 316L wall-mount box at your size, two 1/4 in bar-stud holes specified as cutouts low on the back wall inside the gasket line, gland cluster drawn where the cables arrive, delivered in 10 business days from your approval of the drawing. The stainless size finder filters the standard lines by size and grade; custom work takes any size between them.
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 |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 304 stainless | 16 x 14 x 8 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 |
Questions
Is a ground bar on the enclosure wall acceptable instead of the mounting plate?
Yes. NEC 250.96(A) asks for the wall and the plate to be bonded into one fault path; once a jumper connects them, either surface can hold the bar. Size the jumper from NEC Table 250.122 — 12 AWG copper for a 20 A panel, 10 AWG for 60 A — and put conical star washers under both lugs. From there the location is a wiring choice, not a code one.
What size jumper bonds the mounting plate to the enclosure wall?
Size it from NEC Table 250.122 for the largest overcurrent device ahead of the panel: 12 AWG at 20 A, 10 AWG at 60 A, 8 AWG at 100 A, 6 AWG at 200 A. A 6 in (150 mm) 10 AWG jumper adds about 0.5 milliohm, so the wire sets the path resistance and a clean washer joint adds little.
Do conical star washers alone satisfy the bond, or is a wire jumper needed?
Use both. A conical star washer bites through paint or oxide to give NEC 250.12 its bare contact metal and locks the joint against vibration. The washers are the supplement; the dedicated green jumper carries the fault current. On a 1/4 in stud, stack washer, lug, washer, nut in that order.
Can DIN-rail ground terminal blocks replace a ground bar?
For control and analog wiring, yes: ground terminal blocks that clamp onto the DIN rail put a ground point next to every terminal group and keep shield tails short. They do not replace the bond — run one green jumper from the rail to the bar or a plate stud, sized for the largest feeder EGC, so the rail itself is grounded.
Will a stainless enclosure rust around a drilled ground-bar hole?
Not through the base metal, but two things stain it: carbon-steel swarf left in a fresh hole, and chloride wash-down. 304 pits under chloride deposits in crevices even at room temperature, and chloride stress cracking starts near 60 °C (140 °F) in 304 and 316L alike. Deburr, passivate and rinse after drilling; in salt air or brine, order 316L.
