Run 6 AWG copper, take it out low on the wall, and seal it with outdoor silicone - that is the whole job. The route out is a listed termination, a short nipple, or a clean 0.25 in [6 mm] hole with a bushing. Duct seal is the wrong material here: it is a conduit putty that never cures, and heat plus gravity move it within a few summers. Size the wire before you drill, because the NEC requires grounding electrode conductors of 8 AWG and smaller to ride in a raceway. One point to settle now: the added rod is an auxiliary electrode under NEC 250.54, so the equipment grounding conductor already in the feed stays in place.
Why 6 AWG copper is the size to buy
Start with the conductor, because its size decides whether you need conduit at all. The NEC allows a grounding electrode conductor of 8 AWG or smaller to run only inside a raceway: conduit, EMT, or the armor of the cable. From 6 AWG copper upward you can run it exposed, fastened to the wall, anywhere it stays clear of physical damage. Copper is the practical outdoor choice; the NEC keeps aluminum grounding electrode conductors at least 18 in [457 mm] above the earth, and a rod clamp sits right in that zone.
Rod, pipe and plate electrodes cap out low. To any of the three, the NEC asks for no more than 6 AWG copper or 4 AWG aluminum, so that one size is both the smallest conductor that runs open and the largest this electrode can demand. Plan for no splice: the code accepts only irreversible compression splices and exothermic welds, so order one length. At the electrode, land the wire with a listed clamp, a listed lug, a listed pressure connector, or an exothermic weld - the four methods the code names.
What the added rod does for you
Your box is already bonded by the equipment grounding conductor in the feed, and that is the wire that clears a fault. The earth is not an effective ground-fault current path - that is the NEC 250.4(A)(5) framing - so soil cannot trip your breaker. What the rod buys you is a local earth reference. Connect it to the equipment grounding conductor, as NEC 250.54 permits for an auxiliary electrode. Your surge protector then gets a short, straight route that dumps surge current close to where it arrives.
Leave the feed alone. The equipment grounding conductor is sized from the overcurrent device ahead of it using NEC Table 250.122: at 60 A that is 10 AWG copper, and it stays that size with or without the rod. For the inside-the-box half of the job - buses, lugs, bonding the plate - the grounding and bonding guide walks the whole panel.
Three ways through the wall
Four honest routes exist, and the hole follows the route. For the two that mount a fitting, a 1/2 in trade-size knockout is 0.875 in [22 mm] across, the dimension UL 50's knockout table (Table 71-1) sets for fittings in that size.
| Route out | Hole it needs | Conductor it suits | Sealing |
|---|---|---|---|
| Listed grounding-electrode termination, which clamps the conductor and mounts in a knockout | 1/2 in knockout, 0.875 in [22 mm] | the range marked on the fitting | silicone at the edge and threads |
| 1/2 in metal nipple, locknut outside and in, bushing inside | 0.875 in [22 mm] | any size; the NEC's route for 8 AWG and smaller | silicone under both locknuts |
| Small cord grip on the insulated conductor | threaded hole to the grip's own marking | insulated, about 0.27 in [7 mm] OD | the grip's own gasket and seal |
| Drilled hole with a bushing | 0.25 in [6 mm] bare; 0.31 in [8 mm] insulated | bare or insulated only | silicone, tooled on both faces |
A clamp made for jacketed building cable is the odd one out. It wants the same 0.875 in [22 mm] knockout, and its grommet grips a cable jacket, leaving a single loose conductor with nothing pressing on it. For hole and knockout dimensions across the fitting range, the cord grip knockout sizes article carries the tables, and the enclosure entry connector and bond article covers the bonding at the point of entry.
Where the hole goes
Water decides where your hole goes. Prefer the bottom wall, then the low side wall, and leave the top face alone. Work on the body of the box, on the flat, clear of the gasket channel, the drip edge above the door, the welded corners and the mounting feet. Run the conductor downward outside so rain tracks away from the penetration, and strap it flat to the wall. Where the run crosses a walkway or a hedge line, sleeve that stretch in conduit; the open-run allowance for your conductor ends where physical damage begins.
What you need
- One length of 6 AWG bare copper, long enough to reach the rod with no splice
- Step bit: 0.25 in [6 mm] for bare wire, 0.31 in [8 mm] for insulated
- Deburring countersink, or a bit one size larger
- Nylon bushing, or your chosen fitting with its locknuts
- Neutral-cure silicone sealant
- Listed clamp for the rod, rated for direct burial if it ends up covered
- A meter, for the checks at the end
Drill, land and seal
Lock out the disconnect and confirm the circuit is dead before you open the door; everything below is de-energized work.
- Mark the spot on the bottom or a low side wall, on the flat, clear of the gasket channel and corners, and center-punch it.
- Drill slow with a step bit and a drop of cutting oil - 0.25 in [6 mm] for the bare conductor, 0.31 in [8 mm] for insulated - then deburr both faces with a countersink.
- Seat the bushing, the listed termination, or the nipple with its locknuts. On a painted box, scrape the metal parts of the ground path to bare metal where they contact, since NEC 250.12 requires paint off the contact surfaces of grounding connections.
- Land the inside end on the ground bus or the enclosure ground stud, in a listed lug marked for that size.
- Route the conductor straight down the wall, strapped, to the rod; short and direct serves your surge protector best.
- Clamp it to the rod with a connector listed for the electrode, rated for direct burial where it sits under soil.
- Seal with a bead of neutral-cure silicone around the conductor and the bushing lip, inside and out, tooled smooth before it skins. Silicone as a material spans about -60 to 200 C in typical O-ring handbook values, so summer wall heat sits well inside its range. Give the bead a day to cure before the hose test.
Worked example: 60 A condenser disconnect on a 10 x 8 x 4 in box
The case: a 60 A air-conditioning disconnect feeding a condenser, a surge protector going in beside it, and one ground rod by the pad. The enclosure is a 10 x 8 x 4 in (H x W x D) 304 stainless wall-mount box, rated NEMA 4X / IP66 by the manufacturer and not UL listed.
Inputs, each with its source:
- Overcurrent rating: 60 A, from the disconnect label.
- Equipment grounding conductor in the feed: 10 AWG copper, from NEC Table 250.122 at 60 A.
- Electrode: one rod, so the copper cap applies.
- Conductor: bare 6 AWG copper, 0.162 in [4.11 mm] across - the standard AWG dimension.
- Hole: 0.25 in [6.35 mm].
The rule in words: below that size you would need a raceway, and above it the rod gains nothing, so 6 AWG is the answer before the drill turns.
The arithmetic: 6.35 mm hole minus 4.11 mm conductor leaves 2.24 mm of clearance, a sealant ring about 1.1 mm thick all round once tooled. That ring is small enough to fill solid with silicone, and tight enough that putty would spend years of heat cycles fighting to stay in it.
The decision: drill 1/4 in, deburr, bush, and bead silicone on both faces. Switching to insulated green conductor at about 0.27 in [6.9 mm] OD moves you to a 0.31 in [7.9 mm] bit, and 7.9 minus 6.9 leaves 1.0 mm of clearance. Near salt air or a washdown hose, build the same panel in the 316L version of this size.
Checks when you are done
- Continuity: zero your meter leads, then read from the ground bus to the rod clamp; under 1 Ω end to end says the path is intact.
- Earth resistance: a driven rod should measure 25 Ω or less to earth. Above that, the fix is a second full-length rod at least 6 ft [1.8 m] from the first.
- Weather: hit the penetration with a hard garden-jet spray for a minute, open the door, and look for tracks. A dry wall around the bushing says the bead is doing its job.
Factory holes beat field holes
Building this panel new? Order the penetration with the box. The cutout designer lays the hole or the gland mount on any face, checks its spacing against the gasket and the corners, and exports the layout. The box is delivered in 10 business days, counted from your approval of the drawing. Keep the rating in perspective either way: a box rated NEMA 4X / IP66 by the manufacturer carries no UL listing, so the rating describes the assembly as built. A drilled hole's weather protection is the seal you make, while a listed gland or termination brings its own rating - which is why those rows sit at the top of the table. The custom stainless enclosures page shows what a drawing-based order involves, and what a panel keeps after you cut it covers field work in full.
Mistakes that cost you the seal
- Duct seal as the weather seal. It stays putty for life, and wall heat softens it until gravity wins. Pack conduit bodies with it; seal enclosure walls with silicone.
- A hole on the top face. Rain wetting the wall channels water along the wire into the box, so drill low and run down.
- A raw drilled edge. The burr saws at insulation over years of wind sway; deburr both faces and fit a bushing.
- Silicone on a dirty hole. Wipe with solvent, let it flash off, then bead and tool.
- Pulling the equipment ground because a rod appeared. Soil clears no faults under NEC 250.4(A)(5); the conductor in the feed is the one that trips the breaker.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 10 × 8 × 4 in | 304 stainless | 10 x 8 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 10 × 8 × 4 in | 316L stainless | 10 x 8 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Is duct seal waterproof enough for a hole in an outdoor enclosure?
No. Duct seal is a conduit putty made for blocking air and debris; it never cures, and enclosure-wall heat softens it until it sags out of the gap. For a 0.25 in [6 mm] hole around a bare grounding electrode conductor, tool a bead of neutral-cure silicone inside and out, and give it a day to cure before it sees rain.
Can an 8 AWG ground wire leave the enclosure without conduit?
It needs a raceway: the NEC allows 8 AWG and smaller grounding electrode conductors to run only inside conduit, EMT or cable armor. From 6 AWG copper upward you can run exposed, fastened to the wall, where it stays protected from damage, and a rod, pipe or plate electrode tops out at that size anyway.
Do I need a listed connector where the ground wire leaves the box?
The clean route is a listed grounding-electrode termination or a 1/2 in metal nipple with locknuts and a bushing, both mounting in a 0.875 in [22 mm] knockout. A plain 0.25 in [6 mm] deburred hole with a bushing is fine for the bare conductor, which is 0.162 in [4.1 mm] across. Clamps made for jacketed building cable want the big knockout and grip a jacket, with a loose conductor swimming in them.
Does the new ground rod replace the equipment ground in the feed?
No, soil clears no faults. Under NEC 250.4(A)(5) the earth is not an effective ground-fault current path, so the equipment grounding conductor in the feed stays; at 60 A that is 10 AWG copper from Table 250.122. The added rod is an auxiliary electrode under NEC 250.54: connect it alongside the equipment ground and keep the wire that trips the breaker.
