Short answer: bond it. A grounding electrode conductor (GEC) that runs past or through a metal enclosure gets bonded to that enclosure — required where it passes through steel, good practice everywhere else. Keep the copper continuous from the neutral terminal to the electrode, and make every jumper the same size as the GEC: on a 200 A service with 4/0 aluminum entrance conductors that is a 2 AWG copper conductor, and on a 100 A service with 1/0 copper it is 6 AWG. What turns the job into a defect is a conductor cut at the bond point, a jumper smaller than the GEC, or a connection buried where nobody can inspect it.
What the grounding electrode conductor does
The GEC ties the neutral of the service disconnect to the grounding electrode system: water pipe, ground rods, building steel. Its job is voltage stabilization and a surge path, so it sizes from the entrance conductors, not from a breaker. Fault clearing is a different circuit: NEC 250.4(A)(5) calls the effective ground-fault current path the equipment grounding conductors and bonding jumpers, with the earth not considered part of it. The EGC sizes from the rating of the overcurrent device ahead of it, using NEC Table 250.122: 6 AWG copper under a 200 A breaker. The GEC on the same service is one size pair larger, because it follows the entrance conductors. The enclosure grounding and bonding guide carries the EGC side, and how the EGC differs from the plant grid at the enclosure covers the downstream landings.
Why the bond belongs on the enclosure
Lightning that lands on the service shares current through the GEC, and a wire running inside ferrous metal sees high inductive reactance at those rise times: the steel chokes the very current the conductor exists to carry. Bonding the metal to the conductor at each end shorts that loop out. On an exposed run past the box, the bond holds wire and enclosure at the same potential, so nothing arcs at the point of contact during the first microseconds of a strike. You are not adding a second GEC; you are keeping two metal surfaces from trying to spark against each other. The bond adds a parallel path and leaves the conductor intact.
Where a bond is required and where it is optional
- Through a steel wall or inside steel raceway: bond at each end with a jumper the same size as the GEC, or run one jumper of GEC size full-length inside the raceway. The raceway version has its own walk-through in bonding a ferrous raceway around a grounding electrode conductor.
- Through aluminum or stainless walls: bond it anyway with the same-size jumper. 304 and 316L stainless are essentially nonmagnetic, so the reactance penalty is small, and the lug costs minutes.
- Exposed run past the enclosure face: permitted. Land the lug around the conductor and leave the strand bundle uncut.
- Nonmetallic conduit: nothing to bond.
- Main bonding jumper: a separate part with a separate job — it lands the neutral on the enclosure — and both connections stay in place.
The same rule follows the wire into the plant. Suppose the GEC route turns one wall over from the switch and a junction box sits mid-route: a 12 x 12 x 6 in stainless wall-mount box handles the turn, ordered as 304 stainless or 316L stainless for salt and chemical areas. Order the two wall entries cut with the box; the custom enclosure builder prices every cutout from one piece. The box is delivered in 10 business days, counted from your approval of the drawing. These boxes are rated NEMA 4X / IP66 by the manufacturer; they are not UL listed. They are boxes on the GEC route, never the service equipment itself. For an outdoor pull box on the entrance route, what to specify on an outdoor service conductor pull box carries the spec sheet, and wall-mount enclosures start at 6 x 4 x 4 in.
Sizing the bond jumper for a 200 A service
Inputs. A typical case: a 200 A service whose largest entrance conductor is 4/0 aluminum (2/0 copper appears on copper-fed services), a copper GEC to the cold water pipe. The size comes from the NEC's table that pairs the grounding electrode conductor with the largest service-entrance conductor.
Rule. Every jumper that bypasses metal around the GEC is the same size as the GEC — here, 2 AWG copper.
Arithmetic. The table row for 4/0 aluminum, or 250 kcmil aluminum, calls for a 2 AWG copper GEC — 66,360 circular mils [33.6 mm²] on the standard copper tables. The 6 AWG jumper in your truck box is 26,240 cmil [13.3 mm²]: 26,240 / 66,360 = 0.40, so it carries 40% of the area and fails the same-size rule. A 4 AWG jumper, 41,740 cmil [21.2 mm²], is still only 63%.
Result. Two jumpers of GEC size, one at each wall, in lugs marked for 2 AWG.
Decision. The size moves with the entrance conductors:
| Largest entrance conductor (typical service size) | Copper GEC to the water pipe | Jumper at each wall |
|---|---|---|
| 1/0 copper (about 100 A) | 6 AWG | 6 AWG |
| 2/0 or 3/0 copper (150-200 A) | 4 AWG | 4 AWG |
| 4/0 or 250 kcmil aluminum (200 A) | 2 AWG | 2 AWG |
What you need
- Jumper wire the same size as the GEC — GEC-size copper in the worked case.
- Two grounding lugs marked for that conductor size, plus the wrench or driver to hit the lug's marked torque.
- A wire brush or abrasive pad to strip paint and oxide back to bare metal.
- A low-ohmmeter for your final reading.
- Antioxidant compound where aluminum lands on aluminum.
Installing the bond, step by step
- Trace the route from the neutral terminal to the electrode and mark every metal the conductor touches or passes through.
- At the entry wall, strip the contact patch to bare metal. NEC 250.12 requires paint, lacquer and enamel off the contact surfaces at grounding and bonding connections unless the fitting is designed to bite through.
- Land a jumper on the conductor at that wall without cutting the copper: a pressure lug around the wire or a clamp made for bonding.
- Land the other end on the enclosure's bonding boss with a lug marked for the jumper size, and torque it to the marked value.
- Repeat steps 2 through 4 at the exit wall.
- Where the route runs inside metal raceway, bond both ends of the metal or lay one jumper of GEC size full-length inside it.
- Pick the entry hardware deliberately: grounding conductor entry: connector and bond sorts connector types against wall material and conductor size.
- Keep every connection accessible for inspection — the NEC's GEC installation rules demand it — and dress the wire free of sharp bends.
Checks when the bond is done
- Ohms across each jumper: GEC-size copper runs about 0.16 Ω per 1000 ft, so a 3 ft jumper is 0.0005 Ω; zero your meter leads first and expect a near-short. A few hundredths of an ohm means paint or a loose lug seat.
- Continuity end to end: the reading from neutral terminal to water pipe matches the wire's normal resistance, never an open circuit.
- Torque at every lug, re-checked against its marked value.
- The strand bundle visible and unbroken at the bond point.
- Working space still clear: NEC 110.26(A) (2020 and 2023 editions) wants at least 3 ft of clear depth in front for 0-150 V to ground in Condition 1, 30 in of width or the equipment width, and a door that opens 90 degrees.
Mistakes that undo the bond
- Cutting the conductor to reach the wall. A cut GEC is a splice, and the NEC permits splices only with irreversible compression connectors or exothermic welding.
- Undersizing the jumper. The 6 AWG piece on the worked example's GEC carries 40% of the area and nothing more.
- Paint or anodize under the lug, which leaves a resistive film in the surge path.
- Reading the enclosure bond as the main bonding jumper. The MBJ lands on the neutral bar; the GEC bond does not touch the neutral.
- Bonding one end of a steel raceway run and leaving the other end floating.
- Burying the connection behind finish, where no inspection can reach it.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 12 × 6 in | 304 stainless | 12 x 12 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 12 × 6 in | 316L stainless | 12 x 12 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does the enclosure bond replace the main bonding jumper?
Both stay in place. The main bonding jumper lands the neutral on the enclosure and is sized from the same NEC table as the GEC — the same conductor as the GEC on the worked 200 A service with 4/0 aluminum. The enclosure bond shorts the surge loop around the GEC route. On a switch missing its main bonding jumper, the missing jumper is the violation, and no GEC bond covers it.
Where does the GEC land inside the service switch?
On the grounded neutral terminal or on a ground bar bonded to that terminal, because at the service disconnect the neutral and the enclosure form one system. An isolated ground bar belongs on a subpanel downstream, not in service equipment. Torque the landing to the value marked on the lug and leave the connection accessible for inspection.
What size GEC goes to a ground rod instead of the water pipe?
To a single made electrode such as a ground rod, 6 AWG copper is the largest the NEC requires, so the rod connection can stay 6 AWG even when the water-pipe connection sizes up to the service-sized conductor on a 200 A service. Bond the rod and the water pipe into one electrode system; both serve the same GEC.
Does bonding the GEC to the enclosure put surge current into panel electronics?
The bond equalizes potential: enclosure and conductor rise together, so nothing arcs at the contact point. The lead length that matters is on surge protective devices — keep those leads under about 6 in [150 mm], because a foot of wire is roughly 0.3 µH and at a 20 kA surge rising in 8 µs it drops about 750 V. Keep sensitive boards on a bonded mounting plate.
