Short answer: no NEC rule requires that bond, and it would not clear a fault anyway. Your fault path is the equipment grounding conductor run with the feeder. On a 60 A, 480 Y/277 V circuit, that copper loop drives about 1100 A through a ground fault and the breaker clears in a few cycles. The same fault through 25 Ω of earth to the ring carries about 11 A, under 20 % of the rating, so the breaker holds and the frame stays energized. The ring belongs to the service's grounding electrode system, whose work is lightning, surge and voltage stability. Ask the inspector which section applies, treat any bond you end up installing as an auxiliary connection, and keep the EGC either way. The enclosure grounding and bonding guide carries the fundamentals.
The two jobs the inspector is mixing up
A ground ring is a bare copper loop laid around the building, and the NFPA's rundown of the eight items that form the grounding electrode system puts ring and plate electrodes at a minimum depth of 30 in [762 mm]. The ring ties the service to earth, and at this building it is already connected to the service neutral and every other electrode. Its work is lightning, surge and holding the system near earth potential. Soil at that depth is a poor conductor, which is fine for the ring's job and fatal for fault clearing.
Fault clearing is the second job, and it belongs to copper that runs with the circuit. NEC 250.4(A)(5) names the effective ground-fault current path: the conductors back to the source, with the earth left out of it. A jumper from the enclosure to the ring puts the two systems in parallel and changes nothing the breaker needs, because the breaker needs amps the soil will not deliver. Twenty-five ohms of earth against 0.25 Ω of copper tells that story before any test does.
What the NEC asks of a feeder-fed disconnect
A disconnect on the exterior wall, fed from a panel with no transformer between, sits on the load side of the service. For that arrangement the code path is short, and every item on it lands on the enclosure:
- Run the equipment grounding conductor with the feeder, sized from the overcurrent device ahead of it using NEC Table 250.122: 10 AWG copper at 60 A.
- Bond the enclosure into that path. NEC 250.96(A) has every metal part likely to carry a fault bonded so it conducts it, which reaches door bonding straps and continuity on a hinged cover.
- Keep neutral current off the metal. NEC 250.6 aims to keep it off metal parts, so a neutral lands on its own bar and grounds land on the ground bus, the way bonding the ground bus to a panel enclosure shows.
- Hold the bond at every entry. The hub or gland carries the fault path through the wall, which is the point of grounding conductor entry: connector and bond.
- Strip paint and enamel from threads and contact surfaces at bonding points, as NEC 250.12 puts it, and run any insulated EGC of 6 AWG or smaller in green or green with a yellow stripe under NEC 250.119.
A feeder at 150 ft: what trips and what holds
Inputs first. Swap your own numbers in — the method, not the values, is the answer.
| Input | Value | Basis |
|---|---|---|
| System | 480 Y/277 V, three-phase | worked example |
| Overcurrent device ahead | 60 A | worked example |
| Phase conductors | 6 AWG copper, 65 A at 75 °C | NEC copper ampacity at 75 °C |
| EGC | 10 AWG copper | NEC Table 250.122, matched to the device above |
| Route, one way | 150 ft [45.7 m] | worked example |
| Copper resistivity | 1.7 × 10⁻⁸ Ω·m at 20 °C | physics |
| Source impedance | 0.04 Ω | assumption; replace with your available-fault-current data |
| Earth path, ring to pad | 25 Ω | assumption; the NEC's upper bound for one rod electrode, and generous for a soil run |
The rule in words: ground-fault current is the line-to-ground voltage divided by the whole loop, and the breaker trips fast only when the result lands deep in its instantaneous band.
The copper loop:
- EGC resistance (10 AWG, 5.26 mm²): R = ρL / A = (1.7 × 10⁻⁸ Ω·m × 45.7 m) ÷ (5.26 × 10⁻⁶ m²) = 0.15 Ω.
- Phase resistance, same 45.7 m at 13.3 mm²: (1.7 × 10⁻⁸ × 45.7) ÷ (13.3 × 10⁻⁶) = 0.06 Ω.
- Loop with the source: 0.15 + 0.06 + 0.04 = 0.25 Ω.
- Fault current: 277 V ÷ 0.25 Ω = 1108 A, about 18× rating. That is deep in the instantaneous band of a thermal-magnetic breaker, and clearing takes a few cycles — one cycle at 60 Hz is 16.7 ms.
- Hot check: copper rises about 0.39 % per K, so a 75 °C conductor loop of 0.21 Ω grows to 0.26 Ω and still delivers about 920 A, 15× rating.
The earth path:
- 277 V ÷ 25 Ω = 11 A, which is 18 % of the rating.
- Eleven amps sits below the breaker's continuous rating, so the fault stays on the frame as long as the supply holds.
| Path | Loop | Current at 277 V | Breaker |
|---|---|---|---|
| 10 AWG EGC + 6 AWG phase, 150 ft | 0.25 Ω with source | ≈1108 A, 18× rating | instantaneous trip, cleared in cycles |
| Ring through 25 Ω of soil | 25 Ω | ≈11 A, 18 % of rating | holds; fault stays on the frame |
The threshold that decides it: a path earns its keep only if it pushes the fault into the breaker's instantaneous band. The EGC clears at 18× rating; the ring sits at 18 % and stays there. One safety note, because this is the real hazard: a fault the breaker never sees leaves the frame near 277 V, and 277 V through a 1 kΩ wet hand-to-hand path drives about 280 mA — nearly ten times the 30 mA RCD protection level and far past the 10-16 mA let-go range.
What the ring bond actually is
Treat the bond the inspector wants as an auxiliary electrode. NEC 250.54, as our grounding guide states it, allows an electrode driven beside an enclosure to be connected to the equipment grounding conductor, and calls it never a substitute for that conductor. A jumper from the disconnect to the ring sits in the same category: permitted, harmless to fault clearing while the EGC stays in place, and worth something only for static and lightning.
The NEC also keeps the two conductors on two separate jobs. The grounding electrode conductor ties the service, or a separately derived system, to earth; the EGC returns fault current to its source. Running a feeder's EGC out to an electrode blurs that line, which is the mix-up behind the request. Call the jumper an auxiliary bond, keep it short and direct, and the question of it serving as an electrode conductor goes away.
Answering the inspector
Take the numbers to the conversation in this order:
- Show the EGC running with the feeder, sized against Table 250.122: 10 AWG copper.
- Quote NEC 250.4(A)(5): the effective ground-fault current path is the conductor path, and the earth is not part of it. The 1108 A against 11 A comparison is the whole argument in one line.
- Ask which section the ruling rests on. For a feeder-fed disconnect on a load-side wall there is none, and the building's electrodes are already tied together at the service.
- If the ruling stands, install the bond well: at least 6 AWG copper to the ring, a clamp listed for direct burial on the ring conductor, and mechanical protection wherever the run could be struck. The NEC lets a 6 AWG or larger copper electrode conductor run along a surface without raceway only where it is not exposed to physical damage.
- Keep the EGC regardless, and note the auxiliary bond on the as-built so the next person reads a permitted addition, not a change of fault path.
When the ring does matter
Grounding electrode conductors earn their keep in two places: service equipment and separately derived systems. A transformer or a generator on site changes the answer, because there an electrode conductor lands on the electrode system — the family of connections shown in bonding a panelboard ground bar to building steel. A wall disconnect fed from a panel is neither of those. It is load-side gear with the service and its electrodes behind it, so it takes an EGC and nothing else. The air handler on the pad follows the same rule: the EGC continues with the load conductors out of the disconnect and lands on the unit's grounding terminal.
What to order for that wall
If the disconnect enclosure is on your scope, spec it for the wall it hangs on. Type 3R handles rain, sleet and snow on an exterior wall; Type 4X stainless fits walls that see hose-down or salt spray — 304 for most sites, 316L within sight of the ocean — and the 3R versus 4X guide splits the cases. Put the feeder entry in the order as a cutout for a bonding-type hub, or as glands when the run to the pad is cable, since gland earthing carries the fault path through the entry. You set the width, height, depth and every cutout in custom enclosures, and the box is delivered in 10 business days counted from your approval of the drawing. The NEMA type on our boxes is a manufacturer rating for the specified design; the enclosures are not UL listed.
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
Does the NEC require a bonding jumper from a disconnect enclosure to a ground ring?
No. For a disconnect fed from a panel, the NEC requires the equipment grounding conductor run with the feeder, sized from the overcurrent device ahead of it using NEC Table 250.122 — 10 AWG copper at 60 A. The ground ring belongs to the service's grounding electrode system. Ask which section the inspector is applying; for load-side gear there is none.
Can the ground ring clear a ground fault instead of the EGC?
No. At 480 Y/277 V, a 25 Ω earth path — already generous for a rod-to-rod run — carries about 11 A, under 20 % of the breaker's rating, so it never trips. The 10 AWG copper EGC on the same circuit delivers about 1108 A and clears in a few cycles. Under NEC 250.4(A)(5) the earth is not part of the effective ground-fault current path.
Is there harm in installing the ring bond if the inspector insists?
Not to the fault path, provided the EGC stays. The NEC treats an electrode beside an enclosure as an auxiliary electrode under 250.54: it may connect to the EGC, and it is never a substitute. Use at least 6 AWG copper, a clamp listed for direct burial on the ring, and mechanical protection anywhere the run is exposed to damage.
Where does a grounding electrode conductor actually apply?
At service equipment and separately derived systems — a transformer, a generator. There a grounding electrode conductor ties the system to the electrode system, and the ring is one of those electrodes, buried at least 30 in [762 mm]. A wall disconnect fed from a panel is load-side gear: it takes an EGC, and the ring question never comes up.
Should the air handler on the pad also get a ground rod?
Not as its fault path. The EGC continues with the load conductors from the disconnect to the unit, and any electrode at the pad is auxiliary under the same NEC rule: permitted to connect, never a substitute. Land the conductor on the unit's grounding terminal and the fault path is complete.
