Connect the grounding electrode conductor once, on the neutral at the service disconnect, and let the raceway bond everything after it. For a 400 A service feeding four 100 A meter sockets, that is one GEC connection at the main disconnect. No conductor chases the trough, the meter pans or the breaker enclosures. Steel EMT is on the NEC's list of raceways allowed as an equipment grounding conductor, so the metal path does the bonding. A separate jumper shows up only at a concentric knockout on a circuit over 250 V to ground. Here is the rule, the arithmetic and the drawing notes; the grounding and bonding guide carries the fundamentals behind it.
One connection, at the service disconnect
The NEC requires the grounding electrode conductor to land on the grounded conductor at the service disconnecting means — the same terminal group where the main bonding jumper ties the neutral to the enclosure. From there the GEC runs out to the grounding electrode system and stops. One connection covers the whole service.
Everything on the load side of that disconnect behaves like a subpanel, and the guide to sizing an electrical enclosure covers how feeders, bending space and fill work inside those cabinets. In cold-sequence metering the 400 A disconnect sits ahead of the meter bank, so the trough, the four meter sockets and their breaker enclosures are all load side. Each neutral lands on an isolated bar and never touches its can; each can bonds to the raceway. NEC 250.6 draws that line on purpose: it aims to keep neutral current off metal parts, so neutrals sit on isolated terminals while grounds ride the bonding path. A second neutral-to-ground bond anywhere downstream would push load current through the enclosures.
What bonds the meter pans, trough and breaker cans
The raceway bonds them — not a wire you add afterward. Steel EMT and rigid metal conduit sit on the NEC's list of raceways allowed as equipment grounding conductors. The EMT sleeve from trough to breaker enclosure is then that enclosure's fault path, and the grounding and bonding guide covers when a raceway counts as the equipment grounding conductor. NEC 250.96(A) requires metal parts serving as grounding conductors — raceways, fittings, enclosures — to be bonded so they carry the fault current likely to hit them.
The joints make or break the path. Use listed steel fittings pulled tight and standard locknuts seated hard on bare metal. Remove paint or powder coat from threads and contact surfaces, which NEC 250.12 requires at grounding and bonding connections. A 5-jaw socket in a cold-sequence bank fits the same picture: the fifth terminal passes the grounded conductor through the meter to the tenant feeder, while the socket shell bonds through its raceway connection. At the wall of the enclosure the entry hardware matters too — the cutouts, glands and HMI windows guide sorts out the connector and the bond there.
When a concentric knockout needs a jumper
The NEC draws the line at 250 V to ground. A 120/240 V service sits at 120 V to ground, and a 208Y/120 V system sits at 120 V to ground too. On either, a concentric or eccentric knockout needs no bonding jumper: leave the ring intact and pull the fitting tight. On a 480Y/277 V system the enclosure sits at 277 V to ground, over the line. Each concentric knockout then needs a bonding jumper with a bushing, or equipment the manufacturer lists and marks for grounding without one.
Size the jumper from NEC Table 250.122, which keys the conductor to the overcurrent device ahead of the run: 8 AWG copper for a 100 A device, 3 AWG copper at 400 A. The aluminum column reads 6 AWG and 1 AWG for the same two ratings.
Worked example: the earth against the raceway
Take the 400 A service at 120/240 V with a hot-to-can fault at a breaker enclosure. First suppose the enclosure leaned on the earth: a ground rod at the meter bank and no metal path back. Give the soil a good reading of 10 Ω, the value grounding handbooks call a solid driven-rod result. The fault current is 240 V ÷ 10 Ω = 24 A. The magnetic element of a thermal-magnetic 100 A breaker trips at roughly 5 to 10 times its rating, the band molded-case makers build in, so 500 to 1,000 A. The earth delivers 24 A — 2 to 5 percent of that band — and the fault cooks the enclosure instead of clearing.
Now bond the same can back through steel EMT. A 40 ft run of 2½ in EMT adds a few hundredths of an ohm of steel wall. Even with a generous allowance for fittings and reactance, the path stays under 0.1 Ω. The fault current is at least 240 V ÷ 0.1 Ω = 2,400 A, well past the top of the trip band, and the magnetic trip clears in a fraction of a second.
That gap is why NEC 250.4(A)(5) treats the earth as outside the effective ground-fault current path: fault current returns over metal, and the raceway is that metal. An auxiliary rod under NEC 250.54 may ride along, connected to the equipment grounding conductor, but it never replaces the metal path.
What goes on the drawing
List these five items and the inspector reads the design straight off the sheet:
- One grounding electrode conductor, landed on the neutral at the 400 A service disconnect, run from there to the electrode system.
- Metallic raceway — steel EMT or rigid — over every load-side run, with listed fittings pulled tight and contact surfaces on bare metal.
- Neutral bars isolated in the trough, all four meter sockets and all four breaker enclosures; grounds land on the bonding path only.
- Concentric knockouts: ring intact and jumper-free at 120 V to ground; on a 480Y/277 V panel at 277 V to ground, a Table 250.122 jumper (8 AWG copper on the socket feeders) or equipment marked for grounding without one.
- Any ground rod at the meter bank marked as an auxiliary electrode under NEC 250.54, tied to the equipment grounding conductor.
The same sheet drives the box itself. When the metering section needs a stainless enclosure, cutouts drawn on custom stainless enclosures come cut to your drawing, and a plain machine-cut opening keeps every entry jumper-free. Where the panel carries listed control equipment, the UL 50E and NEMA 250 listing guide explains what the inspector expects on the marking.
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 |
| 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
Does every meter pan need its own grounding electrode conductor?
No. The NEC requires the grounding electrode conductor to connect to the grounded conductor at the service disconnecting means, one time. For a 400 A service with four meter sockets, that is one connection at the 400 A disconnect. Each socket, trough and breaker enclosure downstream bonds through the metallic raceway with tight fittings. A wire-type equipment grounding conductor is added only where the raceway is interrupted, for example by a nonmetallic section.
Is EMT alone enough as the equipment grounding conductor?
Yes, on the load side of the service disconnect. The NEC lists steel EMT among the raceways allowed as an equipment grounding conductor, so a bonded 40 ft run back to the disconnect keeps fault current in the thousands of amperes — well above the 500 to 1,000 A magnetic trip band of the socket breaker. Use listed steel fittings, pull them tight, and remove paint from contact surfaces as NEC 250.12 requires.
Does a 5-jaw cold-sequence meter socket change the GEC routing?
No. In cold-sequence metering the meter sits on the load side of the disconnect, so each 5-jaw socket is ordinary load-side equipment bonding through its raceway. The fifth terminal passes the grounded conductor through the meter to the tenant feeder. Four sockets mean four pass-through terminals and still one GEC connection at the main disconnect. Treat each breaker enclosure after the meter like a subpanel: neutral on the isolated bar, can bonded through the raceway.
Can a ground rod at the meter bank do the grounding instead?
It rides along, it never takes over. NEC 250.54 lets an auxiliary electrode connect to the equipment grounding conductor, but the fault path still has to be metal. Give the earth every advantage at 10 Ω: a 240 V fault through it delivers 24 A, a fraction of the 500 to 1,000 A needed for an instant magnetic trip. The raceway clears the fault; the rod touches the earth.
What size bonding jumper fits a concentric knockout over 250 V to ground?
Pick it from NEC Table 250.122: 8 AWG copper on a socket feeder, 3 AWG copper on the 400 A main (6 AWG and 1 AWG aluminum for the same two ratings). The jumper applies on a 480Y/277 V system, where 277 V to ground sits over the NEC's 250 V line; a 120/240 V service sits at 120 V to ground and needs no jumper at a concentric knockout.
