Grounding electrode conductor to multiple service disconnects

Short answer: one grounding electrode conductor serves the whole service, and it does not have to enter every disconnect. Bolt a ground bar inside the service wireway, land the conductor from your rods and water pipe on it, and bond that bar to the neutral with a listed compression connector. Size the copper from the NEC grounding electrode conductor table using the largest ungrounded conductor: 4 AWG copper for a 200 A service on 2/0 AWG conductors. If your inspector wants a conductor inside each enclosure, switch to the tap method: one tap per disconnect at the table size, each in its own metal raceway, clears the 6 AWG raceway floor. The NEC lists three connection methods for a service with two or more disconnects, and any one of them meets the rule.

Does a grounding electrode conductor have to land inside every disconnect?

No: with two or more disconnecting means the NEC permits three connection methods, and one of them joins the grounding electrode conductor to the grounded service conductor at a single point on the supply side of the disconnects.

Read the code words as alternatives: the methods are listed with an or, so meeting one of the three meets the rule. Electrically, nothing turns on which one you pick. NEC 250.4(A)(5) keeps the earth out of the effective ground-fault current path, so fault clearing at each disconnect comes from its bonding jumpers, not from the electrode connection. Every disconnect keeps its main bonding jumper between the neutral and its enclosure under all three methods; that jumper is a separate conductor from the grounding electrode conductor. When a request lands for grounding conductors in each enclosure, sort out which conductor the writer means: the bonding jumpers are already there, and the electrode connection is free to land ahead of the disconnects. The grounding and bonding guide covers the conductor types in full.

Which of the three connection methods fits your service?

Use the common-connection method when both disconnects feed from one wireway: the grounding electrode conductors land on a bar bolted inside the wireway, and a jumper of the same size bonds that bar to the neutral, so neither enclosure gains a new opening.

The three methods, in the order you will meet them:

• Taps to each enclosure. A conductor runs from the electrode system to the inside of every disconnecting means enclosure. Pick it when the disconnects sit apart with no shared gutter.
• One common connection point. All electrode conductors end on a single bar; in a gutter install, that is the wireway wall.
• Connection to the grounded service conductor. The electrode connection is made to the neutral on the supply side of the disconnects, which in a wireway is the same bolt as the common bar.

Choose by layout: shared wireway, common bar and neutral bond; disconnects on separate walls, taps in raceway. A written instruction to tap costs you two lengths of copper and ends the conversation. Where the electrode system is a ground ring or building steel rather than rods, the same choice applies and the connection details differ: bonding a disconnect enclosure to the building ground ring walks through that case.

What size does each conductor have to be?

Size every grounding electrode conductor and tap from the NEC grounding electrode conductor table using the largest ungrounded service conductor: on a 200 A service with 2/0 AWG copper that table gives 4 AWG copper, and taps carry floors of 6 AWG in metal raceway and 1 AWG bare.

Worked example, two-family dwelling: 200 A service, two 100 A disconnects, 2/0 AWG copper service conductors.

1. Largest ungrounded conductor: 2/0 AWG copper. The NEC grounding electrode conductor table lists 4 AWG copper for the 2/0 to 3/0 row.
2. Common method: the table-size run from the rods and the water pipe lands on the wireway bar, and a jumper of the same gauge bonds the bar to the neutral through a compression connector.
3. Tap method: two taps at the table size, each in its own metal raceway. The raceway floor is 6 AWG, one gauge size below the tap; the bare floor is 1 AWG, three sizes below it.
4. An 8 AWG tap would sit two gauge sizes under the table value. That is the conductor that comes back with a rejection.

Routing: a 6 AWG or larger copper grounding electrode conductor clear of physical damage may run unprotected; conduit goes on where the copper crosses a zone that can dent or cut it. Keep the electrode conductor separate in your head from the equipment grounding conductor: the EGC rides with each load circuit and takes its size from NEC Table 250.122 against the breaker, 8 AWG copper behind a 100 A breaker and 6 AWG at 200 A.

What do you need before you start?

Gather the copper, the bar and the fittings before the wireway opens: copper at the table size for the common run, a listed irreversible compression connector for the neutral bond, a ground bar on stainless studs, abrasives for the paint, and a torque tool matched to the lugs.

• Copper at the table size, bare or insulated, cut for the runs plus routing slack.
• A ground bar with one terminal per landed conductor plus two spares: four landings in the example call for a six-terminal bar.
• A listed two-port compression connector or tap block for the neutral bond.
• Metal raceway for exposed tap runs; a 3/4 in [19 mm] EMT run takes one tap of that gauge.
• An abrasive pad or flap disc; NEC 250.12 requires paint, lacquer and enamel off the contact surfaces at grounding and bonding connections.
• External-tooth washers for the bar mounting and a torque tool; the value is stamped on each lug.
• A crimp tool with the die matched to conductor and lug together; the selection logic for 6 and 8 AWG copper conductors carries straight over (crimp tool selection for 6 and 8 AWG copper).

A coated box always costs you the scraping step. Bare 304 and 316L stainless ships with no coating to strip, so a bar seats on metal as it comes, and ours are rated NEMA 4X / IP66 by the manufacturer; not UL listed. For a bond-bar compartment away from the service entrance, the custom stainless enclosures page shows the starting sizes and the cutout checklist.

What order do you make the connections in?

Work from the electrodes toward the neutral: land the electrode conductors on the bar, mount the bar on bare metal, bond the bar to the neutral, then add taps, torque every joint, and photograph the work before the covers close.

Open the service only after lockout, and prove the lugs dead with a meter you test on a live circuit first.

1. Lock out and prove dead: shut the service off, set your lock, test the meter on a known live source, then read zero at every lug in the wireway.
2. Mark and strip: scribe the bar footprint inside the wireway and take every coating down to bare metal across the patch and at the stud holes.
3. Mount the bar: stainless studs through the stripped patch, an external-tooth washer under each nut, torqued.
4. Land the electrode conductors: the rod conductors and the water-pipe bond on the bar, with a listed jumper around the water meter.
5. Protect the runs: conduit over any stretch that can be dented, and where a conductor leaves an outdoor enclosure, seal the hole; run a ground wire out of an outdoor enclosure and seal it shows the gland and drip loop.
6. Bond the bar to the neutral: the table-size jumper crimped into the compression connector on the neutral bus, torqued to the stamped value and marked.
7. Run the taps when the tap method applies: one conductor at the table size per disconnect, each in its own metal raceway, landed inside on the neutral terminal or ground bar.
8. Photograph every joint, washer and torque mark, then close the covers.

How do you check the installation when it is done?

Six checks close the job: bare metal under the bar, a torque mark on every lug, tap sizes at or above the table value, a compression joint on the neutral bond, a main bonding jumper in both disconnects, and a photo of each connection.

• Continuity from the neutral bus to a rod: 4 AWG copper runs about 0.25 Ω per 1,000 ft at 20 °C, so the 30 ft path in the example reads under 0.01 Ω; a reading near 1 Ω means paint under a joint or a loose lug.
• A torque mark on every lug and stud, at the value stamped on each.
• Bare metal across the bar footprint and under every washer face.
• Conductor sizes against the table: the common run and both taps at the table size, 8 AWG EGC behind each 100 A breaker.
• The neutral bond made with the irreversible compression connector, and every splice in the electrode path of the compression or exothermic type.
• Photos filed with the job paperwork.

What fails inspection most often?

Four failures cover most rejections: paint left under the ground bar, taps below the table size, a twist-on splice on the neutral bond, and a missing main bonding jumper in one of the two disconnect enclosures.

• Paint under the bar: strip to bare metal, remount with external-tooth washers, and photograph it. The same coating rule hits mounting plates; grounding a mounting plate inside a metal enclosure covers that case.
• A tap below size: an 8 AWG tap on the example service is two gauge sizes under the 4 AWG the table gives; replace it.
• A twist-on splice in the electrode path: run the conductor in one continuous length where you can, and make any needed splice with an irreversible compression connector or an exothermic weld.
• A missing main bonding jumper: install the bonding screw or strap so the neutral bonds to that enclosure; the electrode connection and the jumper are separate jobs.

Get the sizes right, land the connection once, and strip every contact: after that, the method you choose is yours, because all three clear the same rule.

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.

Questions