3.5 Grounding Electrode Conductor Installation & Connections (0202)
Key Takeaways
- 250.64(A) permits bare, covered, or insulated aluminum grounding electrode conductors only where not in contact with masonry or earth, and prohibits them within 18 in. of the earth.
- 250.64(B) requires a grounding electrode conductor 6 AWG or larger to be protected where exposed to physical damage, and a 6 AWG copper conductor may be run along a building surface without protection where free from damage; smaller than 6 AWG must be in a raceway or armor.
- 250.64(C) requires the grounding electrode conductor to be installed in one continuous length without a splice, except by irreversible compression connectors listed for the purpose, exothermic welding, busbar sections, or bolted busbar connections.
- 250.64(E) requires ferrous metal enclosures and raceways for grounding electrode conductors to be electrically continuous and bonded at both ends, so the raceway does not act as a choke on fault current.
- 250.68(A) requires the connection to the electrode to be accessible, except that an encased or buried connection — such as at a concrete-encased electrode or a driven rod below grade — is permitted to be inaccessible.
Sizing Is the Easy Half
Section 3.2 covered Table 250.66 and the three caps that modify it. On the job, the grounding electrode conductor (GEC) is far more often written up for how it was installed than for what size it is. This section is the installation half of sub-topic 0202.
Material and Where Aluminum May Not Go — 250.64(A)
A GEC may be copper, aluminum, copper-clad aluminum, or stainless steel, and may be solid or stranded, bare, covered, or insulated. But aluminum and copper-clad aluminum carry two restrictions:
- They shall not be used where in direct contact with masonry or the earth, or where subject to corrosive conditions.
- Where used outdoors, they shall not be terminated within 18 in. (450 mm) of the earth.
That second rule is the one field inspectors use: an aluminum GEC clamped to a ground rod at grade is a violation on its face, because the termination sits at the earth. Bare aluminum GECs installed in a concrete slab or run along a masonry foundation wall fail the first rule.
Physical Protection — 250.64(B)
The protection requirement is written by conductor size, and the thresholds are worth memorizing:
| GEC size | Protection required |
|---|---|
| 4 AWG and larger | Protected if exposed to physical damage; a 4 AWG or larger conductor may be run along the surface of the building without metal covering where not exposed to physical damage |
| 6 AWG | May be run along the surface of the building without metal covering or protection where free from exposure to physical damage and securely fastened; otherwise, in RMC, IMC, PVC, RTRC, EMT, or cable armor |
| Smaller than 6 AWG | Shall be in RMC, IMC, PVC, RTRC, EMT, or cable armor — no exposed run is permitted |
The practical takeaway: a 6 AWG copper GEC stapled up a basement wall to a driven rod is acceptable; a 8 AWG doing the same thing is not.
Continuous Without a Splice — 250.64(C)
The GEC must be installed in one continuous length without a splice or joint. Four things are permitted anyway:
- Irreversible compression-type connectors listed as grounding and bonding equipment, or exothermic welding.
- Sections of busbar connected together.
- Bolted, riveted, or welded connections of structural metal frames of buildings.
- Where a service consists of more than one enclosure as permitted by 230.71, the GEC may be run to a busbar and tapped to each enclosure — the busbar must be not smaller than 1/4 in. × 2 in., securely fastened, installed where accessible, and each tap connection must be made by a listed connector or by exothermic welding.
A wire nut, a split-bolt, or a mechanical lug in the middle of a GEC run is not on that list. That is a very common write-up.
The Ferrous Raceway Trap — 250.64(E)
Where a GEC is installed in a ferrous metal raceway, enclosure, or cable armor, that metal enclosure must be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode, and must be securely fastened to the ground clamp or fitting. Any ferrous raceway that is not physically continuous must be made continuous by bonding each end to the grounding electrode conductor.
The physics is worth understanding rather than memorizing. A steel conduit surrounding a single current-carrying conductor acts as a magnetic choke: the alternating flux from the GEC current induces opposing currents in the steel and dramatically raises the impedance of the path. Bonding both ends of the raceway to the GEC puts the steel in parallel with the conductor instead of in series with the flux, and the choking effect disappears. A GEC pulled through a steel sleeve that is bonded at neither end can have several times its expected impedance — the conductor is the right size and the installation still does not work.
Where the raceway is nonferrous — PVC or aluminum — the bonding requirement does not apply, which is why PVC is the common choice for a GEC sleeve.
Connections to the Electrode — 250.68 and 250.70
- 250.68(A) Accessibility. The connection of a grounding electrode conductor or bonding jumper to a grounding electrode must be accessible. Two exceptions: an encased or buried connection to a concrete-encased, driven, or buried electrode need not be accessible, and exothermic or irreversible compression connections to fireproofed structural metal need not be accessible.
- 250.68(B) Effective grounding path. The connection must be made in a manner that the installation of equipment — such as a water meter or a filter — will not likely be disconnected during normal use, which is why a bonding jumper around the water meter is required.
- 250.68(C)(1) Interior metal water pipe. Interior metal water piping located not more than 5 ft (1.52 m) from the point of entrance to the building may be used as a conductor to interconnect electrodes. In industrial, commercial, and institutional buildings where conditions of maintenance and supervision ensure qualified persons service the installation, the entire length of interior metal water pipe may be used if it is exposed.
- 250.70 Methods of connection. The connection must be by listed lugs, pressure connectors, clamps, or other listed means, and the fitting must be listed for the materials of the electrode and the conductor. Not more than one conductor may terminate on a single clamp unless the clamp is listed for multiple conductors. Solder shall not be used. A ground clamp used on a buried or direct-contact electrode must be listed for direct soil burial or concrete encasement.
Three-item field check. Walk the GEC from the service to the electrode and ask: is it continuous, is it protected for its size, and is every ferrous sleeve bonded at both ends? Those three questions catch the overwhelming majority of GEC defects.
A 6 AWG copper grounding electrode conductor is run exposed along the surface of a basement wall to a driven ground rod, securely stapled and not subject to physical damage. Is this acceptable?
A grounding electrode conductor is pulled through a steel sleeve that passes through a foundation wall. The sleeve is bonded at neither end. What is wrong?
Which of the following is a permitted way to join two sections of a grounding electrode conductor under 250.64(C)?