Sizing the grounding electrode conductor for the Texas exam, and the three ceilings that cut the answer short

What the exam does with it

Seventeen of the 66 grounding and bonding items in our 500 question bank name the grounding electrode conductor, and four cite 250.66 directly. That's a smaller share than the equipment grounding conductor takes, and the items run harder, because almost every one is built on a step people skip.

They arrive in three forms. One describes a service and an electrode and asks for a size, and the wrong answers are the raw table value. One describes an installation detail, a splice, a steel sleeve or a landing point, and asks whether it's allowed. One puts this conductor and the equipment grounding conductor in the same stem and asks you to tell them apart, with a wrong answer that sizes both from one table.

All three reward the same preparation, which is knowing 250.66 is a two-step rule. Read the table, then read the subsection matching the electrode at the far end. A candidate who stops after step one gets a conductor two or three trade sizes too large, and that answer's sitting on the sheet waiting.

Where this conductor lands

Article 100 describes it as a conductor used to connect the system grounded conductor, or the equipment, to a grounding electrode or to a point on the grounding electrode system. In plain terms it's the wire from the service out to the earth, and its far end is the tell that identifies it on an item.

At a service the connection is made at any accessible point from the load end of the service conductors to the terminal or bus where the grounded service conductor lands at the service disconnecting means (NEC 250.24(A)(1)). That's a range of acceptable points, and items exploit it by describing a landing spot and asking whether it falls inside.

One permission gets missed often enough to be worth a line. Where the main bonding jumper is a wire or busbar running from the grounded conductor bar to the equipment grounding bar, this conductor may land on the equipment grounding terminal (NEC 250.24(A)(4)). Which conductors qualify as a main bonding jumper, and how each sizes, sits on the bonding jumpers page.

Accessibility carries its own rule at 250.68(A), and its exception is what makes footing electrodes usable, because a connection buried or encased in concrete is excused from being accessible.

The table starts the answer

Size comes from Table 250.66, entered with the largest ungrounded conductor supplying the service. For a separately derived system it's the largest ungrounded derived conductor, and parallel sets go in on their combined equivalent area.

Find the size and read across to the value. On an item with a metal water pipe electrode and nothing else, that's the whole method.

The sentence that sends you to the table also excepts what follows it, and the three subsections behind it are where the other items live. Each names a maximum above which a larger conductor is uncalled for, and which one applies turns on the kind of electrode at the far end.

The three ceilings by electrode

Each subsection attaches to an electrode type and states a maximum.

• To a rod, pipe or plate electrode, single or multiple, the conductor is capped at 6 AWG copper, or 4 AWG aluminum or copper-clad (NEC 250.66(A)).
• To a concrete-encased electrode, the one the trade calls a Ufer, the cap is 4 AWG copper (NEC 250.66(B)).
• To a ground ring, the cap is the size of the conductor used for the ring itself (NEC 250.66(C)).

Two of the bank's items are built on mixing up the first two figures. A stem with a driven rod at the far end and a table value of 2 AWG will offer 6 AWG copper as the answer and 4 AWG copper as the near miss, and the trap note on that near miss says the candidate reached for the concrete-encased ceiling.

Notice what the ceilings leave alone. A metal underground water pipe electrode has no subsection and no cap, so the table governs the whole run to it. That's worth a margin note in your own book, because an item with a large service and a water pipe electrode is testing whether you go looking for a ceiling nobody wrote.

The condition attached to all three

All three subsections carry the same qualifier, and it's the half that gets skipped: the ceiling holds only where that conductor stops at that electrode and goes no further to a type calling for a larger conductor.

Four cases at one 400 ampere service settle it.

• Two driven rods and nothing else. The conductor stops there, so 250.66(A) caps it at 6 AWG copper whatever the table says for the service conductors.
• A metal underground water pipe and two rods, with one conductor running to the pipe and continuing on to the rods. It serves a water pipe, which has no ceiling, so the table value governs the whole run.
• The same building where a separate jumper reaches the rods and the main conductor goes only to the pipe. The jumper is capped at 6 AWG and the conductor to the pipe is at the table value, so one building gives you two conductors with two different answers.
• A footing electrode alone, capped at 4 AWG copper by 250.66(B). Add a ground ring later and the conductor reaching both sizes on whichever electrode calls for more.

The tell in an item is a second electrode type in the stem. Read it for whether one conductor reaches both, because that's the fact switching the ceiling off. The bank's trap note on the standard error puts it exactly: the candidate took the smallest ceiling for the whole run, when each one attaches to a conductor serving that electrode alone.

One continuous length and its exceptions

The conductor goes in as one continuous length, free of splice or joint, subject to four carve-outs that 250.64(C) names by section number: 250.30(A)(5), 250.30(A)(6), 250.30(B)(1) and 250.68(C).

Inside that, a short list of connections is permitted and behaves like an exception list of its own. Irreversible compression connectors listed for grounding and bonding qualify, so does exothermic welding, and so do busbar sections bolted together. The bolted, riveted or welded connections in a structural metal frame count, as do threaded, welded, brazed, soldered and bolted-flange connections in metal water piping.

A wire nut sits outside that list, and so does a split bolt. That single fact is the whole item most of the time, and the answer choices will offer a tidy field method that falls outside what the section permits.

Connection methods at the electrode end are set separately at 250.70, which is a different question from whether the run may be spliced. Keep the two apart before test day, because an item can ask about either one in similar words.

Protection, sleeves and aluminum

Three installation rules produce most of the remaining items, and each hinges on a single fact in the stem.

Physical protection turns on wire size. At 6 AWG and larger it depends on exposure to physical damage, and a conductor free of that exposure may run along the surface of the building without a metal covering (NEC 250.64(B)(1)). Below 6 AWG that test disappears and protection in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC, RTRC-XW, electrical metallic tubing or cable armor is required either way. So the hinge is the size, and an item describing a small conductor in a sheltered spot is built on candidates sorting it by location.

A ferrous metal raceway, enclosure or cable armor around the conductor is bonded at each end, which puts the steel electrically in parallel with the conductor inside it (NEC 250.64(E)). Left unbonded the steel acts as a choke, because the changing field induces an opposing current in it and the impedance climbs.

Aluminum carries two 18 inch rules measured from different surfaces (NEC 250.64(A)). One permits a termination within 18 inches of the bottom of an outdoor enclosure listed and identified for the environment. The other keeps a termination 18 inches clear of the earth. Same figure, opposite direction, and an item can quote either one.

Telling this conductor from the other

Ask what the conductor terminates on. An electrode, or a point on the electrode system, means this conductor and Table 250.66. Anything running alongside the circuit conductors and landing on equipment is the equipment grounding conductor, sized from a different table on a different input entirely.

The code settles the question of whether one wire can do both jobs. 250.121 keeps an equipment grounding conductor from being used as a grounding electrode conductor, with a narrow allowance for a single wire-type conductor installed so that it satisfies both sets of requirements. That allowance sits a long way from relabeling a conductor already doing one of the jobs, and the bank has an item built on somebody doing exactly that at a panel.

The far-end test also sorts the jumpers. 250.66 sizes the bonding jumpers that connect electrodes to each other, so a conductor with bonding in its name can still belong to the earth side. The reasoning behind the whole split is worked through on grounding compared with bonding, worth reading first if the two terms still feel interchangeable.

What to do before test day

Four moves with your own book, all finished beforehand.

1. Tab Table 250.66 and write the three ceilings in the margin beside it: 6 AWG copper to a rod, pipe or plate, 4 AWG copper to a concrete-encased electrode, and the ring conductor size to a ground ring. Add the qualifier about continuing to another electrode type.
2. Tab Table 250.122 as well, several pages away, so the two sizing tables never get confused. Texas allows only publisher-made tabs, so buy a printed set.
3. Write the two-step order at the top of the table: read the table, then apply the subsection matching the electrode. Notes written in beforehand are allowed and marking the book during the session is barred, so it's done at home.
4. Work ten items where you name the electrode at the far end before you look at any answer choice. That habit is what converts a two step rule into a reflex inside 2.2 minutes.

From September 1, 2026 Texas exams reference the 2026 edition under 16 TAC 73.100, which our page on which code edition applies covers. For the code reading and the worked sizing arithmetic on this conductor, the question sets has the grounding electrode conductor. Then sit the timed set of thirty free questions.

Questions people ask

What size grounding electrode conductor goes to a ground rod?

Start at Table 250.66, entered with the largest ungrounded conductor supplying the service, and then apply NEC 250.66(A), which caps a conductor running to a rod, pipe or plate electrode at 6 AWG copper or 4 AWG aluminum. The cap holds only where that conductor serves the rod alone and goes no further to an electrode type calling for more. On a 400 ampere service with two driven rods and nothing else, the answer is 6 AWG copper however large a figure the table hands you. The raw table value will be sitting there as an answer choice.

Is the grounding electrode conductor allowed to be spliced?

NEC 250.64(C) installs it in one continuous length free of splice or joint, subject to four carve-outs it names by section number. Inside that, a short list of connections is permitted: irreversible compression connectors listed for grounding and bonding, the exothermic welding process, busbar sections bolted together, the bolted, riveted or welded connections in a structural metal frame, and threaded, welded, brazed, soldered or bolted-flange connections in metal water piping. A wire nut falls outside that list and so does a split bolt, which is the whole of most exam items on this rule.

What is the difference between the GEC and the EGC?

The far end tells you. The grounding electrode conductor ends on an electrode or on a point on the grounding electrode system, and it sizes from Table 250.66 entered on the service conductor size, with three ceilings that can cut the answer short. The equipment grounding conductor runs with the circuit conductors, lands on equipment, and sizes from Table 250.122 entered on the rating of the overcurrent device ahead of the circuit. NEC 250.121 also keeps one conductor from being relabeled as the other, with a narrow allowance for a wire that satisfies both sets of requirements.

Does a steel sleeve around the conductor need to be bonded?

Yes, where the raceway, enclosure or cable armor is ferrous. NEC 250.64(E) bonds it at each end to the conductor or to the electrode, which puts the steel electrically in parallel with the conductor running inside it. Unbonded steel behaves as a choke, because the changing magnetic field induces an opposing current in it and the impedance of the path climbs, which is the opposite of what the sleeve was installed to achieve. The bonding jumper is the same size as or larger than the largest grounding electrode conductor inside. Nonferrous raceway is free of this requirement.

Where can the grounding electrode conductor connect at a service?

At any accessible point from the load end of the service conductors to the terminal or bus where the grounded service conductor lands at the service disconnecting means, under NEC 250.24(A)(1). That is a range, and items describe a landing spot and ask whether it falls inside it. NEC 250.24(A)(4) adds a permission worth knowing: where the main bonding jumper is a wire or busbar running from the grounded conductor bar to the equipment grounding bar, this conductor may land on the equipment grounding terminal. Connections that are buried or encased in concrete are excused from the accessibility rule at 250.68(A).

When does the physical protection requirement apply?

Conductor size decides it. At 6 AWG and larger, protection turns on whether the conductor is exposed to physical damage, and a conductor free of that exposure may run along the surface of the building without a metal covering under NEC 250.64(B)(1). Below 6 AWG that test goes away, and protection in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC, RTRC-XW, electrical metallic tubing or cable armor is required wherever it runs. An item that describes a small conductor in a sheltered location is checking whether you sort this on size or on where the wire happens to be.