Written against the 2026 NEC and checked section by section, September 2026
Grounding Electrode Conductor Practice Questions
Sizing straight off Table 250.66 gives the wrong answer on any rod only or footing only system, because three short subsections cap the result depending on what sits at the far end of the conductor. These 25 items work the table, the three ceilings and the condition attached to all of them, then move on to the installation rules in 250.64 where the continuous length requirement, the 6 AWG protection hinge and the ferrous raceway jumper live. Every conductor size comes out of the table as the 2026 edition prints it.
Pick an answer and the explanation opens with the section it comes from. These are original questions written for this site, not questions from the exam. Have your own code book open: the Texas exam is open book, and looking the section up is the skill being tested.
Read the grounding electrode conductor study page first if the topic is new to you.
1. Article 100 defines the grounding electrode conductor as a conductor used to connect what?
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B. The system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system
The definition names the far end as an electrode or a point on the electrode system, and that is the fastest way to tell this conductor from the equipment grounding conductor. A conductor tying electrodes to each other is a bonding jumper. The connection between the neutral bar and the equipment ground bar is the main bonding jumper, a third thing again.
NEC 2026 Article 100, 250.66
2. Table 250.66 is entered with which quantity?
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A. The size of the largest ungrounded service or derived conductor
The left column of the table is the size of the largest ungrounded conductor supplying the service, or for a separately derived system the largest ungrounded derived conductor. The device rating belongs to the other grounding table entirely. Parallel sets go in on their combined equivalent area rather than on one conductor.
NEC 2026 250.66, Table 250.66
3. A service is wired in 4/0 copper and the electrode is a metal underground water pipe. What size copper grounding electrode conductor does the table call for?
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C. 2 AWG
Four aught copper falls in the row running over 3/0 through 350 kcmil, and that row gives 2 AWG copper. A water pipe electrode carries no ceiling, so the table value stands as the answer. The rod and footing ceilings that would cut this figure do not reach this installation.
NEC 2026 Table 250.66, 250.66
4. A service runs two parallel sets of 350 kcmil copper per phase. Assuming the electrode places no ceiling on it, what size copper grounding electrode conductor does the table call for?
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D. 2/0 AWG
Parallel sets enter the table on their combined equivalent area, so two 350 kcmil conductors count as 700 kcmil. That lands in the row running over 600 through 1100 kcmil, which gives 2/0 copper. Reading the table at one 350 kcmil conductor gives 2 AWG, several sizes light, and that answer is on the sheet for anyone who forgets to add.
NEC 2026 Table 250.66, 250.66
5. A service is wired in 500 kcmil aluminum. What size copper grounding electrode conductor does the table call for?
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A. 2 AWG
The table carries separate columns for the material of the service conductor, and 500 kcmil aluminum sits in the row running over 250 through 500 kcmil. That row gives 2 AWG copper or 1/0 aluminum for the electrode conductor. Reading the copper service column while holding an aluminum service conductor size pulls the answer a row off.
NEC 2026 Table 250.66
6. A service is wired in 1100 kcmil copper and the only electrode at the building is two driven rods. What size copper grounding electrode conductor is required?
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B. 6 AWG
The table gives 2/0 copper for that conductor size, and then the rod, pipe and plate ceiling holds the answer at 6 AWG copper because the conductor stops at the rods. The table figure is sitting on the sheet for anyone who reads across and quits. Answering with the table value on a rod only service is the most common miss in this topic.
NEC 2026 Table 250.66, 250.66(A)
7. What switches the rod, pipe and plate ceiling off?
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D. The same conductor continuing on to another type of electrode that requires a larger conductor
All three ceilings carry the same qualifier and it is the half people skip. A ceiling holds only while that conductor does not extend on to an electrode type calling for more. Two rods rather than one changes nothing, and neither does the size of the service or the conductor material.
NEC 2026 250.66(A), 250.66(B), 250.66(C)
8. At one building a conductor runs from the service to a metal underground water pipe, and a separate bonding jumper reaches two driven rods from the electrode system. How are the two sized?
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C. The conductor to the pipe at the table value, and the jumper to the rods capped at 6 AWG copper
The rod ceiling is written about the conductor or jumper connected to the rods, so it caps that jumper and nothing else. The conductor going to the water pipe reaches an electrode with no ceiling on it and takes the table value. One building can carry two different answers, and what decides each is which electrode that particular conductor lands on.
NEC 2026 250.66(A), Table 250.66
9. A building has a concrete encased electrode and nothing else, and the service conductor size puts the table value at 1/0 copper. What size copper grounding electrode conductor is required?
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A. 4 AWG
The concrete encased ceiling stops the conductor at 4 AWG copper as long as it does not carry on to another electrode type calling for more. So the table figure of 1/0 gets cut to 4 AWG. That number is different from the rod ceiling, and the two get swapped constantly.
NEC 2026 250.66(B), Table 250.66
10. What limits the size of the conductor running to a ground ring?
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D. The size of the conductor used for the ring itself
The ground ring ceiling is the only one of the three that is not a fixed size. It points at the ring conductor, so a ring built from 2 AWG bare copper caps the conductor reaching it at 2 AWG. The two fixed numbers belong to the rod ceiling and to the footing ceiling.
NEC 2026 250.66(C)
Ten down. If you want these timed and scored by content area, the practice exam runs thirty questions free, and the full bank of 178 plus the calculation ladder is $79 once.
11. At a service, where may the grounding electrode conductor connection be made?
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B. 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
The section describes a range rather than one point, running from the load end of the overhead service conductors, service drop, underground service conductors or service lateral to the grounded conductor terminal at the disconnect. Items exploit that range by naming a landing spot and asking whether it falls inside it. A meter enclosure sits on the line side of the range.
NEC 2026 250.24(A)
12. The main bonding jumper in a service is a wire running from the grounded conductor bar to the equipment grounding bar. What does that permit?
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C. The grounding electrode conductor may be connected to the equipment grounding terminal, bar or bus that the main bonding jumper lands on
A short subsection says that where the main bonding jumper is a wire or busbar run between the two bars, the electrode conductor may land on the equipment grounding side instead. It is tied to the form of the main bonding jumper, so a screw type jumper does not trigger it. Nothing about the continuity rule changes.
NEC 2026 250.24(A)(4), 250.28
13. The grounding electrode conductor is installed in one continuous length without a splice or joint. Which connection is permitted anyway?
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A. An irreversible compression connector listed as grounding and bonding equipment
The permitted list is short: irreversible compression connectors listed for grounding and bonding, the exothermic welding process, splices at accessible locations made with listed grounding and bonding equipment, busbar sections bolted together, bolted, riveted or welded connections of structural metal frames, and threaded, welded, brazed, soldered or bolted flange connections in metal water piping. A wire nut and a split bolt are not on it. That single fact answers most items on this section.
NEC 2026 250.64(C)
14. A 6 AWG copper grounding electrode conductor runs along the surface of a building and is not exposed to physical damage. What does the code require?
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B. Nothing beyond secure fastening, since it may run along the surface without metal covering or protection
At 6 AWG and larger the test is whether the run is exposed to physical damage, and where it is not the conductor may be carried along the building surface with no metal covering. Where it is exposed, the section names rigid metal conduit, intermediate metal conduit, Schedule 80 PVC, RTRC-XW, electrical metallic tubing or cable armor. Either way the conductor is securely fastened to what it runs on.
NEC 2026 250.64(B)
15. An 8 AWG copper grounding electrode conductor runs where nothing can strike it. What does the code require?
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D. Protection in one of the named raceways or in cable armor, whatever the exposure
Below 6 AWG there is no damage test at all. The section calls for rigid metal conduit, intermediate metal conduit, Schedule 80 PVC, RTRC-XW, electrical metallic tubing or cable armor either way. The hinge is the conductor size rather than the location, and an item describing a small conductor in a sheltered spot is testing exactly that.
NEC 2026 250.64(B)
16. A steel raceway is installed to protect a grounding electrode conductor. What does the code require of that raceway?
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C. That it be electrically continuous from the point of attachment to the electrode, securely fastened to ground clamps or fittings, and bonded at each end to create an electrically parallel path
An unbonded steel sleeve acts as a choke, because the changing magnetic field induces an opposing current in it and the impedance of the path climbs. Bonding both ends puts the steel electrically in parallel with the conductor instead. Nonferrous raceway does not behave this way and is not held to the requirement.
NEC 2026 250.64(E)
17. What size is the bonding jumper for a raceway or enclosure containing grounding electrode conductors?
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A. The same size as, or larger than, the largest grounding electrode conductor enclosed
The section ties the jumper to the largest conductor inside that raceway or enclosure, and it may equal it or exceed it. A fixed 6 AWG answer belongs to the rod ceiling and to the supplemental electrode jumper rather than here. Table 250.122 sizes equipment grounding conductors and has nothing to do with this jumper.
NEC 2026 250.64(E), Table 250.122
18. Aluminum grounding electrode conductors carry two distance rules that both measure 18 inches. What are they?
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B. A termination permitted within 18 inches of the bottom of a listed and identified outdoor enclosure, and no termination within 18 inches of the earth
One rule is a permission measured down from the bottom of an outdoor enclosure that is listed and identified for the environment. The other is a prohibition measured up from the earth, for conductors outside buildings or enclosures. Same number, opposite direction, so read which surface is being measured from before you answer.
NEC 2026 250.64(A)
19. Where may a bare or covered aluminum grounding electrode conductor without an extruded polymeric covering not be installed?
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D. Where subject to corrosive conditions, or in direct contact with concrete
The restriction names corrosive conditions and direct contact with concrete, and an extruded polymeric covering is what carries a conductor past it. It sits alongside the separate distance rules for terminations near the earth, and the two get remembered as one rule when they are two. Aluminum is also barred outright from being a grounding electrode, which is a third rule again.
NEC 2026 250.64(A), 250.52(B)
20. What does the code say about running a grounding electrode conductor through the ventilation, mounting or drainage openings of an enclosure?
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C. It is not permitted
A short subsection bars it outright, with no bushing or insulation relief attached. Those openings exist for air, hardware and water, and a conductor pulled through one is neither protected nor properly supported. It is a one line rule that makes a clean item.
NEC 2026 250.64(G)
21. One grounding electrode conductor is run to several electrodes. How is it sized?
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A. For the largest grounding electrode conductor required among all the electrodes it connects to
The installation subsection says the conductor is sized for the largest requirement among all the electrodes connected to it. That is the same idea the three ceilings state from the other direction, since a conductor carrying on to a demanding electrode loses its ceiling. Read the whole run for what it touches before you size any of it.
NEC 2026 250.64(F), 250.66
22. Interior metal water piping may extend the connection to an electrode within what limit?
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D. Not more than 5 feet from the point of entrance, measured along the piping
The 5 foot allowance is measured along the water piping from where it enters the building, and past that the interior piping may not be used to interconnect electrodes. An exception opens the run up in industrial, commercial and institutional buildings under qualified supervision where the piping is exposed. Five feet is the figure an item will hand you a number just above or just below.
NEC 2026 250.68(C)
23. Which materials does the code permit for a grounding electrode conductor?
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B. Copper, aluminum, copper-clad aluminum, or the items the code separately permits for extending the connection
The material section names copper, aluminum and copper-clad aluminum, and it points at the subsection that lets interior water piping and structural metal extend a connection. It also asks that the material resist the corrosive conditions at the installation, or be protected against them. Wire type conductors may be solid or stranded, and insulated, covered or bare.
NEC 2026 250.62, 250.68(C)
24. How is a grounding conductor connected to a grounding electrode?
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C. By exothermic welding, listed lugs, listed pressure connectors, listed clamps or other listed means
The connection methods section gives a short list, and every entry on it is either exothermic welding or something listed. Ground clamps are listed for both the electrode material and the conductor material, and only one conductor goes on a clamp unless the clamp is listed for more. Clamps used on buried electrodes carry a further listing for direct soil burial or concrete encasement.
NEC 2026 250.70
25. An item describes a conductor and asks which table sizes it. What settles that?
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A. What the far end of the conductor lands on
An electrode, or a point on the electrode system, means this conductor and Table 250.66 entered at the service conductor size. Anything running alongside the circuit conductors and landing on equipment is the equipment grounding conductor, from Table 250.122 entered at the device rating. Material, length and insulation change nothing about which table you open.
NEC 2026 250.66, 250.122, Table 250.66, Table 250.122
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