Written against the 2026 NEC and checked section by section, September 2026
Grounding Electrodes Practice Questions
Three sections carry this whole topic, and telling them apart is most of the work. 250.50 asks what is present at the building and bonds all of it together, 250.52 says what a thing has to be before it counts, and 250.53 says what you have to do with it once it does. These 25 items lean on the qualifying conditions inside each electrode entry, the installation rules for rods and rings, and the 25 ohm sentence read the way it is actually written, as an exception to a requirement rather than a requirement of its own.
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 electrodes study page first if the topic is new to you.
1. A building has a metal underground water pipe in earth contact for 30 feet, reinforcing steel in the footing, and a driven rod. What does the grounding electrode system section require?
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D. That all three be bonded together to form one grounding electrode system
The section is not a menu. Every qualifying electrode present at the building or structure served is bonded together into one system. An option offering you the best one is the distractor this section exists to catch, and the word present is what does the work.
NEC 2026 250.50
2. A new building has none of the qualifying electrodes. What does the code require?
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B. One or more of the electrodes the section names for installation
Where none of the qualifying electrodes exists, the section calls for one or more from the shorter list it names to be installed and used. That is the only situation in which anybody picks an electrode. Which subdivisions bound that shorter list has moved between editions, so read the range in your own book rather than reciting a letter.
NEC 2026 250.50, 250.52(A)
3. A concrete encased electrode exists in an older building but the reinforcing steel cannot be reached without breaking the concrete. What does the code allow?
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A. It is not required to be part of the grounding electrode system
The section carries one exception, and it releases concrete encased electrodes in existing buildings where the rebar is not accessible without disturbing the concrete. New work gets no such relief, which is the half items are built on. Nothing in the exception asks for a measurement or names a substitute.
NEC 2026 250.50
4. A metal underground water pipe is in direct contact with the earth for 8 feet. Is it a grounding electrode?
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C. No, the entry calls for 10 feet or more of direct earth contact
Each entry in the electrode list is a description with a condition inside it, and the condition is the entry. Ten feet of direct earth contact is the threshold for the water pipe, and continuity to the point of connection is a second condition stacked on top. A stem handing you a figure just under the threshold is asking whether you read to the end of the sentence.
NEC 2026 250.52(A)(1)
5. What does the code require for a metal in-ground support structure to qualify as an electrode?
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D. Direct contact with the earth vertically for 10 feet or more, with or without concrete around it
That entry covers pilings, casings and other structural metal, and its test is vertical earth contact of 10 feet or more. Concrete around it neither helps nor hurts, because the entry says with or without encasement. Where several qualify at one building, bonding only one of them into the system is permitted.
NEC 2026 250.52(A)(2)
6. A concrete encased electrode is built from bare copper rather than from rebar. What does the entry require?
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A. At least 20 feet of bare copper not smaller than 4 AWG
The copper version of the footing electrode runs at least 20 feet and is no smaller than 4 AWG, and it is bare. Two AWG is the ground ring conductor, a separate entry with a different job. Both are 20 foot rules, which is exactly why their wire sizes get swapped.
NEC 2026 250.52(A)(3), 250.52(A)(4)
7. How much concrete has to cover the metal of a concrete encased electrode, and where does that concrete have to sit?
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B. Two inches, in a footing or foundation that is itself in direct contact with the earth
The entry asks for at least 2 inches of concrete around the metal, and that concrete has to be in a footing or foundation in direct contact with the earth, or in a vertical foundation member meeting the same test. The second condition is where real buildings fail, since a slab poured over a vapor barrier has concrete and steel and no path to earth. The 2026 edition restored an informational note naming insulation and vapor barriers among the things that get in the way.
NEC 2026 250.52(A)(3)
8. A building sits on twelve footings, each holding a qualifying concrete encased electrode. How many have to be bonded into the grounding electrode system?
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C. One
The entry says that where multiple concrete encased electrodes are present at a building or structure, bonding only one of them into the system is permitted. So twelve qualifying footings produce one required connection and eleven the code declines to ask for. The metal in-ground support structure entry carries the same permission.
NEC 2026 250.52(A)(3), 250.52(A)(2)
9. What does the ground ring entry require?
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D. At least 20 feet of bare copper no smaller than 2 AWG, encircling the building or structure and in direct contact with the earth
Three conditions ride on that entry: a length of at least 20 feet, a conductor no smaller than 2 AWG bare copper, and a path that encircles the building or structure in direct earth contact. Four AWG belongs to the copper version of the footing electrode. Keeping the two 20 foot entries apart is most of what this pair of questions asks.
NEC 2026 250.52(A)(4), 250.52(A)(3)
10. A pipe or conduit is used as a grounding electrode. What is the minimum trade size?
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A. Trade size 3/4
The rod and pipe entry sets trade size 3/4 as the floor for a pipe or conduit electrode, and where the pipe is steel it is galvanized or otherwise metal coated against corrosion. Rod type electrodes are governed by diameter instead. Both kinds have to be at least 8 feet long, which is a separate condition on the same entry.
NEC 2026 250.52(A)(5)
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. A rod electrode does not carry a listing. What is the minimum diameter?
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C. Five eighths of an inch
An unlisted rod of stainless steel, or of copper or zinc coated steel, is at least five eighths of an inch across. A listed rod may be smaller, which is why the entry says unless listed. The 8 foot length applies either way.
NEC 2026 250.52(A)(5)
12. What surface does a plate electrode have to expose?
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B. Two square feet of surface to exterior soil
The entry asks for at least 2 square feet of surface exposed to exterior soil. Thickness then depends on the metal, a quarter inch for bare or conductive coated iron or steel plates and thinner for solid uncoated nonferrous ones. Burial depth is an installation matter handled in the next section over.
NEC 2026 250.52(A)(7), 250.53
13. Which of these is named as not permitted for use as a grounding electrode?
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D. Metal underground gas piping systems
Three things are barred by name: metal underground gas piping systems, aluminum, and the structures and reinforcing steel described in the swimming pool rules. Gas piping catches people because a metal gas line does get bonded, and bonding a line that could become energized is a separate obligation that does not turn it into an electrode. An option offering underground gas piping is wrong however the rest of the scenario reads.
NEC 2026 250.52(B)
14. Why is aluminum on the list of things that may not be a grounding electrode?
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A. The code bars it outright, with no condition attached
The exclusion is unconditional, which sets it apart from the separate aluminum restrictions on the grounding electrode conductor, where corrosive conditions and concrete contact are the trigger. Two different rules about the same metal in the same article get remembered as one. Read which conductor or component the rule in front of you is written about.
NEC 2026 250.52(B), 250.64(A)
15. Rod, pipe and plate electrodes go below the permanent moisture level. How strong is that requirement?
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C. It applies where it is practicable
The section conditions that one on practicability, which is unusual enough to be worth noticing. In the same breath it asks that these electrodes be free of nonconductive coatings such as paint or enamel, and that half carries no such condition. Reading the qualifier is the whole of this item.
NEC 2026 250.53
16. Rock bottom stops a rod before it reaches 8 feet vertically. What does the code permit first?
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B. Driving the rod at an oblique angle of not more than 45 degrees from vertical
The relief comes in order. First the rod may go in at an angle of not more than 45 degrees off vertical, and only where rock stops it at that angle too does it go into a trench at least 30 inches deep. The 2026 edition restructured that subdivision so the vertical case is stated first and the relief follows as two exceptions. Reaching for the trench first skips a step the code sets out in sequence.
NEC 2026 250.53(A)(4)
17. The upper end of a driven rod finishes above ground level. What does the code require?
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A. That the aboveground end and the conductor attachment be protected against physical damage
The rule reads flush with or below ground level unless the aboveground end and the point where the conductor attaches are protected against damage. So a rod left proud is not automatically a violation, but the protection has to be there. Paint would violate a different sentence in the same section, which keeps nonconductive coatings off the electrode.
NEC 2026 250.53(A)(4), 250.10
18. Rod, pipe or plate electrodes of one grounding system sit near those of another system. What spacing does the code set?
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D. Not less than 6 feet from any other electrode of another grounding system
The spacing subsection sets 6 feet between electrodes of different grounding systems, and it names strike termination device electrodes among the systems it reaches. Twice the length of the longest rod is an informational note about paralleling efficiency rather than a requirement. That note explains why more spacing helps and it does not set the number.
NEC 2026 250.53
19. A footing electrode is the only electrode at a building. Does the 25 ohm sentence apply?
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C. No, that sentence is written about a single rod, pipe or plate electrode
The measurement is an exception to the supplemental electrode requirement, and that requirement is written about a single rod, pipe or plate electrode. With no rod, pipe or plate in the system there is nothing to supplement and no measurement to make. An option offering a resistance test here is aimed at candidates who learned the rule as a system requirement, which it has never been.
NEC 2026 250.53(A)(2)
20. Two rods are driven 6 feet apart and bonded together at a service. What does the supplemental electrode rule ask for next?
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B. Nothing further, because the supplement is already installed
The supplement is the requirement and the measurement is the way out of it, so once a second electrode is in the ground there is nothing left to prove. The section does not then ask for the pair to be measured. That is why driving two and moving on is not a shortcut around the code, it is the code read the way that avoids having to demonstrate anything.
NEC 2026 250.53(A)(2), 250.53
21. A metal underground water pipe is used as an electrode. What else does the code require?
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A. A supplemental electrode of another type, with no measurement offered as a way out
The water pipe subdivision carries a supplemental electrode requirement with no resistance exception attached, and that is the difference between the water pipe and the rod. The supplement comes from the rest of the electrode list, so a second water pipe does not satisfy it. The reason is custodial rather than electrical, since the pipe is the one electrode somebody else owns and can replace with plastic.
NEC 2026 250.53(D)
22. What does the water pipe subdivision say about continuity of the grounding path to interior piping?
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D. It may not rely on water meters, filtering devices or similar equipment
The first half of that subdivision says the grounding path or the bonding connection to interior piping does not depend on a water meter, a filtering device or similar equipment. Those are the parts somebody removes on a Tuesday, so the path is made around them. The second half of the same subdivision is the supplemental electrode requirement.
NEC 2026 250.53(D)
23. Bonding jumpers used to tie grounding electrodes together are sized how, and what may not serve as one?
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C. Sized in accordance with 250.66, and rebar may not be used as a conductor to interconnect electrodes
The bonding jumper subdivision points at the electrode conductor sizing section for the size, at the installation rules for how it is run, and at the connection methods section for how it lands. It then says plainly that rebar is not used as a conductor to interconnect the electrodes of grounding electrode systems. Table 250.122 sizes equipment grounding conductors and answers a different question.
NEC 2026 250.53(C), 250.66, 250.70
24. An auxiliary grounding electrode is connected to an equipment grounding conductor. What does the code say about it?
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B. It is not required to meet the electrode bonding requirements or the resistance condition, and the earth is still not an effective ground fault current path
Auxiliary electrodes are permitted and they are released from the bonding requirements and from the resistance condition that governs supplemental electrodes. What the section will not allow is treating the earth as the fault current path, which is stated in the performance rules and repeated here. So an auxiliary electrode adds something and replaces nothing.
NEC 2026 250.54, 250.4(A)(5)
25. A stem hands you a dimension, such as a length of pipe or a length of rebar. Which section is it testing?
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A. The electrode qualification section, because the dimension decides whether the thing described is an electrode at all
A dimension in the stem is almost always the qualifying condition inside one of the entries in the electrode list, and the figure given will sit just over or just under it. A stem that lists what is present at the building is the system section instead, and a stem about driving, spacing, depth or angle is the installation section. Sorting the three takes seconds and saves a lookup in the wrong place.
NEC 2026 250.52(A), 250.50, 250.53
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