Checked against primary sources 2026-08-24

Grounding Electrodes, NEC 250.52: What Qualifies and What You Must Use

You do not choose an electrode. You use what the building already has. The rule is not pick one. It is bond together everything present at the building, then add if what is present is not enough. Three sections carry the whole topic.

Test yourself: 25 free questions on this topic

Try it hands-on: Grounding electrode lab

The grounding electrode system, in one paragraph

A grounding electrode system is not one electrode. It is every qualifying electrode that happens to be present at the building or structure served, bonded together so that they act as one (NEC 250.50). A metal underground water pipe, footing steel, a metal in-ground support structure, a ground ring, a driven rod: if it is there and it fits the description in 250.52(A), it belongs to the system and gets connected in. Only where none of them is present do you install anything, and the code then names a shorter range of types to install (NEC 250.50). That one idea decides most items on this subject, because the wrong answer on offer is usually the one that invites you to pick a single electrode out of the set.

The sentence the article turns on

Every grounding electrode present at a building or structure served gets bonded together with the others to form one grounding electrode system (NEC 250.50).

Present is the word doing the work. A house with a metal underground water pipe, reinforcing steel in the footing and a driven rod out back has all three in its system. Not the best one. All of them, tied to each other.

Where none of the qualifying electrodes is present, one or more of them gets installed (NEC 250.50). That is the only situation in which anybody picks an electrode, and it is why a rod is what you drive when the building offers nothing, rather than a default.

The list in 250.52 is not a ranking of quality. What 250.50 does is split it into two ranges: one set counts as part of the system whenever it happens to be there, and a shorter set is what you install when none of the first set exists. The letters bounding those two ranges have moved from one edition of the code to the next, so read the ranges in your own copy rather than from a number you remember.

One release is written into the section. A concrete-encased electrode in an existing building does not have to be brought into the system where the reinforcing steel cannot be reached without disturbing the concrete (NEC 250.50). New work gets no such relief, which is the half of the exception that items are built on.

What qualifies, and the condition attached to each one

Each entry in 250.52(A) is a description with a condition inside it, and the condition is the whole entry. A metal water pipe is not an electrode. A metal water pipe in contact with earth for a stated distance is.

• Metal underground water pipe, in direct contact with the earth for 10 feet or more, and electrically continuous to the point where the conductor lands on it (NEC 250.52(A)(1)).
• Metal in-ground support structure, in direct contact with the earth vertically for 10 feet or more, with or without concrete around it (NEC 250.52(A)(2)). Pilings and casings count.
• Concrete-encased electrode, at least 20 feet of half-inch or larger steel reinforcing bar, or at least 20 feet of bare copper no smaller than 4 AWG, encased in concrete that is itself in contact with the earth (NEC 250.52(A)(3)).
• Ground ring, at least 20 feet of bare copper no smaller than 2 AWG, encircling the building or structure and in direct contact with the earth (NEC 250.52(A)(4)).
• Rod and pipe electrodes, at least 8 feet long. A rod is at least five eighths of an inch across unless it carries a listing, and a pipe or conduit electrode has a minimum trade size of its own (NEC 250.52(A)(5)).
• Plate electrode, exposing at least 2 square feet of surface to exterior soil, with a minimum thickness that depends on whether the plate is ferrous (NEC 250.52(A)(7)).
• Other listed electrodes, and other local metal underground systems such as piping systems, tanks and well casings (NEC 250.52(A)(6), NEC 250.52(A)(8)).

Read those conditions as tests you apply to the building in front of you. Ten feet of pipe. Twenty feet of steel. Eight feet of rod. Two square feet of plate. An item that hands you a nine foot run of metal water pipe is not asking about grounding at all, it is asking whether you read to the end of the sentence.

What encased actually asks for

The concrete-encased electrode carries more conditions than any of the others, and the trade name Ufer hides most of them.

Two inches of concrete around the steel, and the concrete has to be in a footing or foundation that is itself in direct contact with the earth (NEC 250.52(A)(3)). The steel can run horizontally near the bottom of the footing or vertically inside a foundation or structural member that meets the same test.

That second condition is where real buildings fail it. A slab poured over a vapor barrier, or a footing separated from soil by rigid foam, has concrete and has steel and has no path to earth. For the 2026 edition NFPA restored and revised the informational note under this subdivision specifically to say what direct contact with the earth means, naming insulation and vapor barriers among the things that get in the way. A note explains rather than requires, but it tells you how the panel reads the sentence above it.

Twenty feet is a length, not a piece. One continuous twenty foot bar qualifies, and so does a run made up of shorter bars tied together with the usual steel tie wire, welded, or joined by other effective means (NEC 250.52(A)(3)).

Then the exception that decides items in both directions: where more than one qualifying concrete-encased electrode is present at a building, only one of them has to be bonded into the grounding electrode system (NEC 250.52(A)(3)). So a building on twelve footings is not a building with twelve grounding electrode connections. It is a building with one, and eleven the code declines to ask for.

How 250.53 puts them in the ground

250.52 says what a thing has to be. 250.53 says what you have to do with it, and the two get confused because both contain distances.

• A rod or pipe electrode is installed so that at least 8 feet of its length is in contact with the soil, driven vertically to that depth (NEC 250.53(A)(4)).
• Where rock stops it, the electrode is permitted to go in at an angle up to 45 degrees off vertical, and where rock stops it at that angle too, it goes in a trench at least 30 inches deep (NEC 250.53(A)(4)).
• The upper end of a rod finishes flush with or below ground level, unless the aboveground end and the point where the conductor attaches are protected against physical damage (NEC 250.53(A)(4)).
• Rod, pipe and plate electrodes go below the permanent moisture level where that is practicable, and they are free of nonconductive coatings such as paint or enamel (NEC 250.53).
• Where more than one rod, pipe or plate electrode is used, they sit at least 6 feet apart (NEC 250.53).
• A ground ring and a plate electrode each have a minimum burial depth stated in the section. Look both up in your own book.

The rod and pipe rules are the ones that moved this cycle. NFPA restructured that subdivision for the 2026 edition so that the vertical eight foot installation is stated first and the rock-bottom relief follows it as two exceptions rather than as running text. The requirements are the same requirements. What changed is that a candidate reading down the page now meets the general case before the escape from it, which is the order the exam asks the question in.

Ground rods: the rules people search for

Four numbers carry nearly every rod question and they sit in two sections.

• Length. A rod or pipe electrode is not less than 8 feet long (NEC 250.52(A)(5)). A rod of stainless steel or of copper or zinc-coated steel is at least five eighths of an inch across unless it is listed, and a pipe or conduit electrode has a minimum trade size of its own.
• Depth. At least 8 feet of the electrode has to be in contact with the soil, and the electrode is driven vertically to a depth of not less than 8 feet (NEC 250.53(A)(4)). The upper end finishes flush with or below ground level unless the aboveground end and the conductor attachment are protected against physical damage.
• Spacing. Where more than one rod, pipe or plate electrode is installed to satisfy the section, they sit not less than 6 feet apart (NEC 250.53(A)(3)). A separate rule keeps an electrode of one grounding system at least 6 feet from an electrode of another grounding system (NEC 250.53(B)).
• The second rod. A single rod, pipe or plate electrode is supplemented by an additional electrode, and the exception releases you only where that single electrode measures 25 ohms or less to earth (NEC 250.53(A)(2)). Requirement first, measurement second, which is the section below in one line.

Rock is the other case people search for, and the code answers it in two steps. Where rock bottom is encountered, the electrode may be driven at an oblique angle not exceeding 45 degrees from the vertical. Where rock bottom is encountered at that angle as well, it may be buried in a trench at least 30 inches deep (NEC 250.53(A)(4)).

Both of those are written as exceptions under the vertical rule, so the reading order is the general case and then the way out of it. That is also the order an item asks it in, which is why a candidate who learned the angle first tends to answer the angle to a question about an ordinary rod.

The twenty-five ohm sentence, read the way it is written

The most misquoted line in Article 250 is the one people summarize as a grounding electrode system having to measure 25 ohms or less. No such requirement exists anywhere in the article.

What the section says is that a single rod, pipe or plate electrode gets supplemented by an additional electrode, and then an exception says the supplemental electrode is not required where that single electrode has a resistance to earth of 25 ohms or less (NEC 250.53(A)(2)).

Direction is everything here. The requirement is the second electrode. The measurement is the way out of the requirement, and an exception only helps somebody who can show its condition is met. That is why an installer who drives two rods and never owns a meter is compliant, and why an installer who drives one rod is relying on a number nobody wrote down.

What the sentence does not reach

It is written about a single rod, pipe or plate electrode. It is not written about a concrete-encased electrode, a ground ring, a metal underground water pipe, or a pair of rods already bonded to each other.

Work it against four buildings and it stops being slippery.

1. A footing electrode and nothing else. There is no rod, pipe or plate in the system, so there is nothing to supplement and 25 ohms never enters the analysis. An answer choice offering a resistance test is there for people who learned the rule as a system requirement.
2. Two rods, 6 feet apart, bonded together. The supplement is satisfied by what was installed. No measurement is called for, and none of the answer choices about ohms applies.
3. One rod, measured, reading above 25 ohms. Add the second electrode. The section does not then ask you to measure the pair, because once the supplement is installed the exception is no longer the thing you are relying on.
4. A metal water pipe supplemented by one driven rod. The rod is still a single rod, pipe or plate electrode, and the subdivision is written about what the electrode is rather than about the job it was brought in to do. Read it that way and the second rod is the safe answer.

Driving two and moving on is not a shortcut around the code. It is the code, taken at the reading that avoids having to prove anything.

The water pipe is the one with no way out

A metal underground water pipe gets supplemented by an additional electrode of another type, and no resistance measurement excuses it. That rule sits under the subdivision titled Metal Underground Water Pipe (NEC 250.53(D)), and finding it by that title is safer than finding it by the letter. It is the difference between the water pipe and the rod, and it is worth holding on its own.

The supplement can be any of the other qualifying types. It cannot be a second metal water pipe, because the subdivision sends you past that entry in the list on its way to the others.

The reason is not electrical, it is custodial. The water pipe is the only electrode in the set that somebody else owns and somebody else maintains. A plumber replaces twenty feet of galvanized with plastic on a Tuesday and the electrode quietly stops existing, with nothing on the panel to say so. A system leaning on a pipe you do not control needs a second leg that you do, and that is why this subdivision has no measurement in it.

What does not count

Three things are named as not permitted for use as grounding electrodes: metal underground gas piping systems, aluminum, and the structures and reinforcing steel of a swimming pool (NEC 250.52(B)).

Gas piping is the one that catches people, because the intuition runs the other way and because a gas line does get bonded. Bonding a metal gas line that is likely to become energized is a separate obligation written elsewhere in Article 250, and satisfying it does not turn the line into an electrode. An answer choice offering underground gas piping as part of a grounding electrode system is wrong however the rest of the scenario reads.

Aluminum is excluded outright, which sits alongside the separate aluminum restrictions on the grounding electrode conductor and gets remembered as one rule when it is two. And anything not on the list and not listed as an electrode simply is not one, because there is no general permission for a made electrode that seems as good.

Electrode versus electrode conductor

An electrode is the metal in the ground, and everything on this page is about what qualifies as one and how it goes in. The grounding electrode conductor is the wire that connects the system to that metal, and it is sized from a different table on a different input, which is the subject of the page on the grounding electrode conductor.

Reading an item on this topic

These items are short and they are decided by one word in the stem. The four tells are worth knowing cold.

• A stem that lists what is at the building is a 250.50 item. Count the electrodes and bond all of them. If an option offers you the best one, that option is the distractor.
• A stem that gives you a dimension is a 250.52 item. It wants to know whether the thing described qualifies at all, and the number in the stem is either just over the threshold or just under it.
• A stem that describes driving, spacing, depth or angle is a 250.53 item. The electrode already qualifies. The question is about the installation.
• A stem that mentions ohms is testing whether you know the measurement is an exception rather than a requirement. Check what kind of electrode it is attached to before you do anything else.

None of it is memorization work. The three sections sit within a couple of pages of each other, so tab 250.50 and read forward.

Questions people ask

What is a grounding electrode system?

Every grounding electrode present at a building or structure served, bonded together so they work as one system (NEC 250.50). It is not a choice between electrode types, and there is no ranking of quality in the list. Where none of the qualifying electrodes exists at the building, one or more of a shorter range of types is installed and used instead.

What qualifies as a grounding electrode?

NEC 250.52(A) describes eight of them and each description carries a condition inside it: a metal underground water pipe in earth contact for at least 10 feet, a metal in-ground support structure in vertical earth contact for at least 10 feet, a concrete-encased electrode, a ground ring, a rod or pipe electrode, another listed electrode, a plate electrode, and other local metal underground systems or structures such as piping, tanks and well casings that are not bonded to a metal water pipe. The condition is the whole entry, so a nine foot run of metal water pipe is not an electrode. NEC 250.52(B) then rules three things out by name, metal underground gas piping and aluminum among them.

How deep does a ground rod have to go?

At least 8 feet of the electrode has to be in contact with the soil, and NEC 250.53(A)(4) has it driven vertically to a depth of not less than 8 feet. The rod itself is not less than 8 feet long under NEC 250.52(A)(5), so there is nothing spare to leave standing above grade. The upper end finishes flush with or below ground level unless the aboveground end and the point where the conductor lands are protected against physical damage.

When do you need a second ground rod?

Whenever the system leans on a single rod, pipe or plate electrode. NEC 250.53(A)(2) requires that electrode to be supplemented by an additional one, and the only way out is the exception, which releases you where the single electrode measures 25 ohms or less to earth. Nothing in Article 250 asks a system to reach 25 ohms, so the measurement is an escape from the second electrode rather than a target. Where two or more rods are installed to satisfy the section they go at least 6 feet apart, under NEC 250.53(A)(3).

What surface area must a plate electrode have?

Each plate electrode has to expose not less than 2 square feet of surface to exterior soil (NEC 250.52(A)(7)). Thickness is set separately in the same subdivision, and the figure for iron or steel plates is not the figure for solid uncoated nonferrous ones, so read both halves of it in your own book. NEC 250.53(A)(5) then buries the plate not less than 30 inches below the surface of the earth.

What if a ground rod cannot be driven vertically?

NEC 250.53(A)(4) answers it in two steps, both written as exceptions under the vertical rule. Where rock bottom is encountered, the electrode may be driven at an oblique angle not exceeding 45 degrees from the vertical. Where rock bottom is encountered at that angle as well, it may be buried in a trench at least 30 inches deep. An item on this normally hands you the obstruction and expects the steps in that order.

Does a metal in-ground support structure count as a grounding electrode?

Yes, where it is in direct contact with the earth vertically for 10 feet or more, with or without concrete encasement (NEC 250.52(A)(2)). The informational note under it names pilings, casings and other structural metal as examples. Where several of them are present at one building, the subdivision permits bonding only one into the grounding electrode system.

Is the metal water pipe electrode optional?

No. Where a qualifying metal underground water pipe is present at the building it is part of the grounding electrode system and gets bonded in with the rest (NEC 250.50). It also has to be supplemented by an additional electrode of another type under NEC 250.53(D), and no resistance measurement excuses that supplement, which is the difference between the water pipe and a single rod. The supplement can be any of the other qualifying types, because the subdivision sends you past the water pipe entry on its way through the list.

What this page cites

• NEC 250.50 Grounding electrode system. Every qualifying electrode present at a building or structure served is bonded together into one system, and where none is present one or more is installed. The section names two ranges of 250.52(A) subdivisions and those ranges have moved from one edition to another, so they are deliberately not printed here. source
• NEC 250.52 Electrodes permitted for grounding, and in 250.52(B) the three that are not. Each entry is a description plus a qualifying condition, and the condition is the part exam items are built on. source
• NEC 250.52(A)(3) Concrete-encased electrode. NFPA code-making panel 5, second revision 8138 for the cycle that produced the 2026 edition, restores and revises the informational note under this subdivision to explain what direct contact with the earth means, naming insulation and vapor barriers among the things that hinder it. source
• NEC 250.53 Grounding electrode system installation. Second revision 8235 in the same panel 5 draft restructures the rod and pipe subdivision at 250.53(A)(4), putting the vertical eight foot installation first and the rock-bottom relief behind it as exceptions. No revision in that draft touches the supplemental electrode subdivision, and the phrase 25 ohms does not appear in the document at all. source
• NEC 250.53(A)(4) Rod and pipe electrodes, including the upper end finishing flush with or below ground level unless the aboveground end and the conductor attachment are protected. Address confirmed independently in EC&M Code Q&A and in Electrical Contractor Magazine on the 2026 Chapter 2 changes. source
• NEC 250.53(D) Metal underground water pipe. The supplemental electrode sentence is reproduced in two separate forums.mikeholt.com threads filed under this citation, and the requirement itself is corroborated by EC&M. The subdivision letter has one clean source, so the page names the subdivision by its title as well. source
• NEC 250.53(A)(2) The supplemental electrode requirement and the 25 ohm exception. Address taken from EC&M, which heads that content 250.53(A)(2), and corroborated by NFPA code-making panel 5, whose first draft for this cycle carries the identical sentence at the matching position inside the new article for systems over 1000 volts. source
• NEC 250.10 Protection of ground clamps and fittings, which is where 250.53(A)(4) sends you when a rod finishes above grade.
• NEC 250.66 Sizing the conductor that reaches these electrodes, and the three ceilings that cap the table depending on which electrode is at the far end. Covered on the grounding electrode conductor page rather than here.