Short answer: Every electrode listed in 250.52(A) that is present at a building must be bonded together to form the grounding electrode system (NEC 250.50). You do not pick one and ignore the others. Underground metal gas piping and aluminum are never used as electrodes (NEC 250.52(B)). A single rod, pipe or plate electrode must be supplemented by another electrode unless it has a resistance to earth of 25 ohms or less (NEC 250.53(A)(2)). The rules in this area are full of numbers to look up: lengths, sizes, depths and areas from 250.52 and 250.53.
PSI lists grounding and bonding in the Services, Service Equipment and Separately Derived Systems subject area of the Texas Journeyman exam: 6 scored NEC Knowledge questions and 4 scored Calculations questions. PSI does not say how many cover grounding electrodes alone. The Texas Journeyman Practice Pack has 1,000 original questions and 10 timed mock exams in the real two-part format, with step-by-step solutions for every calculation. Try free practice questions without signing up. Get the full pack for US$39 with one payment.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the ideas in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC, and follow your supervisor and the local inspector.
This page is a lookup drill for the electrode rules. For what grounding does and why it matters, read what electrical grounding is. For the bonding errors apprentices make at panels and subpanels, see NEC 250 grounding and bonding: 5 mistakes apprentices make.
The electrode numbers to find
| Electrode | Section | The number to know |
|---|---|---|
| Metal underground water pipe | 250.52(A)(1) | In direct contact with earth for 10 feet or more, and supplemented by another electrode (NEC 250.53(D)(2)) |
| Concrete-encased electrode | 250.52(A)(3) | Rebar at least 1/2 inch in diameter, at least 20 feet long in one piece or tied pieces, with at least 2 inches of concrete around it |
| Ground ring | 250.52(A)(4) | At least 20 feet of bare copper not smaller than 2 AWG, in contact with earth, around the building |
| Rod electrode | 250.52(A)(5) | Stainless steel or copper- or zinc-coated steel rods at least 5/8 inch in diameter, unless listed |
| Plate electrode | 250.52(A)(7) | Each plate exposes at least 2 square feet to the soil |
The 250.52(A) list also includes other electrodes, such as metal in-ground support structures. Read the full list in your NEC.
Not permitted as electrodes (NEC 250.52(B)): underground metal gas piping, aluminum, and certain swimming pool structures.
Installing the electrodes
- Plates are installed not less than 30 inches below the surface of the earth (NEC 250.53(A)(5)).
- Rods meeting rock. Where rock stops the rod, it may be driven at an angle not more than 45 degrees from vertical. Where the rock is met at an angle up to 45 degrees, the rod may instead be buried in a trench at least 30 inches deep (NEC 250.53(A)(4)(b)). Check the full rule for the required rod length.
- One rod is usually not enough. A single rod, pipe or plate needs a supplemental electrode unless it measures 25 ohms or less to earth. A rod that measures 38 ohms needs the second electrode.
- Interior water pipe. Interior metal water piping more than 5 feet from where it enters the building is not used to connect electrodes together or as part of the GEC, except in some industrial and commercial buildings (NEC 250.68(C)(1)).
Connecting the GEC
- Where it connects at the service. At any accessible point from the load end of the service drop, overhead service conductors, underground service conductors or lateral, up to and including the grounded conductor terminal or bus at the service disconnect (NEC 250.24(A)(1)).
- To which electrode. Where the electrodes are bonded together, the GEC may run to any convenient one, sized for the largest GEC required among them (NEC 250.64(F)(1)).
- Protection. A GEC smaller than 6 AWG is protected in rigid metal conduit, IMC, Schedule 80 PVC, RTRC-XW, EMT or cable armor (NEC 250.64(B)(3)).
- Ferrous raceways. A steel raceway or enclosure around a GEC is bonded at each end to the electrode or the GEC, so the raceway and the conductor form a parallel path (NEC 250.64(E)(1)).
- Accessible connections. The clamp or other connection to an electrode is accessible, except connections that are encased or buried, and exothermic or irreversible compression connections (NEC 250.68(A)).
- No solder. Connections that depend only on solder are not allowed (NEC 250.8(B)). Listed pressure connectors, listed clamps and exothermic welding are allowed.
Start with Table 250.66 to size the GEC from the service conductors. Then check 250.66(A) through (C), which cap the size where the GEC is the only connection to a rod, pipe or plate electrode, a concrete-encased electrode or a ground ring.
Worked lookup: a house with three electrodes
A new house has a metal water pipe in contact with earth for 30 feet, rebar in the footing that meets the concrete-encased rules, and one ground rod that tested at 40 ohms.
- Bond all three. All electrodes present are part of the system.
- The water pipe qualifies because it is in earth contact for 10 feet or more, and it must be supplemented. The concrete-encased electrode serves as that supplement.
- The rod alone would need a supplemental electrode at 40 ohms. Here the concrete-encased electrode is bonded into the same system and serves as that supplement, so another rod is not needed just because the rod measured 40 ohms. Check the supplemental electrode rules in 250.53 in your NEC.
- The GEC can run to the most convenient electrode, sized for the largest GEC required for any of them.
Check yourself
- Can underground gas piping serve as an electrode? No.
- How deep is a plate electrode installed? At least 30 inches.
- A ground ring uses what minimum copper size? 2 AWG.
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Find 250.50 to 250.53 faster on exam day
NFPA 70, National Electrical Code, 2026 Edition (softcover). Highlight every length, diameter, depth and ohm value in 250.52 and 250.53, so each number is quick to find. The Texas exam is open book. PSI allows a soft-bound NEC with highlighting, underlining and notes made in advance. Loose-leaf, spiral-bound and ring-bound copies are not allowed, and only permanent index tabs made or supplied by the NEC publisher are permitted; homemade and third-party tabs are not.
FAQ
What does NEC 250.50 require?
All the electrodes listed in 250.52(A) that are present at a building must be bonded together to form the grounding electrode system.
Is one ground rod enough?
A single rod can stand alone only if its resistance to earth is 25 ohms or less. Otherwise, it must be supplemented by another qualifying electrode, which does not have to be a second rod. Any other electrodes present at the building are still bonded into the system.
What cannot be used as a grounding electrode?
Underground metal gas piping, aluminum and certain swimming pool structures.
How must a small GEC be protected?
A GEC smaller than 6 AWG is protected in RMC, IMC, Schedule 80 PVC, RTRC-XW, EMT or cable armor.
Are grounding electrodes on the Texas Journeyman exam?
PSI lists grounding and bonding in Services, Service Equipment and Separately Derived Systems: 6 scored NEC Knowledge questions and 4 scored Calculations questions.
Sources checked October 2026
- PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70, National Electrical Code, 2026 Edition, 250.8, 250.24, 250.50, 250.52, 250.53, 250.64, 250.66 and 250.68
