Short answer: Article 547 covers agricultural buildings where dust, moisture, corrosive gases from livestock waste, or animals themselves make ordinary wiring a poor fit. Its most familiar rule is the equipotential plane: in livestock areas with concrete floors where animals can touch metal equipment that could become energized, a plane of bonded metal is built into the floor (NEC 547.44(A)(1)). The plane is bonded to the grounding electrode system or to an equipment grounding terminal in the panelboard, using solid copper not smaller than 8 AWG (NEC 547.44(B)). Check the exact conditions in Article 547 in your 2026 NEC.
PSI lists Special Occupancies, Equipment and Conditions as a subject area on the Texas Journeyman exam: 6 scored NEC Knowledge questions and 3 scored Calculations questions. PSI does not say how many cover agricultural buildings. 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.
Why a barn gets its own article
Three things in farm buildings work against ordinary wiring:
| Condition | What it does to wiring |
|---|---|
| Dust from feed, hay and bedding | Builds up on equipment and can catch fire when it covers hot parts |
| Moisture and washdown | Gets into boxes and fittings and corrodes terminals |
| Corrosive gases from livestock waste | Attack metal raceways, boxes and connections over time |
Article 547 sets wiring methods, enclosures and fittings that stand up to these conditions. When you read it, ask which of the three conditions the rule is answering. That makes the rule easier to find and to remember.
Animals feel voltage people do not
Cattle, hogs and horses stand on four feet on wet concrete. A small voltage between a metal water bowl or feeder and the floor can be enough to bother them, even when a person would not notice it. Animals that avoid a water bowl drink and eat less, and that costs the farmer money.
The equipotential plane bonds the floor and the metal equipment together, so the voltage difference between what the animal stands on and what it touches stays small. That lowers the chance of current passing through the animal. It does not remove every source of stray voltage on a farm.
The equipotential plane, step by step
- Is a plane required? Look at the conditions in 547.44(A). Indoor livestock confinement areas with concrete floors need a plane where metal equipment the animals can reach may become energized (NEC 547.44(A)(1)). 547.44(A) also covers certain outdoor concrete areas, so check the full list of conditions and exceptions in your NEC.
- What is the plane? Conductive elements set in the concrete, such as wire mesh, connected together under the surface. Article 547 also has rules on how the plane is built; check them in your 2026 NEC before choosing materials.
- How is it bonded? To the building’s grounding electrode system, or to an equipment grounding terminal in a panelboard, with a solid copper conductor not smaller than 8 AWG (NEC 547.44(B)).
- What does it connect to? The metal equipment in the area, such as stalls, feeders and waterers, is bonded so it sits at the same potential as the floor.
Worked lookup. A dairy barn has a concrete floor in the milking area, metal stalls and an electric water heater feeding metal waterers that cows can reach. Assume it is an indoor livestock confinement area and the metal equipment the cows can reach may become energized. Then the area meets the conditions in 547.44(A)(1), and an equipotential plane goes in the floor. The bonding conductor from the plane runs to the equipment grounding terminal in the barn panelboard and is solid copper, 8 AWG or larger. A 10 AWG stranded conductor would not meet the rule twice: it is too small, and it is not solid.
Reading Article 547 on exam day
- Start at the scope. Decide whether the building or area is an agricultural building under this article. Not every building on a farm is.
- Find the condition. Dust, moisture, corrosion or animal contact. Each condition points to a group of rules.
- Go where the question points. Use 547.44(A) to decide where a plane is required and 547.44(B) for how it is bonded. If the question asks for a conductor size, go straight to the bonding rule: solid copper, not smaller than 8 AWG.
Check yourself
- What is the minimum bonding conductor for an equipotential plane? Solid copper, not smaller than 8 AWG.
- What may the plane be bonded to? The grounding electrode system, or an equipment grounding terminal in the panelboard.
- Why does a livestock area need an equipotential plane? To keep the voltage difference between the floor and the metal equipment animals touch small, which lowers the chance of current passing through the animal.
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Find Article 547 faster on exam day
NFPA 70, National Electrical Code, 2026 Edition (softcover). Highlight the equipotential plane trigger in 547.44(A) and the 8 AWG solid copper rule in 547.44(B), so the two halves of the rule sit side by side on the page. 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 is an equipotential plane in a barn?
Bonded conductive elements, such as wire mesh in the concrete floor, that keep the voltage difference between the floor and the metal equipment livestock can touch small.
What size wire bonds an equipotential plane?
Solid copper not smaller than 8 AWG, run to the grounding electrode system or an equipment grounding terminal in the panelboard.
Why are agricultural buildings in a separate NEC article?
Dust, moisture, corrosive gases from livestock waste and animal contact all work against ordinary wiring, so Article 547 sets methods and bonding that suit those conditions.
Are agricultural buildings on the Texas Journeyman exam?
PSI lists Special Occupancies, Equipment and Conditions as a subject area, with 6 scored NEC Knowledge questions and 3 scored Calculations questions. PSI does not say how many cover agricultural buildings.
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, Article 547
