NEC 675 Irrigation Machines for the Journeyman Exam: Center Pivot Equivalent Current Rating, Disconnects, Grounding and Collector Rings

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.

Where this fits

General motor sizing (125 percent of the largest motor plus the rest) is on NEC 430 motor calculations. Article 675 changes that recipe for one kind of equipment. Center pivots are used across Texas agriculture. For the Journeyman exam, focus on recognizing when Article 675 applies, finding its equivalent current formulas, and identifying its disconnect, grounding and bonding rules.

The parts of Article 675

• General rules (Part I). These apply to all electrically driven or controlled irrigation machines. They cover the machine’s lighting and control circuits, the marking on the main control panel, the disconnecting means, the collector rings, the raceways and cables on the machine, and the grounding and bonding of the structure.
• Center pivot machines (Part II). Additional rules for machines that rotate about a central pivot point (NEC 675.21). This is where the equivalent current rating sits.

The equivalent current rating

Each tower motor runs only part of the time to keep the machine in line. Article 675 accounts for that intermittent duty when it sets the equivalent current ratings, and the result can be lower than the ordinary multiple-motor calculation in Article 430. The equivalent current is the rating that the article’s conductor, controller and disconnect rules are then applied to.

Rating	What it is used for	How to find it
Equivalent continuous current	Sizing the conductors and the controller current rating	125% of the largest motor full-load current + 60% of the full-load currents of all other motors
Equivalent locked-rotor current	Sizing the controller and disconnect for starting	2 × the largest motor locked-rotor current + 80% of the full-load currents of all other motors

For a center pivot, calculate the equivalent continuous current (NEC 675.22(A)) and the equivalent locked-rotor current (NEC 675.22(B)) from Part II of Article 675, then apply those values to the conductor, controller and disconnect requirements instead of the motor-by-motor sum from Article 430.

Disconnect, grounding and bonding

• Main disconnect. The main disconnecting means is located at the point where power connects to the machine or is visible from the machine, is readily accessible and can be locked in the open position. Its current and horsepower ratings are not less than those required for the main controller. The article also sets overcurrent protection requirements tied to the main disconnecting means; read them in your 2026 NEC. Motors and controllers on the machine also have their own disconnecting means as the article requires.
• Grounding. Electrical equipment on the machine that requires grounding, such as the main control panel and motor frames, is connected to an equipment grounding conductor provided as part of each cord, cable or raceway on the machine. Article 675 has its own minimum size rule for that conductor on the machine, so check it in your 2026 NEC instead of relying on the general Article 250 sizing table alone.
• Bonding. The machine’s metal structure, metal raceways and cable sheaths are bonded to the equipment grounding conductor, so a fault has a continuous path back to the source.
• Lightning. Where the machine has a stationary point, a grounding electrode system is connected at that point for lightning protection.
• Collector rings. A center pivot uses collector rings to pass power from the fixed pivot to the turning machine. Their rules are in the general part of the article (Part I). When you look them up, separate the rings used for power, for control or signaling, and for grounding, because their rating rules are not identical, and check the enclosure rules for protection from the weather and accidental contact.

Worked example: equivalent continuous current

A center pivot runs on 480 V three-phase. Its largest motor is 5 hp with a nameplate full-load current of 7.6 A, and eight tower motors each have a nameplate full-load current of 2.4 A. Both currents are given data for this example, so use them as stated rather than looking up table values. Find the equivalent continuous current.

1. Largest motor. 7.6 × 1.25 = 9.5 A.
2. All other motors. 8 × 2.4 = 19.2 A. 19.2 × 0.60 = 11.52 A.
3. Total. 9.5 + 11.52 = 21.02 A, about 21 A.

The key difference from the ordinary Article 430 multiple-motor method is the 60 percent factor on the other motors. For the general motor calculation, see the linked Article 430 lesson.

Worked example: equivalent locked-rotor current

Use the same machine. The largest motor has a locked-rotor current of 46 A.

1. Largest motor. 46 × 2 = 92 A.
2. All other motors. 19.2 × 0.80 = 15.36 A.
3. Total. 92 + 15.36 = 107.36 A, about 107 A.

Check yourself

1. What percentage of the largest motor’s full-load current goes into the equivalent continuous current? 125 percent.
2. What percentage of the other motors’ full-load currents goes into the equivalent continuous current? 60 percent.
3. How is the largest motor counted in the equivalent locked-rotor current? 2 times its locked-rotor current.
4. Which part of Article 675 has the equivalent current rating? Part II, center pivot machines.

FAQ

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, Articles 430 and 675