Quick Hits

Episode 4: Center Pivot Special Formulas & Equivalent Ratings (675.21 – 675.22)

SLIDE 1 (HOOK / COVER)

⚡ NEC Quick Hit: Center Pivot Sizing Formulas (Part 4 - Article 675) ⚡

Center pivot towers don't all run simultaneously—they cycle on and off as the span rotates. Part II of Article 675 gives us special reduced derating formulas specifically for center pivots! Let's wrap up Article 675! 👇

SLIDE 2 (CENTER PIVOT CONTINUOUS-CURRENT FORMULA)

The 60 Percent Derating Rule:

• Sizing Branch-Circuit Conductors & Devices:
  $$\text{Continuous Current Rating} = (125\% \times \text{Largest Motor FLA}) + (60\% \times \sum \text{Remaining Motors FLA})$$

• Why reduced? Because center pivot tower motors step and pulse in sequence to maintain alignment rather than running continuously together!

SLIDE 3 (CENTER PIVOT LOCKED-ROTOR FORMULA)

Calculating Inrush Demand:

• Selection of Controllers & Disconnects:
  $$\text{Locked-Rotor Current} = (2 \times \text{Largest Motor LRA}) + (80\% \times \sum \text{Remaining Motors FLA})$$

• This calculated value is used to select the required horsepower rating from NEC Tables 430.251(A) and (B).

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: Don't confuse general irrigation calculations with Center Pivot formulas! Using the 60% factor for remaining motors (675.22(A)) instead of full duty-cycle math saves wire size and conduit cost while keeping the installation 100% Code compliant!

💬 Save this post for your final code review on irrigation machines!

🔗 More code breakdowns and study tools at www.JoshTheSparky.com

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