Quick Hits

⚡ NEC Article 120 — Load Calcs Won't Kill You

🚜 Episode 39 — Farm Buildings: The 60-Amp Tiers

Article: 120 — Load Calculations
Part: Part V — Farm Loads
Section: 120.102(B)
Format: Quick Hit

🎯 What You'll Learn

Farm buildings can have very different electrical loads than typical commercial or residential buildings. Section 120.102(B) provides demand-factor rules for feeders and services supplying farm buildings with multiple branch circuits.

The key idea: the first portion of the load gets calculated at 100%, the next 60 amperes gets a 50% demand factor, and additional tiers may apply.

📖 The Quick Hit

🏚️ Farm Building Loads

When a feeder or service supplies a farm building — or another farm load — with two or more separate branch circuits, Table 120.102(B) provides demand factors that can be applied to the load.

Instead of simply treating every connected load as though it will operate simultaneously, the table recognizes that farm equipment won't necessarily all operate at the same time.

⚡ The 100% Baseline

The first step is determining the greatest of these:

1️⃣ All loads expected to operate simultaneously

2️⃣ 125% of the full-load current of the largest motor

3️⃣ The first 60 amperes

Whichever produces the greatest value establishes the 100% baseline.

Remember:

Greatest of the three = 100%

📉 The Next 60 Amperes

After establishing the 100% baseline:

Next 60 amperes of other loads

➡️ 50% demand factor

This means only half of that next 60-amp portion is included in the calculated load.

Quick Example

If the applicable baseline is 60 A and there is another 60 A of load:

First 60 A × 100% = 60 A

Next 60 A × 50% = 30 A

Calculated load = 90 A

⚠️ Source Note — Table Incomplete

The source material available for this Quick Hit does not include the demand-factor percentage for the final "remainder of other loads" row of Table 120.102(B).

Rather than guessing at a code value, this series leaves that portion unassigned until the complete table is available.

📌 Don't Guess the Table

When working with an actual installation, always verify the complete current edition of the NEC and applicable amendments before performing a load calculation.

🧠 Why This Matters

Farm loads can include motors, equipment, agricultural machinery, and multiple branch circuits that aren't expected to operate simultaneously.

The demand-factor table recognizes that reality.

The exam takeaway:

Find the 100% baseline first. Then apply the appropriate demand factor to the additional load tiers.

🎯 Test Yourself

Per Table 120.102(B), what demand factor applies to the next 60 amperes of load after the initial baseline tier?

A) 100%
B) 75%
C) 50%
D) 25%

✅ Answer

C) 50%

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🔎 NEC References

Primary: Article 120, 120.102(B)

Related: Table 120.102(B) — Farm Building Demand Factors

⚡ Series Progress

Article 120 — Load Calcs Won't Kill You

Part V is now underway.

Previous: Episode 38 — Welcome to the Farm
Current: Episode 39 — Farm Buildings: The 60-Amp Tiers
Next: Continue through the farm-load provisions of Article 120.