Quick Hits

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

🌾 Episode 40 — Combining Every Farm Building Into ONE Total Load

Article: 120 — Load Calculations
Part: Part V — Farm Loads
Section: 120.103
Format: Quick Hit

🎯 What You'll Learn

Once each farm building has been calculated individually, you aren't finished.

When multiple farm buildings share a common service, Section 120.103 provides the method for combining those individual building loads into one service-level load.

The big idea:

Calculate each building → rank the loads → apply the demand factors → add the dwelling load.

📖 The Quick Hit

🌾 From Individual Buildings to One Farm Load

When a common service supplies the entire farm, the total calculated load consists of:

🏠 Dwelling unit load
➕ Combined farm-building loads

The dwelling portion is calculated using the applicable Part III or Part IV method.

The individual farm-building loads are calculated using Table 120.102(B) and then combined using Table 120.103.

🔗 Buildings With the Same Function

There's an important detail before applying the demand factors.

Equipment located in two or more buildings that performs the same function can be combined into a single line item.

Think of it this way:

Same function across multiple buildings → combine first → then apply the table.

This can change the size of the load that enters the demand-factor calculation.

📊 Table 120.103 — Rank the Buildings

Once the individual farm-building loads have been established, rank them from largest to smallest.

Then apply the demand factors:

Rank

Demand Factor

🥇 Largest

100%

🥈 Second largest

75%

🥉 Third largest

65%

Remaining loads

50%

The Shortcut to Remember

100% → 75% → 65% → 50%

The farther down the list you go, the smaller the percentage applied to the load.

🧮 Quick Example

Suppose a farm has four calculated building loads:

• Building #1 → 100 A

• Building #2 → 80 A

• Building #3 → 60 A

• Building #4 → 40 A

Apply Table 120.103:

100 A × 100% = 100 A

80 A × 75% = 60 A

60 A × 65% = 39 A

40 A × 50% = 20 A

Combined farm-building load = 219 A

The dwelling load is then accounted for separately as required by the section.

⚠️ Don't Forget the Dwelling

The farm-building demand calculation isn't the entire farm service calculation.

When the common service supplies the dwelling and the farm buildings:

Dwelling load + calculated farm-building load = overall service load

That's an important distinction.

🧠 Why This Matters

A farm may have multiple buildings with equipment that operates at different times.

Rather than assuming every building operates at its full calculated load simultaneously, Table 120.103 provides a tiered demand-factor approach.

Exam Memory Trick:

Rank the buildings first. Then apply the percentages.

Don't apply 100%, 75%, 65%, and 50% based on the order the buildings were encountered.

Largest gets 100%.
Second gets 75%.
Third gets 65%.
Everything remaining gets 50%.

🎯 Test Yourself

Per Table 120.103, what demand factor applies to the THIRD largest individual farm-building load?

A) 100%
B) 75%
C) 65%
D) 50%

✅ Answer

C) 65%

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🔎 NEC References

Primary: Article 120, 120.103

Related: Table 120.102(B) — Individual Farm Building Loads
Related: Table 120.103 — Farm Service Demand Factors
Related: 120.102(A) — Farm Dwelling Load

⚡ Series Progress

Article 120 — Load Calcs Won't Kill You

🌾 Part V — Farm Loads

Episode 38: Welcome to the Farm
Episode 39: Farm Buildings: The 60-Amp Tiers
Episode 40: Combining Every Farm Building Into ONE Total Load

The farm-load calculation now moves from individual buildings → the common farm service.