Quick Hits

⚡ Quick Hit: Not All Lighting Gets Treated Equally — Demand Factors

Article 120 — Branch-Circuit, Feeder, and Service Load Calculations

Episode 10

💡 THE QUICK HIT

Here's a fact that can trip people up:

The more lighting load a building has, the smaller the percentage that may actually count toward the calculated demand load.

Let's look at Table 120.45 and how its demand factors work.

📖 120.45 — General Illumination Load Demand Factors

Demand factors apply to the general illumination portion of the calculated load.

⚠️ Important

These demand factors do not determine how many branch circuits are required.

They affect the calculated feeder/service load.

Think of it as a demand calculation adjustment — not a reduction in the actual connected lighting load.

🏠 DWELLING UNITS

Table 120.45 applies the following demand factors:

General Lighting Load

Demand Factor

First 3,000 VA

100%

3,001–120,000 VA

35%

Over 120,000 VA

25%

💡 The Idea

As the calculated lighting load increases, the demand factor applied to the additional load decreases.

The entire connected lighting load isn't assumed to be operating at its maximum demand simultaneously.

🏨 HOTELS & MOTELS

For hotels and motels without tenant cooking, Table 120.45 provides:

General Lighting Load

Demand Factor

First 20,000 VA or less

60%

20,001–100,000 VA

50%

Over 100,000 VA

35%

📦 WAREHOUSES

For warehouse storage areas:

General Lighting Load

Demand Factor

First 12,500 VA or less

100%

Over 12,500 VA

50%

🏢 EVERYTHING ELSE

If the occupancy isn't one of the categories specifically addressed by Table 120.45:

100%

No demand-factor reduction is provided by this table.

⚠️ THE HOTEL/MOTEL FOOTNOTE

Here's the part that's easy to miss.

The hotel/motel demand factors of:

60% → 50% → 35%

do not apply to feeders or services supplying areas where the entire lighting load is likely to be used simultaneously.

🎉 Think Ballrooms & Dining Rooms

If an entire ballroom is being used for a wedding reception and all of the lighting is expected to operate at once, applying a demand-factor "discount" wouldn't make sense.

The lighting demand is actually expected to be there.

🎯 TEST YOURSELF

A dwelling unit has a calculated general lighting load of 5,000 VA.

According to Table 120.45, what demand factor applies to the portion from 3,001–5,000 VA?

A) 100%

B) 60%

C) 35%

D) 25%

👇 What's your answer?

✅ ANSWER

C) 35%

The first 3,000 VA is subject to the 100% demand factor.

The portion from 3,001 through 5,000 VA falls within the next range and is subject to the 35% demand factor.

🧮 BONUS

For the 5,000 VA example:

First 3,000 VA × 100% = 3,000 VA

Remaining 2,000 VA × 35% = 700 VA

Total calculated demand = 3,700 VA

📚 KEEP EXPLORING

More from Article 120

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→ Understanding Load Calculations

→ What Are Noncoincident Loads?

→ How PCS Changes Load Calculations

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⚠️ EDUCATIONAL NOTICE

This Quick Hit is an educational explanation based on the author's understanding of the NEC. It is not a substitute for the official NEC, applicable local amendments, manufacturer instructions, or the determination of the Authority Having Jurisdiction (AHJ).

Always verify the requirements applicable to your specific installation.

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