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 count toward the calculated demand load.

Let's break down Table 120.45.

📖 120.45 — General Illumination Demand Factors

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

⚠️ IMPORTANT

These demand factors do not change the number of branch circuits required.

They affect the calculated feeder/service load.

Think of it this way:

Connected lighting load ≠ calculated demand load

🏠 DWELLING UNITS

Table 120.45 provides these 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 operate at maximum demand simultaneously.

🏨 HOTELS & MOTELS

For hotels and motels without tenant cooking:

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%

🏢 ALL OTHER OCCUPANCIES

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

100%

No demand-factor reduction is provided by Table 120.45.

⚠️ THE HOTEL/MOTEL GOTCHA

There's an important exception to the hotel/motel demand factors.

The 60% / 50% / 35% factors don't apply to feeders or services supplying areas where the entire lighting load is likely to be used simultaneously.

🎉 THINK BALLROOMS & DINING ROOMS

A ballroom during a wedding reception is a good example.

If the lighting is expected to operate all at once, applying a demand-factor reduction wouldn't accurately represent the expected load.

🔑 REMEMBER

Not every area of a hotel gets the hotel/motel demand factor.

Look at how the area is actually expected to be used.

🎯 TEST YOURSELF

A dwelling unit has a calculated general lighting load of:

5,000 VA

Per 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?

🧮 BONUS — SHOW YOUR MATH

The first 3,000 VA is calculated at 100%:

3,000 VA × 100% = 3,000 VA

The remaining load is:

5,000 − 3,000 = 2,000 VA

That portion falls within the 3,001–120,000 VA range:

2,000 VA × 35% = 700 VA

TOTAL DEMAND LOAD

3,000 + 700 = 3,700 VA

✅ ANSWER

C) 35%

The portion from 3,001 through 5,000 VA falls within the 35% demand-factor range.

⚡ FINAL RESULT

5,000 VA connected lighting load

↓

3,700 VA calculated demand load

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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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