Quick Hits

⚡ Quick Hit: The Multifamily Demand Factor Table

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

Episode 33 — 120.84(C) Multifamily Dwelling Unit Demand Factors

🏢 MORE UNITS = MORE DIVERSITY

In Episode 32, we answered the first question:

Who qualifies for the multifamily optional method?

Now comes the payoff.

Once a multifamily building qualifies, Table 120.84(C) applies a demand factor to the calculated load of the dwelling units.

And there's a pattern worth remembering:

📉 MORE UNITS → LOWER DEMAND FACTOR

Why?

The calculation recognizes that it's unlikely every dwelling unit will operate all of its electrical loads at maximum demand at exactly the same time.

More units create more diversity.

🧮 WHAT GOES INTO EACH UNIT'S LOAD?

Before applying the table's demand factor, you first determine the applicable calculated load for the dwelling units.

That includes:

1️⃣ GENERAL LIGHTING + RECEPTACLES

2 VA per square foot

2️⃣ SMALL-APPLIANCE + LAUNDRY CIRCUITS

1,500 VA for each applicable circuit.

3️⃣ APPLIANCE LOADS

Include the applicable nameplate ratings of:

🔌 Fastened-in-place appliances

🍳 Ranges / ovens / cooktops

👕 Dryers not supplied by laundry circuits

🔥 Water heaters

4️⃣ OTHER PERMANENTLY CONNECTED MOTORS

Include the applicable nameplate rating of permanently connected motors not already included elsewhere.

5️⃣ HEATING / AC

Use the:

LARGER OF THE AC LOAD OR SPACE-HEATING LOAD

Not both.

📊 TABLE 120.84(C)

Now we apply the multifamily demand factor.

Here are some points along the curve:

Number of Dwelling Units

Demand Factor

3–5

45%

8–10

43%

18–20

38%

28–30

33%

43–45

27%

56–61

24%

62 and over

23%

📉 See the pattern?

As the number of dwelling units increases:

45% → 43% → 38% → 33% → 27% → 24% → 23%

The calculated demand factor gets smaller.

🏙️ THE BOTTOM OF THE CURVE

What happens when the building gets REALLY big?

62 dwelling units and over

The table reaches:

23%

That's the lowest demand factor in this table.

The diversity factor doesn't continue dropping forever.

62+ units = 23%

🧠 WHY DOES THE PERCENTAGE DROP?

Think about two buildings.

🏠 BUILDING A

3 dwelling units

There's a greater chance that a large portion of the units' electrical loads could be operating at the same time.

🏢 BUILDING B

100 dwelling units

It's much less likely that every unit will simultaneously reach its calculated maximum demand.

That's the basic concept behind:

DIVERSITY

More dwelling units → greater diversity → lower calculated percentage.

🎯 TEST YOURSELF

Per Table 120.84(C), what demand factor applies to a multifamily building with exactly 12 dwelling units?

A) 45%

B) 41%

C) 38%

D) 33%

👇 What's your answer?

✅ ANSWER

B) 41%

A multifamily building with 12 dwelling units falls into the applicable table range for a 41% demand factor.

🔑 REMEMBER:

Don't just memorize the biggest and smallest numbers.

The table works across ranges of dwelling-unit counts.

📋 THE BIG PICTURE

STEP 1

Determine the calculated load for the dwelling units.

⬇️

STEP 2

Determine the number of dwelling units.

⬇️

STEP 3

Find the applicable demand factor in Table 120.84(C).

⬇️

STEP 4

Apply the factor to the applicable dwelling-unit load.

⚡ That's the basic flow.

🏢 120.84 — WHAT WE KNOW NOW

Episode 32

🚦 QUALIFICATION

Three or more dwelling units, plus the applicable qualification conditions.

Episode 33

📊 DEMAND FACTOR

Use Table 120.84(C).

The overall pattern:

MORE UNITS = LOWER FACTOR

🔜 NEXT: 120.85

We've covered:

🏠 Single dwelling units

🏚️ Existing dwelling units

🏢 Multifamily dwelling units

Next, Article 120 moves into another specific dwelling-unit arrangement:

120.85 — Two Dwelling Units

A shorter section, but worth keeping in the series because it's another example of the NEC creating a calculation method for a specific situation.

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🧭 QUICK HIT NAVIGATION

← Back to Article 120 Quick Hits

← Episode 32 — Multifamily Buildings: The 3-Condition Checklist

→ Episode 34 — 120.85 Two Dwelling Units

🏠 ARTICLE 120 — PART IV

Episode 25: Welcome to Part IV

Episode 26: Who Gets to Use This Shortcut?

Episode 27: Bucket #1 — General Loads

Episode 28: Bucket #2 — Heating & AC (Part 1)

Episode 29: Bucket #2 — Heating & AC (Part 2)

Episode 30: Bucket #3 — EVSE + Putting It All Together

Episode 31: Existing Dwelling Units

Episode 32: Multifamily Dwelling Units

Episode 33: Multifamily Demand Factor Table ← YOU ARE HERE

Episode 34: Two Dwelling Units

⚠️ 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.

The National Electrical Code® and NEC® are registered trademarks of NFPA. JoshTheSparky.com is not affiliated with, sponsored by, or endorsed by NFPA.