Quick Hits

⚡ Quick Hit: Multifamily Buildings — The 3-Condition Checklist

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

Episode 32 — 120.84 Multifamily Dwelling Units

🏢 THE MULTIFAMILY SHORTCUT

We've already seen optional methods for:

🏠 Single dwelling units

🏚️ Existing dwelling units

Now we're moving to:

🏢 MULTIFAMILY DWELLINGS

If you're dealing with a building containing 3 or more dwelling units, 120.84 provides another optional calculation method.

But there's a catch.

🚦 THREE CONDITIONS MUST BE MET

You don't get to use the shortcut just because it's an apartment building.

You've got to clear all three hoops.

1️⃣ ONE FEEDER PER DWELLING UNIT

No dwelling unit can be supplied by more than one feeder.

If a dwelling unit is supplied by multiple feeders, the qualification requirement isn't met.

Think:

🏠 UNIT → ONE FEEDER

for purposes of this qualification.

2️⃣ ELECTRIC COOKING

Every dwelling unit must have electric cooking equipment.

🍳 Ranges

🔥 Electric ovens

⚡ Electric cooktops

The requirement is about the dwelling units having electric cooking equipment.

3️⃣ ELECTRIC HEATING / AC

Every dwelling unit must have:

🌡️ Electric space heating

OR

❄️ Air-conditioning

OR

🌡️❄️ Both

🧠 THE 3-HOOP TEST

Before using the optional multifamily calculation, ask:

✅ 1. One feeder per dwelling unit?

✅ 2. Electric cooking in every unit?

✅ 3. Electric space heating, AC, or both in every unit?

ALL THREE = QUALIFICATION

Miss one?

🚫 Don't use the shortcut.

🍳 THE ELECTRIC-COOKING EXCEPTION

There's an important provision for buildings without electric cooking equipment.

Under the specified conditions, if the standard Part III calculation produces a higher result than the optional method plus the applicable cooking allowance, the permitted calculation can use the lower result.

⚠️ Don't confuse this with the basic three-condition qualification test.

It's a specific provision — not a blanket rule saying every multifamily building without electric cooking automatically qualifies.

⚡ THE 3-PHASE TWIST

Yep.

We've seen this pattern before.

Dryers.

Cooking appliances.

Now multifamily dwelling units.

When the applicable single-phase dwelling units are supplied from a:

3-phase, 4-wire, 120/208V system

the calculation uses the maximum number of units connected between any two phases.

The total demand is:

2 × the maximum number connected between any two phases

🧮 WHY PHASE DISTRIBUTION MATTERS

You can't always just:

Add every dwelling unit together.

The way those units are distributed across the phases matters.

Think:

Find the largest two-phase combination

⬇️

Multiply that number by 2

That's the special calculation approach described here.

🏠 WHAT ABOUT THE HOUSE LOADS?

Here's another important distinction.

An apartment building doesn't only have dwelling units.

There may also be:

💡 Hallway lighting

🛗 Elevators

🔌 Common-area receptacles

🧺 Laundry facilities

🏢 Other house/common loads

These are not simply thrown into the per-dwelling-unit shortcut.

House loads are calculated separately.

They follow the applicable standard Part III load-calculation method.

🎯 TEST YOURSELF

Per 120.84(A)(1), which of these is REQUIRED for a multifamily building to qualify for the Table 120.84(C) optional calculation?

A) Each dwelling unit has electric cooking equipment

B) At least one unit shares a feeder with another

C) No units have space heating or AC

D) The building must have fewer than 3 units

👇 What's your answer?

✅ ANSWER

A) Each dwelling unit has electric cooking equipment

Electric cooking equipment in every dwelling unit is one of the conditions for using the optional multifamily calculation method.

🔑 REMEMBER THE THREE:

ONE FEEDER

➕

ELECTRIC COOKING

➕

ELECTRIC HEAT / AC

= CHECK THE QUALIFICATION

📋 120.84 QUICK REFERENCE

Requirement

Required?

3+ dwelling units

✅

One feeder per dwelling unit

✅

Electric cooking in every unit

✅

Electric space heating, AC, or both in every unit

✅

House/common loads included in per-unit shortcut

❌

House/common loads calculated separately

✅

🧠 120.82 → 120.83 → 120.84

Notice how Part IV is building a progression:

🏠 120.82

Single dwelling unit

🏚️ 120.83

Existing dwelling unit

🏢 120.84

Multifamily dwelling units

Different situations.

Different optional methods.

Same overall goal:

⚡ Calculate the load without automatically using the standard method.

🔜 NEXT: TABLE 120.84(C)

Episode 32 established who qualifies.

Next we get into:

📊 How the multifamily demand factors actually work.

That's where Table 120.84(C) becomes the star of the show.

📚 KEEP EXPLORING

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🧭 QUICK HIT NAVIGATION

← Back to Article 120 Quick Hits

← Episode 31 — Existing Dwelling Units

→ Episode 33 — Table 120.84(C): Multifamily Demand Factors

🏠 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 ← YOU ARE HERE

Episode 33: Table 120.84(C)

⚠️ 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.