Quick Hits

⚡ Quick Hit: Who Gets to Use the Dwelling Shortcut?

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

Episode 26 — 120.82(A) Dwelling Unit Optional Calculation

🏠 THE DWELLING UNIT SHORTCUT

We just entered Part IV — Optional Calculations.

Now we're getting into one of the most useful optional methods in Article 120:

120.82 — Dwelling Unit

But before you start adding up loads, there's a very important question:

DO YOU QUALIFY?

Because this method isn't available for every dwelling.

✅ 120.82(A) — THE ELIGIBILITY CHECK

To use this optional calculation method, the installation must meet all three of these conditions:

1️⃣ SINGLE DWELLING UNIT

The optional method applies to a single dwelling unit.

2️⃣ ONE SERVICE OR FEEDER

The entire dwelling unit is supplied by one:

120/240-volt, 3-wire

or

208Y/120-volt, 3-wire

service or feeder.

3️⃣ 100 AMPS OR MORE

That service or feeder must have a rating of at least:

100 AMPS

🚦 THE THREE-QUESTION TEST

Before using 120.82, ask:

🏠 Is it a single dwelling unit?

YES / NO

⚡ Is it supplied by one qualifying service or feeder?

YES / NO

🔌 Is that service or feeder rated 100A or more?

YES / NO

✅ ALL THREE =

120.82 may be available

❌ ANY ONE NO =

You're looking at the standard calculation method instead.

🧮 SO WHAT HAPPENS IF YOU QUALIFY?

Once you've passed the eligibility check, 120.82 breaks the optional calculation into three major load buckets:

🅱️ GENERAL LOADS

General loads covered by 120.82(B).

↓

🅲 HEATING & AIR-CONDITIONING LOAD

Covered by 120.82(C).

↓

🅳 EVSE LOADS

Covered by 120.82(D).

➕

Those three buckets are combined to determine the calculated load.

⚪ WHAT ABOUT THE NEUTRAL?

Remember our Part III finale?

The neutral calculation is still handled under:

120.61

So don't assume the optional method means you throw away everything you've already learned.

Part IV gives you an optional load-calculation method.

It doesn't erase the other applicable requirements.

🧠 THE BIG IDEA

120.82 starts with eligibility.

Don't jump straight into the math.

First determine:

Does this dwelling qualify?

Then:

Calculate the three applicable load buckets.

🎯 TEST YOURSELF

Per 120.82(A), what is the minimum ampacity a dwelling's service or feeder must have to qualify for this optional method?

A) 60 amps

B) 100 amps

C) 200 amps

D) There is no minimum

👇 What's your answer?

✅ ANSWER

B) 100 AMPS

The dwelling-unit optional calculation method in 120.82(A) requires the qualifying service or feeder to be rated at least 100 amperes.

🔑 REMEMBER:

100A = THE GATE

But amperage alone isn't enough.

You also need the qualifying:

🏠 Single dwelling unit

⚡ One service or feeder

🔌 100A or greater

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🧭 QUICK HIT NAVIGATION

← Back to Article 120 Quick Hits

← Episode 25 — Welcome to Part IV

→ Episode 27 — 120.82(B) General Loads

🏠 120.82 SERIES

Episode 26: Who Gets to Use This Shortcut?

Episode 27: General Loads

Episode 28: Heating & Air-Conditioning

Episode 29: EVSE Loads

Episode 30: Putting the Optional Method Together

⚠️ 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.