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🎬 NEC 2026 ARTICLE 120 SERIES
PART 2 OF 30 — NEC 120.5 | CALCULATION RULES

NEC 2026 ARTICLE 120.5 EXPLAINED ⚡
THE RULES BEHIND EVERY LOAD CALCULATION
joshthesparky4 · Josh The Sparky

⚡ OPENING HOOK

Before you start calculating...

You need to know the rules. ⚠️

Because every load calculation in the NEC starts from the same foundation.

🧠 CORE IDEA

⚡ NEC 120.5 establishes the basic rules used for all load calculations in Article 120.

It defines how electricians must approach:

⚡ System voltages
📏 Floor area measurements
🔢 Rounding rules
🔋 DC load treatment

These rules ensure consistency across every calculation method in the NEC.

🧠 CODE CONNECTION

⚡ NOMINAL VOLTAGES

Unless otherwise specified, calculations must use standard system voltages such as:

• 120V
• 120/240V
• 208Y/120V
• 240V
• 277/480V
• 347/600V
• 600V

⚡ Always use nominal system voltage—not measured field voltage.

📏 FLOOR AREA RULES

Dwelling unit calculations are based on outside building dimensions.

DO NOT INCLUDE:

❌ Detached garages
❌ Open porches
❌ Unfinished areas not intended for future living space

🔢 ROUNDING RULES

⚡ Fractional values under 0.5A may be rounded down to the nearest whole amp.

🧠 CORE TAKEAWAY

⚡ Every load calculation starts with the same baseline rules.

⚡ Voltage, area, and rounding rules control the accuracy of every result.

⚡ Getting this wrong affects every downstream calculation.

⚡ FINAL LINE

Before you calculate anything...

Make sure you're using the right rules. ⚡

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