Quick Hits

⚡ Quick Hit: Space Heaters — No Discounts Allowed

Article 120 — Branch-Circuit, Feeder, and Service Load Calculations

Episode 11

🔥 THE QUICK HIT

Most loads in Article 120 can involve some form of demand factor.

Fixed electric space heating is different.

Under 120.51, fixed electric space-heating loads are generally calculated at 100% of the total connected load.

No demand-factor reduction.

📖 120.51 — Fixed Electric Space Heating

🔥 100% OF THE CONNECTED LOAD

Fixed electric space-heating loads are calculated at:

100%

of the total connected load.

That means you don't simply apply a demand-factor reduction because you expect every heating unit won't necessarily operate at the same time.

⚠️ FEEDER/SERVICE FLOOR

The feeder or service supplying the heating equipment also cannot be rated less than the largest branch circuit it supplies, regardless of the calculated demand.

⚡ THE EXCEPTION

There is an important exception.

If the heating units operate:

• Intermittently

• On a duty cycle

• Or in a manner where the units will never all operate simultaneously

the Authority Having Jurisdiction (AHJ) may approve a lower conductor ampacity than would otherwise be required based on 100% of the connected load.

🚨 Important Distinction

This isn't an automatic demand factor.

The AHJ must approve it.

So don't assume that intermittent operation automatically gives you permission to reduce the calculated load.

🎯 TEST YOURSELF

Per 120.51, what percentage of the total connected load must fixed electric space heating be calculated at, absent an AHJ-approved exception?

A) 125%

B) 80%

C) 100%

D) 75%

👇 What's your answer?

✅ ANSWER

C) 100%

Absent an AHJ-approved exception, fixed electric space-heating loads are calculated at 100% of the total connected load.

📚 KEEP EXPLORING

More from Article 120

← Back to Article 120 Quick Hits

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→ Understanding Load Calculations

→ Not All Lighting Gets Treated Equally: Demand Factors

→ What Are Noncoincident Loads?

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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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