Quick Hits

⚡ Quick Hit: Electric Clothes Dryers — Dwelling Units

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

Episode 17 — 120.54 Electric Clothes Dryers — Dwelling Unit(s)

👕 THE QUICK HIT

We already saw the familiar 5,000 VA dryer rule back in 120.14(B) at the branch-circuit level.

Now we're moving to the feeder/service level.

The basic load value stays familiar — but 120.54 adds demand-factor provisions and a special 3-phase calculation rule.

🔌 120.54 — Electric Clothes Dryers

For each electric clothes dryer in a dwelling unit:

Nameplate Rating OR 5,000 VA — WHICHEVER IS LARGER

That means a dryer with a nameplate rating below 5,000 VA is still calculated at 5,000 VA.

A dryer with a nameplate rating above 5,000 VA uses its actual nameplate rating.

💡 QUICK EXAMPLES

4,200 W nameplate

→ 5,000 VA calculated load

5,000 W nameplate

→ 5,000 VA calculated load

5,800 W nameplate

→ 5,800 VA calculated load

📊 TABLE 120.54 — DEMAND FACTORS

Here's where the feeder/service calculation gets different.

Table 120.54 permits demand factors to be applied to electric clothes dryer loads.

That's especially useful when a feeder or service supplies multiple dwelling units with multiple dryers.

⚠️ IMPORTANT

The demand-factor table doesn't mean every dryer automatically gets calculated at the same reduced percentage.

Use the applicable provisions of Table 120.54 for the number of dryers being supplied.

⚡ THE 3-PHASE CURVEBALL

There's a special rule when:

• There are two or more single-phase dryers

• They're supplied by a 3-phase, 4-wire feeder or service

Instead of simply adding every dryer together, the calculated load is based on:

2 × the maximum number of dryers connected between any two phases

🧠 WHY THIS MATTERS

The way the dryers are distributed across the three phases matters.

This isn't simply:

Dryer 1 + Dryer 2 + Dryer 3 + Dryer 4...

You have to look at the phase-to-phase distribution and identify the maximum number connected between any two phases.

🔑 REMEMBER

3-phase, 4-wire + 2 or more single-phase dryers

↓

Find the maximum number between any two phases

↓

Multiply that number by 2

🎯 TEST YOURSELF

A dwelling-unit electric dryer has a nameplate rating of:

4,200 W

Per 120.54, what VA value must be used for the load calculation before applying any permitted demand factor?

A) 4,200 VA

B) 5,000 VA

C) 4,600 VA

D) 0 VA — nameplate always wins regardless of size

👇 What's your answer?

🧮 SHOW YOUR MATH

Nameplate rating:

4,200 W

Minimum calculation value:

5,000 VA

Compare the two:

4,200 < 5,000

Therefore:

⚡ Calculated load = 5,000 VA

✅ ANSWER

B) 5,000 VA

The dryer is calculated using the larger of the nameplate rating or 5,000 VA.

🔥 THE TAKEAWAY

Under 5,000 VA? → Use 5,000 VA

Over 5,000 VA? → Use the nameplate rating

Then check whether a Table 120.54 demand factor applies to the overall dryer load.

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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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