Quick Hits

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

🏁 Episode 49 — Allowable Demand Factors: SERIES FINALE

Article: 120 — Load Calculations
Part: Part IX — Mobile and Manufactured Homes
Section: 120.141
Format: Quick Hit

🎯 What You'll Learn

We calculated the load for one mobile home in the last few episodes.

Now we're looking at the load calculation for an entire mobile home park.

Section 120.141 provides demand factors that account for diversity between multiple mobile homes connected to the same park wiring system.

⚠️ Source Verification Note: The final row of Table 120.141 — "61 and over" — is missing its demand-factor percentage in the source material used for this Quick Hit.

Rather than guessing the missing NEC value, it is intentionally left unidentified.

📖 The Quick Hit

🏘️ 120.141 — The Park-Wide Baseline

Park wiring is calculated at 120/240 volts using the larger of these two values:

1️⃣ 16,000 VA Per Mobile Home Lot

Start with:

➡️ 16,000 VA per mobile home lot

OR:

2️⃣ Actual 120.140 Load

Use the actual calculated load from 120.140 for the largest typical mobile home that each lot is intended to accommodate.

⚠️ Always Use the Larger Number

The calculation uses whichever is larger:

16,000 VA per lot

OR

Actual 120.140 load

The idea is to make sure the park wiring is sized for the greater of the standard baseline or the actual expected mobile-home load.

📊 Table 120.141 — The Demand Factor Curve

Once the baseline load has been established, Table 120.141 applies demand factors based on the number of mobile homes.

🏠 1 Mobile Home

➡️ 100%

No diversity discount.

🏠🏠 2 Mobile Homes

➡️ 55%

A major drop occurs once multiple homes are included.

🏘️ 5 Mobile Homes

➡️ 33%

The demand factor continues dropping as the number of homes increases.

🏘️ 10–12 Mobile Homes

➡️ 27%

🏘️ 22–40 Mobile Homes

➡️ 24%

🏘️ 41–60 Mobile Homes

➡️ 23%

🏘️ 61 and Over

➡️ Demand factor not available in the source material

⚠️ The supplied source text does not include the percentage for the "61 and over" row.

No percentage has been guessed or substituted.

📉 Why Does the Percentage Drop?

This is the same basic diversity concept we've seen throughout Article 120.

A park with one mobile home has to account for essentially the entire calculated load.

But as the number of homes increases, it becomes less likely that every home will simultaneously demand its maximum calculated load.

So the demand factor decreases as the number of homes increases.

Think:

More homes

⬇️

More diversity

⬇️

Lower percentage of the calculated total

⚠️ The Big Limitation

There's an important restriction attached to this table:

No demand factor is permitted for any other load in the park beyond what is specifically provided for by the Code.

In other words:

🚐 Mobile-home loads → Table 120.141

Other park loads → Don't automatically apply this demand factor

You can't simply take every load connected to the park and start applying the mobile-home demand factor to it.

🧠 Exam Takeaway

When you see 120.141, remember:

🏘️ Mobile home park

⚡ 120/240V

🔢 Larger of 16,000 VA per lot OR actual 120.140 load

📊 Table 120.141

📉 More homes = lower demand factor

⚠️ No demand factor for other park loads unless specifically permitted

And remember:

1 home → 100%

2 homes → 55%

5 homes → 33%

10–12 → 27%

22–40 → 24%

41–60 → 23%

61+ → source value unavailable

🎯 Test Yourself — THE FINAL QUESTION

Per Table 120.141, what demand factor applies to a mobile home park with exactly 3 mobile homes?

A) 55%

B) 44%

C) 39%

D) 33%

✅ Answer

B) 44%

A park with 3 mobile homes falls into the applicable 3–4 mobile homes range of Table 120.141, which uses a 44% demand factor.

🏆 SERIES COMPLETE

That's it.

49 Episodes. 9 Parts. One Article.

We've gone from the opening rules of Article 120 all the way through the final mobile-home-park demand factor.

⚡ Article 120 — Load Calcs Won't Kill You

✅ Part I — General rules
Voltages, rounding, floor area, noncoincident loads, PCS

✅ Part II — Branch-circuit loads
Dwellings and outlet-specific calculations

✅ Part III — Feeder & service loads
Lighting, receptacles, dryers, ranges, EVSE, neutral calculations

✅ Part IV — Optional methods
Existing dwellings, multifamily buildings, schools, restaurants

✅ Part V — Farm loads

✅ Part VI — Health care facilities

✅ Part VII — Marinas, boatyards, floating buildings & docking facilities

✅ Part VIII — RV parks

✅ Part IX — Mobile & manufactured homes

🎬 49 Episodes. 9 Parts. One Article.

From 120.1 all the way to 120.141.

That's a LOT of load calculations.

And hopefully by now...

Load calcs don't kill you. 🔌⚡

📚 Keep Exploring

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Answer the Question of the Week:
❓ www.JoshTheSparky.com/question-of-the-week

Read Sparky's Journal:
📓 www.JoshTheSparky.com/sparkys-journal

Catch the latest Sparky Weekly:
📰 www.JoshTheSparky.com/sparky-weekly

View Sources & References:
📚 www.JoshTheSparky.com/Sources

🔎 NEC References

Primary: Article 120, 120.141

Related: 120.140 — Mobile and Manufactured Homes Load Calculation

Related: Table 120.141 — Allowable Demand Factors

⚠️ Final Source Verification Note

The supplied source material does not include the demand-factor percentage for the "61 and over" row of Table 120.141.

No percentage has been guessed or substituted.

Once the complete table is available, the missing value can be added.

🏁 SERIES FINALE

Article 120 — Load Calcs Won't Kill You

Episode 49: Allowable Demand Factors

THE END. 🏆🔌⚡