Quick Hits

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

⛵ Episode 43 — Marinas: Shore Power Gets Its Own Discount Curve

Article: 120 — Load Calculations
Part: Part VII — Marinas, Boatyards, Floating Buildings & Docking Facilities
Section: 120.120
Format: Quick Hit

🎯 What You'll Learn

Marinas, boatyards, floating buildings, and docking facilities have their own demand-factor rules for shore-power receptacles.

Section 120.120 provides a specific method for calculating the load of receptacles supplying boats — including several important notes that can change how the load is calculated.

📖 The Quick Hit

⛵ Shore-Power Receptacles

General lighting and other loads at marinas, boatyards, floating buildings, and docking facilities continue to be calculated using the standard Part III methods.

However, receptacles supplying shore power to boats can use the demand factors in Table 120.120.

⚠️ Important: When Table 120.120 is used, the 120.61(B) neutral-load reduction cannot also be applied.

You don't get to stack both demand-factor methods on top of each other.

📊 Table 120.120 Demand Factors

The table provides different demand factors based on the number of shore-power receptacles.

1–4 receptacles

➡️ 100%

9–14 receptacles

➡️ 80%

15–30 receptacles

➡️ 70%

41–50 receptacles

➡️ 50%

71 or more receptacles

➡️ 30%

The basic idea is diversity.

As the number of shore-power receptacles increases, the percentage of the calculated load that must be included decreases because it is unlikely that every boat will simultaneously operate at its maximum calculated load.

📝 The Three Notes

1️⃣ Multiple Shore-Power Receptacles at One Slip

If a slip has two shore-power receptacles with different voltage or ampere ratings, only the receptacle with the greater kW demand is included.

In other words, don't automatically add both receptacles together when the rule directs you to use the greater kW demand.

2️⃣ Individual kWh Submeters

If each slip's shore-power pedestal is equipped with an individual kWh submeter, the final demand amperes are multiplied by:

➡️ 0.9

That's a 10% reduction to the resulting demand amperes.

3️⃣ Boat Hoist + Shore Power

If the same circuit supplies both a boat hoist and shore power at a slip, only the load with the greater kW demand is included.

Again, the rule prevents you from simply adding both loads together when the larger-load method applies.

🧠 Exam Takeaway

When you see 120.120, think:

⛵ Marina / boatyard / floating building / docking facility

🔌 Shore-power receptacles

📊 Table 120.120

⚡ More receptacles = lower demand factor

🚫 Don't combine Table 120.120 with the 120.61(B) neutral reduction

And remember the special notes:

Two receptacles at one slip? → Use the greater kW demand.

Individual kWh submeter? → Multiply final demand amperes by 0.9.

Boat hoist + shore power? → Use the greater kW demand.

🎯 Test Yourself

Per Table 120.120, what demand factor applies to a marina with 20 shore-power receptacles?

A) 100%
B) 90%
C) 70%
D) 60%

✅ Answer

C) 70%

A marina with 20 shore-power receptacles falls within the 15–30 receptacle range of Table 120.120.

Therefore, the applicable demand factor is:

70%

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🔎 NEC References

Primary: Article 120, 120.120

Related: Table 120.120 — Shore-Power Receptacle Demand Factors
Related: 120.61(B) — Neutral Load Calculation

⚡ Series Progress

Article 120 — Load Calcs Won't Kill You

⛵ Part VII — Marinas, Boatyards, Floating Buildings & Docking Facilities

Episode 41: Hospital Receptacles Get Their Own Discount Table
Episode 42: Patient Care Circuits Get Their Own Rule Too
Episode 43: Marinas: Shore Power Gets Its Own Discount Curve

➡️ Next Up

The series continues through Part VII — Marinas, Boatyards, Floating Buildings & Docking Facilities.

Next section: 120.121 and beyond.