Quick Hits

⚡ Quick Hit: Show Windows & Track Lighting — The Sequel

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

Episode 16

💡 THE QUICK HIT

We already looked at show windows at the branch-circuit level in 120.14(G).

Now we're looking at the feeder/service-level calculation — plus a separate rule for track lighting.

🪟 120.46(A) — Show Windows

At the feeder/service level, show-window lighting is calculated at not less than:

200 VA PER LINEAR FOOT

or

660 VA PER LINEAR METER

The measurement is taken horizontally along the base of the show window.

🔄 THE CALLBACK

That's the same basic 200 VA per linear foot figure used for the branch-circuit calculation in 120.14(G).

The difference is where the calculation is being applied:

120.14(G) → Branch-circuit level

120.46(A) → Feeder/service level

🛤️ 120.46(B) — Track Lighting

For track lighting outside dwelling units and hotel/motel guest rooms, calculate:

150 VA for every 2 feet of track

or fraction thereof.

So the calculation is based on the length of the track — not simply the number of fixtures installed on it.

⚡ MULTIPLE CIRCUITS

If the same track is supplied by multiple circuits, divide the calculated load equally among the circuits.

⚠️ THE EXCEPTION

There's an alternative when a current-limiting device supplies the track.

Instead of using the 150 VA per 2 feet calculation, the load can be based on the rating of the current-limiting device.

💡 THE IDEA

If a device is already limiting the current supplied to the track, its rating can be used as the basis for the calculation.

🎯 TEST YOURSELF

A retail store has 20 feet of track lighting with no current-limiting device.

Per 120.46(B), what is the calculated load?

A) 1,500 VA

B) 3,000 VA

C) 4,000 VA

D) 750 VA

👇 What's your answer?

🧮 SHOW YOUR MATH

Track lighting is calculated at:

150 VA per 2 feet

20 feet ÷ 2 feet:

10 sections

Then:

10 × 150 VA = 1,500 VA

⚡ CALCULATED LOAD

1,500 VA

✅ ANSWER

A) 1,500 VA

The calculation is based on 150 VA for every 2 feet of track, or fraction thereof.

🔑 REMEMBER

2 feet of track = 150 VA

20 feet = 10 × 150 VA

20 feet = 1,500 VA

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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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