Can I keep 14 AWG if the lights draw less than 15 amps?

Type the actual load. Drop is proportional to current. A circuit loaded to 8 A loses less voltage than the same wire at 15 A.

What does the red or amber badge mean?

Green is 3 percent or less, amber is between 3 and 5 percent, and red is above 5 percent.

Is the loss number the lamp wattage?

No. It is I²R heating in the conductors, not the power used by the lights.

15 Amp Lighting Run Voltage Drop at 100 Feet

A 100 ft, 120 V lighting circuit at 15 A and a 3 percent limit.

Formula SSC-2026.1

K method · SSC-2026.1

Minimum size

8 AWG · 8.37 mm²

Single conductor set

Voltage drop

2.34 V

1.95% · end 117.7 V

Power loss

35 W

I²R at the operating current

Required ampacity

15.0 A

Each conductor 50 A

Material estimate

$588.00

3 conductors + EMT

Conductor weight

19.2 lb

8.7 kg · approximate insulated weight

Single-line and conductor gaugeLive scaled blueprint

Circle diameters track circular mils. The drawing is a schematic, not a conduit-fill layout.

Bill of materials and shopping list
Item	Net	Waste	Order	Unit price	Line total
copper 8 AWG · 8.37 mm²	100 ft one way	cuts excluded	3 conductors	USD	$403.00
EMT conduit	100 ft	—	100 ft	USD	$185.00

Copper versus aluminum at this run
Material	Minimum size	mm²	Drop	End voltage	Loss
copper	8 AWG · 8.37 mm²	8.4	1.95%	117.7 V	35 W
aluminum	6 AWG · 13.3 mm²	13.3	2.02%	117.6 V	36 W

Same load at other one-way distances
Distance	Minimum size	Drop	Percent	End voltage
50 ft	12 AWG · 3.31 mm²	2.96 V	2.47%	117.0 V
75 ft	10 AWG · 5.26 mm²	2.80 V	2.33%	117.2 V
100 ft	8 AWG · 8.37 mm²	2.34 V	1.95%	117.7 V
150 ft	8 AWG · 8.37 mm²	3.52 V	2.93%	116.5 V

Show the deterministic formula

Single phase: Vdrop = 2 × K × I × D / cmil. Three phase: Vdrop = 1.732 × K × I × D / cmil. K is 12.9 for copper and 21.2 for aluminum. D is one-way feet.

Percent drop = Vdrop ÷ source voltage × 100. Green is 3% or less, amber is 3 to 5%, and red is over 5%. Power loss is I²R on the current-carrying conductors.

The smallest conductor that meets both the ampacity (125% when continuous) and the drop limit is selected. Ampacity does not include bundling or temperature correction.

Contractor sign-off

Project: 15 Amp Lighting Run Voltage Drop at 100 Feet

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Date

Verified by (PE / electrician / inspector)

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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.

Engineering notes

Fourteen AWG copper is limited to 15 A, so it passes ampacity for this circuit and then fails the drop. At 100 ft and 120 V the calculator steps through 12 and 10 AWG until the drop is inside 3 percent. That is the point of the page: breaker size and wire size are different questions on a long lighting homerun. The load is modeled at the full 15 A even if the lamps draw less. Lower the amps if you know the actual load.

Code reference

NEC 210.19(A) and 215.2(A) informational notes recommend 3 percent on a branch circuit and 5 percent total with the feeder. Ampacity follows the 75°C column of Table 310.16 plus the small-conductor limits. Confirm the adopted edition.

Field questions

Can I keep 14 AWG if the lights draw less than 15 amps?: Type the actual load. Drop is proportional to current. A circuit loaded to 8 A loses less voltage than the same wire at 15 A.
What does the red or amber badge mean?: Green is 3 percent or less, amber is between 3 and 5 percent, and red is above 5 percent.
Is the loss number the lamp wattage?: No. It is I²R heating in the conductors, not the power used by the lights.