Interior Lighting for Designers

TABLE 9

RECOMMENDED WIRE SIZE ANDSECONDARY WIRE LENGTH FOR LIGHTING CIRCUITS

USING 120 V PRIMARY/12 V SECONDARY TRANSFORMERS

Wire

Size

(Gauge)

Watts (VA) per Circuit

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500

Maximum Secondary Wire Length in Feet

14 75372519151211987766555444443333

12 11859393024201715131211109887776665555

10 188946347383127242119171614131312111010999888

8 299 149 100 75 60 50 43 37 33 30 27 25 23 21 20 19 18 17 16 15 14 14 13 12 12

6 476 238 159 119 95 79 68 60 53 48 43 40 37 34 32 30 28 26 25 24 23 22 21 20 19

This chart is based on SPT-3 wire and a maximum 0.63 voltage drop at the end of the run.
Exceeding the maximum secondary wire lengths noted in the chart above will cause the voltage to drop along the length of the wire.
Lamps positioned closer to the transformer will burn at a higher color temperature than those farther from it because the lamps
nearest the transformer are receiving greater voltage than those farther away.
When dimming low-voltage loads, use dimmers designed for low-voltage magnetic loads with magnetic transformers and dimmers
designed for electronic low-voltage loads with electronic transformers.
Based on the Recommended Wire Size and Voltage Drop chart from Acme Electric Corporation Catalog ATD-01.Used with
permission from the Acme Electric Corporation Power Distribution Products Division.

INTERIOR LIGHTING FOR DESIGNERS