Irrigation & Lighting Division

Landscape Low Voltage Lighting

The voltage losses in the chart below were calculated using Ohm's Law, and are theoretical. Safety margin should be built into the design to take into consideration deterioration of wire splices, power brownouts, etc.
CONSULT THE MANUFACTURER OF THE LIGHT FIXTURE FOR MORE DETAIL.

NOTES: 1) Do not use a cable whose ampacity is less than the rating of the transformer circuit breaker.
  2) Chart shows voltage drop for maximum flows of 80% of the cables' ampacities.

VOLTAGE DROP PER 10 LINEAR FEET OF CABLE

LAMP POWER FLOWING IN CABLE SECTION (WATTS @ 12V) FLOW (AMPS) WIRE GAUGE (AWG), CLASS K COPPER
18 16 12 10 8
WIRE RESISTANCE (Ohms/10' of cable, both conductors) @ 77 °F (25 °C)
0.1358 0.0852 0.0336 0.0212 0.0136
20 1.67 0.226 0.142 0.056 0.035 0.023
25 2.08 0.283 0.178 0.070 0.044 0.028
30 2.50 0.340 0.213 0.084 0.053 0.034
35 2.92 0.396 0.249 0.098 0.062 0.040
40 3.33 0.453 0.284 0.112 0.071 0.045
45 3.75 0.509 0.320 0.126 0.080 0.051
50 4.17 0.566 0.355 0.140 0.088 0.057
55 4.58 0.622 0.391 0.154 0.097 0.062
60 5.00 0.679 0.426 0.168 0.106 0.068
65 5.42 0.736 0.462 0.182 0.115 0.074
70 5.83 0.792 0.497 0.196 0.124 0.079
75 6.25 0.849 0.533 0.210 0.133 0.085
80 6.67 0.905 0.568 0.224 0.141 0.091
85 7.08 0.962 0.604 0.238 0.150 0.096
90 7.50 1.019 0.639 0.252 0.159 0.102
95 7.92 1.075 0.675 0.266 0.168 0.108
100 8.33 - 0.710 0.280 0.177 0.113
105 8.75 - 0.746 0.294 0.186 0.119
110 9.17 - 0.781 0.308 0.194 0.124
115 9.58 - 0.817 0.322 0.203 0.130
120 10.00 - 0.852 0.336 0.212 0.136
125 10.42 - - 0.350 0.221 0.141
130 10.83 - - 0.364 0.230 0.147
135 11.25 - - 0.378 0.239 0.153
140 11.67 - - 0.392 0.247 0.158
145 12.08 - - 0.406 0.256 0.164
150 12.50 - - 0.420 0.265 0.170
155 12.92 - - 0.434 0.274 0.175
160 13.33 - - 0.448 0.283 0.181
165 13.75 - - 0.462 0.292 0.187
170 14.17 - - 0.476 0.300 0.192
175 14.58 - - 0.490 0.309 0.198
180 15.00 - - 0.504 0.318 0.204
185 15.42 - - 0.518 0.327 0.209
190 15.83 - - 0.532 0.336 0.215
195 16.25 - - 0.546 0.345 0.221
200 16.67 - - 0.560 0.353 0.226
205 17.08 - - 0.574 0.362 0.232
210 17.50 - - 0.588 0.371 0.238
215 17.92 - - 0.602 0.380 0.243
220 18.33 - - 0.616 0.389 0.249
225 18.75 - - 0.630 0.398 0.255
230 19.17 - - 0.644 0.406 0.260
235 19.58 - - 0.658 0.415 0.266
240 20.00 - - 0.672 0.424 0.272