Length of 2-Wire 70V line Cable Selection
by: John Vellone
The following will help you determine the correct cable for you 70 volt installation. Yes, size does matter! Every install is similar but different. Make sure you use the correct cable gauge in order to deliver maximum power to your speakers. The correct cable will ensure you not only deliver sufficient power, but will ensure maximum frequency response and dynamic range of your sound. This will ensure that you have excellent music reproduction and voice intelligibility.
Stranded Wire: It is recommended to use stranded wire with the most number of strands available. Since electrons travel easier and faster on the perimeter of an atom hence on the perimeter of a cable strand, more finer strands will give you better frequency response.
Largest Gauge: The larger the gauge of your wire the further the distance you can run. Also a higher gauge will ensure better current flow thus delivering the maximum available power. P=V*I {Power (P) = Volts (V) multiplies by current (I)}.
Twisted Cable: A transformer driven or bridged output driven amplifier actually delivers a positive and a negative signal phase, thus a 70V output can be considered as balanced signal. A two conductor twisted cable will eliminate interference both outwards (from the Cable) and inwards ( into the cable).
Shielding / Conduits: When runned into metal electrical conduit, make sure the conduit is grounded, this will offer additional shielding and insure that the 70V system signal will not cross talk with other signals such as other 70V systems, fire evacuation systems, intercom, telecom or Data signals
This table will help you determine the maximum cable length to run in a 70 volt installation using the minimum cable gauge size.
Length of 2-Wire 70V line vs Delivering Power at .5dB (12.5%) Loss
| Wire Size AWG | Resistance per 1000ft | Maximum safe Current | Maximum safe Power | Nominal Power in The Load | |||||||||
| 10W | 15W | 20W | 30W | 40W | 60W | 100W | 200W | 400W | 1000w | ||||
| 6 | 0.8 | 50 | 3500 |
*(1) |
*(1) | *(1) | *(1) | 9100 | 6200 | 3640 | 1820 | 910 | 360 |
| 8 | 1.28 | 35 | 2450 |
*(2) |
*(2) | *(2) | 7800 | 5700 | 3900 | 2280 | 1140 | 570 | 230 |
| 10 | 2.0 | 25 | 1750 |
*(3) |
9900 | 7300 | 5000 | 3700 | 2500 | 1450 | 730 | 370 | 150 |
| 12 | 3.2 | 20 | 1400 | 9100 | 6200 | 4600 | 3100 | 2300 | 1600 | 910 | 460 | 230 | 90 |
| 14 | 5.2 | 15 | 1000 | 5600 | 3800 | 2800 | 1900 | 1400 | 950 | 560 | 280 | 140 | 56 |
| 16 | 8.0 | 6 | 420 | 3600 | 2400 | 1800 | 1200 | 900 | 600 | 370 | 180 | 90 | N/R |
| 18 | 13.0 | 3 | 210 | 2300 | 1500 | 1100 | 750 | 560 | 370 | 230 | N/R | N/R | N/R |
| 20 | 20.6 | 1 | 70 | 1400 | 960 | 710 | 480 | 350 | 240 | 110 | N/R | N/R | N/R |
| 22 | 32.8 | 0.5 | 35 | 900 | 600 | 450 | 300 | N/R | N/R | N/R | N/R | N/R | N/R |
| AWG | Ohms | Amps | Watts |
Maximum Recommended Cable Length in Feet |
|||||||||
*N/R: Not Recommended
*(1) From 0 up to 9100 feet.
*(2) From 0 up to 7800 feet.
*(3) From 0 up to 9900 feet.