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We're planning to install some area lights in the farm yard, and want to be able to turn them on from the house. This is simple enough with normal house switches, but I'm concerned that the overall distances are going to cause problems with wire resistance. We're looking at a total circuit length in the hundreds of meters range, probably with 20A @ 110V worth of total lighting, let alone the wire load. Should I be concerned? Is there a commercially-available switch solution that I can readily employ? What do large facilities do for this sort of thing?

I know a fair amount about residential electrical wiring, but I'm no electrician.

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  • \$\begingroup\$ Is there an existing power source where the lights are going to be installed? \$\endgroup\$ – Spehro Pefhany Oct 8 '16 at 6:59
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If there is an existing power source where the lights will be installed you can use a lighting contactor to control the lights. Then then control wires will only need to carry maybe 20W-50W rather than 2kW your lights will draw.

They generally need to be mounted in an electrical box to protect them from the elements.

If the coil draws 40VA then 200m of AWG16 wire (400m round-trip) would be about 5 ohms and would drop less than 2V, which is more than acceptable.

Check your local electrical codes for compliance requirements for the components and installation.

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With 20 A @ 110V I asume that you intend to use standard light bulbs. If we take 50W for each bulb then you end up with 44 armatures. Changing them into LED lamps would change the load from 50W to 8-10 W per armature. As a result all would end up at only a max of 440 W. This amount of power can be handled without any problem by a standard light switch.This way you would save you the effort of using a lighting contactor and you would save energy. If you intend to make a complete round trip it would not be a bad idea to install two strings of 22 lights and connect both strings together inside the house of use a double switch or even two groups. Apart from even lower voltage loss it would be less troublesome to find the problem in case one might develop. For the cable you can still use AWG 16. The small voltage drop is of no importance since the electronic regulator in the LED lamps correct for that. Please consult your local regulations before installing.

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