I have a bid on residential post lighting job.The customers driveway is 1200 ft long. He wants 10 post lights installed. I figure 100w per post light.Trying to achieve 3% vd, I'm looking at #2 copper for the run. My question is about the what size breaker to use.Base the breaker size on the load ? Also the customer want a receptacle 1000' up the drive way. I can use the same feed but splicing smaller conductors to feed the outlet ? Any help as always is greatly aprreciated.
I can't help with your design. Conflict of interest,but you are on the right track. Having seen similar installations the voltage drop is only on the main run. At the breakers and the loads, splice / branch to smaller conductors. The few feet at that point will not affect voltage drop. What ever you do, do NOT trim strands off the #2 to make it fit in a terminal. Good Luck. Alan--
This may not be helpful, but as a reality check. If this is out for bids, the other contractors will probably be bidding the job in 12 ga. wire. While the voltage will drop beyond 3%, you can buy a lot of 100W bulbs for the price of wire you're planning (won't the low voltage actually make the bulbs last longer?).
If this is your job, then I'm all for doing it right. If it's not, good luck selling the benefit of low voltage drop at a major increase in cost.
Interesting challenge. Judging form that 1200'drive the customer may not be living on a shoestring so you may have an opportunity to do a sales job selling him on the BEST solution to his project, approaching it differently from your competitors. You could provide him with (2-3) options, with incandescent lights with cable priced to deal with voltage drops, fluorescent lighting with applicable cable, and an alternate with the 480v distribution. If your customer likes your idea what you don’t want to do is to have him use it against you and ask your competitors for a requote. Increasing the cable size to reduce the resistance in order to reduce the voltage drop is one consideration. Have you taken into account the cost of the cable and the cost of a means to terminate it? When you made reference to (10) 100w one thinks about standard incandescent lights. Have you considered fluorescent lights which could provide the same light output but a lower wattage? With lower wattage there would be less voltage drop. Then, that cable will cost a fortune the combine that cost with the grief with terminating it. Have you though about trading the cost of all of the heavy cable for a 1500va 480v-240v transformer used to step-up the voltage to 480v to distribute the power a 480v, install a 150va 480-120V transformer to step down the power at each lamppost. Just think, 1/4th the current to deal with. So smaller cable and less voltage drop. Dave
Distribute at 240V, use compact floursecent fixtures (26W should be about the same light as a 100w incandescent, with a lot less maintenance and energy!). Use electronic multi-Volt ballasts, which don't care as long as the voltage is between 120-277
I would recommend using Jon’s suggestion of a multi-wire circuit. Pulling one additional wire will change your 8.3 amp 120 volt circuit into a 4.2 amp 240 volt circuit. I haven’t done any calculations but would guess you could get away with #8 or even #10 conductors and be within your desired 3% voltage drop. Make sure you calculate each segment of the circuit not the full load at 1200’. This would take care of the lights but not the receptacle. You really need to know what is going to get connected to the receptacle to figure the drop. The customer might be willing to forget the receptacle if they realizes how much additional the larger wire will cost. If they definitely want the receptacle I would consider running a separate circuit just for it which will save splicing the larger conductors at each light.