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Old 10-20-2009, 12:48 AM   #1
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Outdoor lighting project


I am hooking up 12 500 watt flood lights and have to run a couple 2 gang boxes with switches. Can I run 10/2 from the breaker to the switch and 10/2 out for the first 100 feet then splice in 12/2 wire to avoid voltage drop? I have 6 of the lights 300 feet to 500 feet away from the switches. Or can I get away with running 12/2 wire all the way around and not have to worry about the voltage drop? Im ganna put 3 lights per 20 amp breaker.

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Old 10-20-2009, 05:34 AM   #2
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This isn't an answer, but if you really need 6000 watts worth of incandescent light, wouldn't you be better served by something more efficient and longer lasting such as sodium or metal halide?

Also, with all those new 500 watt lights running, that's 50 additional amps running through your panel (and your meter--oy!). Have you calculated your total usage, and is your service big enough to handle the new lights along with your existing requirements?

I'm not going to say outright that it's a bad idea without knowing the reason for your project and whether you have 100, 200, 400 amps, or more, but I am really curious what all these lights will be used for, and how many at a time for how long.

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Old 10-20-2009, 05:49 AM   #3
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Check the book for the Ohms per foot for your wire lengths.
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Old 10-20-2009, 07:29 AM   #4
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Originally Posted by Josh Jones View Post
Can I run 10/2 from the breaker to the switch and 10/2 out for the first 100 feet then splice in 12/2 wire to avoid voltage drop?.
The quick answer to your question is no.

Go 10/2 (or perhaps 8/2 on the 500 foot run) as much of the distance as is practical. (Assuming 3 500 watt lamps or about 15 amps per circuit.)

The greater the percentage of the run done with thicker wire, as well as the thicker the wire is, for a given draw in amperes, the less the number of volts dropped.

If you went with more efficient lighting (high pressure sodium perhaps) the number of amperes drawn will be less for the amount of light you get, and you can use thinner wires.

A 200 watt mercury lamp or a 100 watt high pressure sodium lamp (entire fixture draws a little more) will give about the same amount of light as a 500 watt incandescent lamp.

I don't have the math or resistance table handy to do the actual calculations needed and to verify whether 8 gauge wire is overkill.

As far as "for how long", the following is some technicalia. For wires sized properly for short distance, voltage drop does not change for either short or long distance if the lights are on for a long time. If we consider a "continuous" load, the wires need to be sized for 20% more amperes. A nighttime ball game would qualify as a continuous load, and if the 3 lights on the circuit are all on and draw 15 amps together, the circuit has to be rated for 18 amps which means 12 gauge wires. You need 10 gauge or fatter wires to combat voltage drop which makes the issue of continuous vs. intermittent load moot but you need heavy duty switches.
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Last edited by AllanJ; 10-20-2009 at 08:07 AM.
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Old 10-20-2009, 02:09 PM   #5
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Lets put this in perspective. You run 4, 500 watt lamps, @17 amps, 500 feet away from the panel.

This would require #2 Cu wire, @2.8% VD, 116.7 volts.

Consider less power consuming lighting. When you factor the cost of installing these circuits and the life of these bulbs, you will realize you are making mistake. Now, If money is no problem then have at it. Give us the first distance and the watts, the second distance and the watts and so on.
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Old 10-20-2009, 09:59 PM   #6
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The lady couldnt afford the metal hallide lights compared to the 500 watt lights.
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Old 10-20-2009, 11:47 PM   #7
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The first three lights will be no more than 100' from panel. So the the first 1500 watts will be fine on a 20 amp single pole breaker running 12/2 from circuit to heavy duty 20 amp switch, correct? Then the next 1500 watts will be about 200' from panel. Same situation put on 20 amp circuit and run 12/2 from circuit to switch and daisy chain lights. The next three lights or 1500 watts will be around 350' from panel. Then the last 1500 watts or three lights will be 500' to the farthest light fixture.
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Old 10-21-2009, 12:01 AM   #8
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Are you using the Quatz for dusk to dawn useage or what ??

First three will be fine with #12 conductor at 100 feet
Second three will need #10 at 200 feet but you may noted the quatz may be little dim with #10 however I will suggest #8 for this distance
Third set at 350 feet you will need #6
Forth set you will need #4

All conductor I listed above is copper.


Really I will suggest to you talk to that person to recondersering to go with HID like Metal Halide flood light due you will see why the cost of conductor will go more than what the HID will worth for and plus what with the HID you can get them in 240 volt verison you will use far much smaller conductor so that will really save the cost espcally the latter two runs.

Check with the conductor cost you will see why as I mention above

Merci.
Marc

P.S. I do work on parking lot luminares and I can best suggest this due from my experince with this set up and you will get simair comments from other readers they will tell you the simiaur message to ya

Last edited by frenchelectrican; 10-21-2009 at 12:13 AM. Reason: change the wording
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Old 10-21-2009, 06:29 AM   #9
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Sounds like someone is doing electrical work for hire that is not an electrician, and is over his head!
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Old 10-21-2009, 06:43 AM   #10
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Quote:
Originally Posted by Josh Jones View Post
The lady couldnt afford the metal hallide lights compared to the 500 watt lights.
This site is DIY for Homeowners
It is not for people doing electric work for hire
Please explain this comment
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Old 10-21-2009, 07:56 AM   #11
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but then again he could also be doing his 80 year old neighbor a favor? ... but when i think about it, if you're running that much wire, you probably have to trench it. And nobody is gonna do that for free...hmmmmmmmmm

And on top of that, you're not giving us any more information than just two lines. If you want help that is adequate you need to explain the situation to the best of your ability, not just two lines, or one reply "The lady couldnt afford the metal hallide lights compared to the 500 watt lights."

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Old 10-21-2009, 11:29 AM   #12
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Josh. You are not paying attention. Do you see the size wire you are going to need for the distance and load? Just the wire cost alone should be enough to cover the difference in fixture price.
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Old 10-21-2009, 07:23 PM   #13
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The person paying for the lights only had a certain amount of money to the project and really needed it done as cheap as possible. I gave her several options of how to do this and she told me her budget was what it is.

Yes its a favor for someone, and Im not an electrician for hire. I was asked to help someone out that is a family friend and thats what Im doing. I had a very simple question because she decided she wanted to change from 150 watts to 500 watts cause she had money left over and I said I could do it no problem without first looking at the voltage drop.

Last edited by Scuba_Dave; 10-21-2009 at 07:43 PM. Reason: language edited out by MODERATOR
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Old 10-21-2009, 07:31 PM   #14
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JV,

I looked at the metal halide and high pressure sodium but they were 220 dollars each. The flood lights are 10 dollars a piece. I never said its the smartest way its just the cheapest way I could do it for her. I explained the electric bill will go up but the lights will only be on 1 or 2 nights out of the week and only for a few hours so its not a continuous load.
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Old 10-21-2009, 07:31 PM   #15
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Using CFL's will really decrease the power used
I buy 65w CFL floodlights that = approx 300w reg bulbs
They were $15-25 each at HD with bulbs
---these usually have $15 off energy coupons
You could actually install 2x the lights & still use less then 1/2 the power

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