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Old 10-26-2011, 05:56 PM   #1
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What Gauge Wire do I need?


We just bought a new home out in the country. My daughter gets picked up at the end of the driveway for school, but the driveway is some 440 Feet long. It's rather dark in the mornings and is getting darker as the days get shorter.

We would like to add post lighting along the side of the driveway to make it more comfortable for her in the morning wait. I know this will require running some new underground wire for the light posts.

My wife found a great deal on some close out post lights at the big box store, and bought a bunch of them. They use 3 60 watt candelabra lamps per light, and we think 8 of them should make the walk in the morning bright enough.

I'm going to do the "heavy lifting" myself. Here is a crude drawing of what we're dealing with. The two lights by the house are already there. The ones we will add are along the driveway and at the tip of the turn-about.



The question is, what gauge wire do I need to do this project right? I ran it through an online wire gauge calculator and it came back as AWG 6 wire. It sounded like overkill to me, but I thought I'd ask the experts first!

Thanks in advance.

RJ

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Old 10-26-2011, 06:20 PM   #2
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What Gauge Wire do I need?


8 fixtures with 3 - 60 watt bulbs is 1440 watts or 12 amps. If you run #10 UF cable with a 20 amp breaker, you will have about a 10 volt drop or 110 volts to the lamps. That should work OK but if you use 40 watt bulbs or CFLs it would be better. Be sure this is a dedicated circuit and do not add anything else to it.

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Old 10-26-2011, 06:24 PM   #3
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Well, if you do use all 60W lamps then you will need a circuit just for these lights, and you WILL need #8cu or possibly even #6cu.

IMO eight posts is a bit overkill, and 180 watts per is also way overkill.
If it were me I'd probably do six poles and use CFL lamps to keep the wattage WAY down. This way you can get away with probably #10 wire.
Even if you do go with all 8 posts I would seriously consider either; heads that take a single lamp and use a single CFL, or use candelabra base CFL's in the heads you got.
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Old 10-26-2011, 06:26 PM   #4
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Thank you very much. Would it be okay if I ran TWO dedicated circuits to the lights using #12? That would be about 6 amps per circuit, right? (I have a spool of #12 UF that is about 1,000 feet that was left in the shed when I moved in.)

Thanks again. I appreciate your response.

I don't think CFL's are going to cut it, because CFL's in the winter cold take a LONG time to warm up. LED's maybe. CFL's probably not. Or are they better these days than they used to be?

I didn't think 60 feet apart was too much light, but perhaps you're right, Speedy.

I can change the recepticle in the head for a single standard bulb, I think, pretty easily. That may be a better way to go.

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Old 10-26-2011, 06:29 PM   #5
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If you can keep the wattage down to around 600 watts you can use #12 for the whole thing on the one circuit. CFL's or LED's will do this for you.

5 amps @ 120v @ 450' is a drop of just under 3%, or 3.5 volts. Way more than respectable.

The well over 1000 watts you are considering is the killer.
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Old 10-26-2011, 06:34 PM   #6
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What Gauge Wire do I need?


12 gauge UF will work on a 20 amp circuit, but you will have alot of voltage drop, and it may put some stress on the wire and the CFL's if you use them. Use CFL's, as they will save you energy, and you can run more on the circuit(s).

Minimum 12in burial if on a GFCI, and 18in if non-GFCI. Max 24in if you really want to have some fun.
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Old 10-26-2011, 06:48 PM   #7
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12 gauge UF will work on a 20 amp circuit, but you will have alot of voltage drop,
Well, that's what we've been discussing, but VD is directly dependent on load. So keeping the load low will curtail VD.
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Old 10-26-2011, 07:01 PM   #8
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I used a CFL in my outdoor lighting once. The winter here in Ohio really made that thing rather un-useable. Just wouldn't brighten up. LED's I think will work better and I'll start looking into them. Funny thing, the light fixtures themselves are going to end up being less than HALF of the cost of LED's bulbs for these lights!
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Old 10-26-2011, 07:28 PM   #9
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CFL's will work fine. You just have to turn them on 15 minutes before you need them in really cold weather.
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Old 10-26-2011, 07:34 PM   #10
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CFL's will work fine. You just have to turn them on 15 minutes before you need them in really cold weather.
Excellent. I see they also have CFL Outdoor rated lights as well that are rated to start at 0F. Thanks Speedy Petey. Your help is GREATLY APPRECIATED!!!
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Old 10-26-2011, 07:35 PM   #11
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What Gauge Wire do I need?


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Originally Posted by Speedy Petey View Post
If you can keep the wattage down to around 600 watts you can use #12 for the whole thing on the one circuit. CFL's or LED's will do this for you.
How would you calculate the load in this instance to see if you comply with the NEC? Is it the max rated wattage of all of the luminaires (can you tell I've been spending too much time trying to understand the NEC?) or can you get away with installing CFLs or LEDs and using the lower wattage in your calculation? Is this considered a continuous load subject to ampacity derating?

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Old 10-26-2011, 07:42 PM   #12
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How would you calculate the load in this instance to see if you comply with the NEC? Is it the max rated wattage of all of the luminaires (can you tell I've been spending too much time trying to understand the NEC?) or can you get away with installing CFLs or LEDs and using the lower wattage in your calculation? Is this considered a continuous load subject to ampacity derating?

Matt
This is not considered a continuous load.
Voltage drop is a suggestion in the NEC, it is NOT a rule. So we just attempt to wire to prevent possible VD. In an instance like this you can wire to prevent VD according to local conditions, such as using a certain type and size of lamp.
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Old 10-26-2011, 07:52 PM   #13
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60 watt candlelabra bases are nothing but high maintenance.
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Old 10-26-2011, 09:05 PM   #14
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If I may throw a wrench in the works.....

How about something different.....put in some solar cells....add a battery and use some 12V LED lights.

Put it all on a timer so they come on when you need them....and during the day the battery gets recharged.
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Old 10-26-2011, 10:49 PM   #15
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If I may throw a wrench in the works.....

How about something different.....put in some solar cells....add a battery and use some 12V LED lights.

Put it all on a timer so they come on when you need them....and during the day the battery gets recharged.
I would love to do this. However, the lot is heavily wooded and you can stand in the middle of the driveway, look up and see NO SKY at all. Hoping I can bait deer into the property, if I can get a couple apple trees to grow in the shade.

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