wire size check

[kaffine]

I want to install an outlet near the base of my driveway. My plans are to use it to power a camera and driveway sensor and a copper to fiber converter for the data. I may also use a power tool on occasion. The problem is the distance, 500 feet from the main panel to the bottom of the driveway.

I was thinking of using 8awg copper but after looking at some of the voltage drop calculators they are saying I need to use 4awg copper or 3awg aluminum. Am I doing something wrong on my calculations or do I really need that large of a wire due to the distance? I assumed 16 amp load since breakers should only be loaded to 80%.

Although after looking at the price of conduit and copper wire it might be cheaper to go with 2-2-2-4 direct bury aluminum than the conduit and 8awg wire I was planning on. I am only going to trench this run once I would rather do it right the first time.

 

[Speedy Petey]

I want to install an outlet near the base of my driveway. .............. The problem is the distance, 500 feet from the main panel to the bottom of the driveway.

I was thinking of using 8awg copper but after looking at some of the voltage drop calculators they are saying I need to use 4awg copper or 3awg aluminum. Am I doing something wrong on my calculations or do I really need that large of a wire due to the distance? I assumed 16 amp load...............

We use the actual or calculated load, not a maximum load.

......... since breakers should only be loaded to 80%.

This is completely false. It's an old wives tail perpetuated by folks who are not familiar with codes and only go by what they are told over the years.

The occasional power tool is going to be your kicker. IMO wire it for the actual load and get a generator for when you need a circular saw down there, or anywhere else.


Assuming an 8-10A load (well over your actual load IMO) you can use #4cu for 500'. A 5-6A load can go down to #6cu.
This is NOT a cheap endeavor.

 

[sberry]

I looked at this last night but passed, I agree with Speedy here except the actual will likely see an amp. I got 300 ft of 16 and it runs a small lamp, 40 or 50 watts. I was going to put 100 watts in and measure V for giggles and see.

 

[laser3kw]

Assuming an 8-10A load (well over your actual load IMO) you can use #4cu for 500'. A 5-6A load can go down to #6cu.
This is NOT a cheap endeavor.

If the op was just powering the camera and sensor, what size would it take? I would guess a camera and sensor would be < 2 amp (basic assumption 120v)?

 

[RickP]

I looked at this last night but passed, I agree with Speedy here except the actual will likely see an amp. I got 300 ft of 16 and it runs a small lamp, 40 or 50 watts. I was going to put 100 watts in and measure V for giggles and see.

I've got a similar setup, only my driveway is longer, so I used 14-3 UF direct bury cable (with one circuit switched at the house). My lights are only about 200 watts, so I calculated the voltage drop with a 2 amp load. My drop is 7 percent, or about 111 volts at the lights. That's fine with me, because they're only lights. I'll occasionally use a drill or a saw out there, but it's so infrequent that I don't worry about the voltage drop.

 

[doan]

12-2 UF is probably the most practical price point. slightly more than 14, but anything bigger will cost you big time.

 

[wyliesdiesels]

12-2 UF is probably the most practical price point. slightly more than 14, but anything bigger will cost you big time.

If youre talking about using #12 wire at the OPs distance of 500' with an 8a load(going with the load others are suggesting) that WONT work! The voltage drop will be so horrendous, that most devices wont turn on! The voltage at the end would be about 104v IF the voltage at the start of the #12 is 120v. Any lower and the voltge at the end will obviously be lower!

 

[pattenp]

My suggestion is to use direct bury URD such as aluminum #4-4-4 Triplex Secondary UD. At 120V you should be good for loads around 8A to 10A without VD over 5%. If you go with #2-2-2 you should get up around 15A with less than 5% VD.

 

[Stuart in MN]

If youre talking about using #12 wire at the OPs distance of 500', that WONT work! The voltage drop will be so horrendous, that most devices wont turn on! The voltage at the end would be about 104v IF the voltage at the start of the #12 is 120v. Any lower and the voltge at the end will obviously be lower!

It depends on the current load at the far end...the original poster said, "plans are to use it to power a camera and driveway sensor and a copper to fiber converter for the data." That will only be a couple amps; I used the online Southwire voltage drop calculator, assuming 120vac, 3 amps, a 5% voltage drop and 500 feet, and it said #12 would work.

However, if he also wants the ability to plug in a power tool of course the wire will need to be upsized.

 

[theoldwizard1]

Tesla coils.

 

[KenB]

Use transformers at both ends -- step up the voltage before the long run and step it back down at the destination -- to reduce the wire size needed. That's how the power company does it.

Ken

 

[tfi racing]

Sounds like an ideal application for solar,just give up on the power tools,it would be smarter to buy a generator and wheel it to the end of the driveway when you need it.

 

[madosta]

Tesla coils.

Thank you! Finally with some sanity. I was thinking high voltage and a step down pad at the site, but Tesla Coils FTW!!!

 

[brewchief]

I've run saws and drills off crappy generators feeding several hundred feet of tangled up extension cords, even with a generator set to idle down with no load they still work. I wouldn't worry about the voltage drop for occasional use, if it's going to be more then occasional then I would worry about it.

If I had to run #2 or the like I think I would end up simply running it to a small subpanel to make dealing with the large wire into a single receptacle issue.

 

[theoldwizard1]

Use transformers at both ends -- step up the voltage before the long run and step it back down at the destination -- to reduce the wire size needed. That's how the power company does it.

Ken

Actually a very good idea ! You can find used 240/120 transformers cheap. Run it backwards and you will have 240V out. Normal 14-2 UF will handle that no problem.

Now the far end requires some "creativity" ! After you figure out the voltage drop with a load, you either need a multi-tap transformer or a custom wound transformer (not as crazy as you might think for low current). Or possibly just a 208V to 120V transformer (208V is about 15% voltage drop from 240V).

(Transformers are sized by KVA = 1000 Volt Amps, or approximately 1000 watts. A 120V - 240V 1.5KVA transformer at peak would draw around 13 amps. At the far end, I would install a 10A breaker/fuse on the output side of the transformer)


Or 200-240VAC battery charger, a lead acid battery, and a DC/AC inverter.

 

[BFBOB]

conventional cameras, even with IR illuminators, seldom draw over 175mA at 12V. An IP camera will draw more, but not much. Your fiber data converter and vehicle sensor will be about the same, or less. Reread: AT TWELVE VOLTS. Your POWER consumption is about 12 Watts. That's 1A at 12V. At 120V, it's only .1A. Yes, 100 milliamps., one tenth of an Ampere. Now, you'll need a power supply to convert that 120VAC to 12VDC, and they aren't 100% efficient. Say it's only 50% efficient. Your current draw is still only 200mA (1/5 Amp). NOW redo your calculations and you'll see that voltage drop is not an issue with 14ga.
I'd use 12ga anyhow just for the increased mechanical strength if you're going the direct burial route. OTOH, 14ga in conduit is probably stronger, and only has to be buried half as deep.

 

[Speedy Petey]

I disagree with the step-up/down ****** idea. IMO that is WAY more work and cost than it's worth.
Just to avoid up-sizing the wire? Nope, not worth it. Especially for such a tiny load.

If the load is going to be just the cameras and electronics, I'd go with #10 and be done with it.

 

[LXCam]

10 amps, 500ft, #8 awg copper = 6.4V drop or 5.3% well within the realm of a functioning circuit for the occasional skill saw routine. Assuming 120V BTW.

Even at 15 amps it's 9.6V or 8%

 

[kaffine]

Thanks for the info. Looking at the price for 2-2-2-4 aluminum it seems to be about $1.30 a foot. Not too bad. Not sure if I really want to try and run 500 feet of wire that heavy though.

I might just say I wont use power tools down there and just go with smaller copper wire. Even at 8 gauge copper it looks like it would be cheaper to go with the larger aluminum wire though.

 

[wyliesdiesels]

It depends on the current load at the far end...the original poster said, "plans are to use it to power a camera and driveway sensor and a copper to fiber converter for the data." That will only be a couple amps; I used the online Southwire voltage drop calculator, assuming 120vac, 3 amps, a 5% voltage drop and 500 feet, and it said #12 would work.

However, if he also wants the ability to plug in a power tool of course the wire will need to be upsized.

Yes, I was in a hurry and forgot to put 'AT 8amps'! Ive corrected it!

10 amps, 500ft, #8 awg copper = 6.4V drop or 5.3% well within the realm of a functioning circuit for the occasional skill saw routine. Assuming 120V BTW.

Even at 15 amps it's 9.6V or 8%

How did u come up with 6.4v drop? I did the math by hand and with a voltage drop calculator and got 7.8v at 10a, which is 6.5% and almost 112v.

And that must be a small skill saw because my mag 66 draws 14a running.

At 15a, I got 11.7v which is 9.8% and too low!

Thanks for the info. Looking at the price for 2-2-2-4 aluminum it seems to be about $1.30 a foot. Not too bad. Not sure if I really want to try and run 500 feet of wire that heavy though.

I might just say I wont use power tools down there and just go with smaller copper wire. Even at 8 gauge copper it looks like it would be cheaper to go with the larger aluminum wire though.

So we can stop bantering back and forth over wire size, Why dont u figure out what the total load will be and then post it here. If u do forget about using tools, #12 may actually work depending on load!

 

[kiatech]

Make sure you get Al approved material and nolox.

 

[pattenp]

Why are you looking at and pricing 4 conductor cable when you only need 3 conductors?

Thanks for the info. Looking at the price for 2-2-2-4 aluminum it seems to be about $1.30 a foot. Not too bad. Not sure if I really want to try and run 500 feet of wire that heavy though.

I might just say I wont use power tools down there and just go with smaller copper wire. Even at 8 gauge copper it looks like it would be cheaper to go with the larger aluminum wire though.

 

[LXCam]

How did u come up with 6.4v drop? I did the math by hand and with a calculator and got 7.8v at 10a, which is 6.5% and almost 112v.

And that must be a small skill saw because my mag 66 draws 14a running.

At 15a, I got 11.7v which is 9.8% and too low!!

One of these:
http://www.buildersbook.com/Merchant2/graphics/00000001/5060.jpg

 

[wyliesdiesels]

One of these:
http://www.buildersbook.com/Merchant2/graphics/00000001/5060.jpg

Weird! Calculator must be computing wrong!!

12.9x2x10x500= 129000 / 16509= 7.8v!!