12 volt underground???

gotrocks · Jul 16, 2004

Howdy Folks,
I've done a few searches but have not found anything.
My question is regarding running several hundred feet of underground wire that will carry 12 volts to power a few lights and a small pump.
What size "transformer" (charger)?? and wire size. I would like to run approx. 600 feet with a light every 100 feet. Also be able to run a 12 volt pump similar to one on my 25 gal sprayer at the end of the 600 feet.

Thanks for detailed information OR location of the source for information.

Plug me in and turn me on, then maybe I'll see the light. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/tongue.gif

_RaT_ · Jul 16, 2004

It will all depend on the size of the load. For practical purposes, running low voltage for any distance gets impractical very quickly. The voltage drop is severe. In other words, even 100' can quickly drop the voltage from 12 volts down to 6 or 7 volts without even much of a load. A better option is too bring 120 volts down the road and transformer it at the end. A simple 3/4" conduit buried in the ground with a relatively small wire size (again, depends on the ultimate load) will be cheaper then running a very large wire with 12 volts in it and be more effective.

boustany · Jul 16, 2004

Also, you are asking, essentially, how long is a string. How much current in the lights and pump? The drop will depend on the current and the distance and you will have to supersize the cable, likely.

So, you could approximate the voltage drop from the cable tables used for 110/220.

Why use 12 volts?

gotrocks · Jul 16, 2004

Thanks to you Two _raT & boustany
I was thinking 12V would eliminate danger of shock around the pond and was thinking an auto headlight would give ample light to the pathway. The marking on my Surflo 12V pump indicates 5A.
If 110 is the best way to go then I'll surely install GF breaker.
Even with 110 I could still use someone to "hold my hand" /forums/images/graemlins/confused.gif and tell me what size wire and amps for line. Example; run 100 feet install 100watt light, then repeat until the end of the line with 100watt light there. Total 6 lights.
Lights would be OFF when pump is used and would get a 110V "fountain pump" .
Thanks for more info and suggestions.

Bob_Skurka · Jul 16, 2004

Run 12 gauge underground cable, skip the 100watt light bulbs and pony up a little more money for 20 to 25 watt Compact Flourescent bulbs, and you will likely have enough power at the end of your string for a mini-pump. Voltage drop over 600' is going to be the problem you face. The 100 watt incandescent type bulbs will be drawing 600 watts over that 600 foot run and likely won't be fully powered. Switching to the energy efficient, although at about $8 each, much more expensive compact flourescent bulbs will give you full light output. I used to have voltage drop tables, and can not find them, but I built a pool house about 150' away from our main house and we were concerned about getting 15amps delivered just that short of a distance becuase of voltage drop. I'm sure we ended up with 12 gauge wire run through plastic conduit. You should be able to find voltage drop tables somewhere on the internet.

BB_TX · Jul 16, 2004

You can do a search for voltage drop calculator and find a bunch of them. Here is one .
Here is another .

slowrev · Jul 16, 2004

I agree with Rat, Tun 120 v out there and step it down if you want. power it from a good GFCI breaker or receptacle to avoid dangerous shocks. All outdoor or wet locations should be powered with a GFCI circuit for safety and code compliamce.

_RaT_ · Jul 16, 2004

The ShurFlo pump may also be 12V DC not AC. You introduce another problem since you will not be simply using a transformer anymore but rather a 12VDC power supply. At any rate, the typical scenario would be to run 120V down the driveway. For 600' you will need several pull boxes. All in all, with a little guidance, it's not difficult, you can do it. I would tend to run a GFI outlet at the end rather then a GFI breaker at the begining. For a long distance like that, the GFI will be easily fooled and trip's much easier even when no apparent fault is there.

JohnCt · Jul 19, 2004

best bet is to run 120 volt line.maybe even a #10 uf wire for that long a run.put the gfci at the begining of the run for full gf protection of the wire. gfci works on current flow, balance must be equal across both wires or the gfci will trip. lower voltage should not affect function. lightining can cause gfci to trip ( weather its located in the house or outside ).hope this helps.

moeh1 · Jul 21, 2004

#10 is probably a good bet for the load you reasonably expect to put on the circuit. I ran a 500' conduit a few years ago and spec'ed it for 20A, had to go to #8 to stay within 10% voltage drop. Beware that the tables you use correspond to the voltage you are running. You might consider a conduit run with a few outlets popping up along the way, you could always plug in some low voltage lighting transformers in these and still have the flexibility they offer, plus you last outlet might be able to be short of the 600' mark. If you are good with a heat gun you can bend all the plastic conduit and it is pretty easy and cheap to work with. Final point on a GFI, they are only good for about 250' of protection, if you go beyond that distance for wire after the GFI they will pop due to the timing lag. For my use,I ran conduit, popped up at 250' put in a GFI recptacle and a light on a post, went back down and ran another 250' to the spot I wanted power.
Good Luck!
Marty