I want to run 120Vpower 250 ft to my water tank for approx 8 -10 ft of heat tape (average 7 watts/foot of tape). The exposed pipe is wrapped with insulation which has been sufficient to protect it 16 out of the last 18 years, but the two times the temperature dipped well below normal caused it to crack. It's a pain to replace and I would rather prevent it in the future by installing the heat tape to be used if needed. Pipe freezing temperatures usually only last here for 3 or 4 days once every 5-8 years. In addition to the heat tape, I will probably put one weatherproof outlet at the tank for very infrequent use with a small power tool (like a drill, leaf blower or trouble light). What's the smallest, cheapest, easiest-to-run wire I can use? It will be buried in sch 40 3/4" or 1" electrical pvc conduit. Forget the codes-I am in the wilderness and no one cares as long as it works.

I think 12-2 UF would be the best choice as long as you aren't running anything that is really voltage sensitive. No need of conduit.

If you really want to go the conduit route, then use individual strands of 12 gauge THHN or THWN in the conduit. Make certain you use the correct colors; black, white, green. Inspection or no, not doing it correctly is just plain STUPID.

I should add that if I was doing it for myself I would use 10 ga wire. Who knows what the next person may want to use it for.

Please wait for verification on this suggestion.

I would suggest another method to bring power to this building. For example a solar panel at the building. Cabling is expensive especially if I have correctly identified the size of the conductors.

It looks like you will either need #4/3 w/ground copper or #2/3 al. w/ground. THWN or THWN(2) insulation to successfully bring 20 amp to the building and be within the recommended voltage drop calculation. Because this is going to be in conduit, which is considered a wet location, you need to use water proof insulation for all of the conductors.

As to the conduit, you would need Trade size #1 for copper conductors and trade size 1 and 1/4 for aluminum conductors. (see Annex "C" of the NEC 2008 book. Page 70-710)

Personally, I would use larger sized conduit in case I need to increase the feeder to supply a larger load in the future.

Since this is going to a remote building, you will need to put in a sub-panel with no more than six breakers.

GFCI Receptacles have to be used. Lights can be on a non GFCI circuit. Also, it is required that if you bring power to the building, you must put a switch controlled light at the entrance to the building.

Finally, you will have to build a grounding system at the building. That means a ground rod, EGC from the sub panel box to the ground rod.

Ground and Neutral must be isolated from each other at the sub-panel.

Good advice from both of you. I think I'll split the difference and try to get by with #8 wire. The conduit is necessary because of gophers, squirrels etc and it will be driven over occasionally. It's the voltage drop vs laying down a big heavy bulky hard-to-handle cable run that made me ask.

If you are not burying this deep enough to be protected from driving damage, nothing you do will be safe. Just make certain that you use the correct type of insulation (THWN) and colors for the conductors in the conduit and adhere to conduit fill requirements. Please, nobody remembers the bargain price or fast install when they have to repair something. You've heard of Murphy.

Well... If you follow the rules and consider voltage drop over that distance, #4 wire is needed to run a 20 amp circuit. Is this a building or just an outside installation? Give a few more details please.

Well....If you follow the rules and consider voltage drop over that distance, #4 wire is needed to run a 20 amp circuit. <snip>

I agree with the calculations, however for a 70 watt heater or a trouble light I don't see it worth the extra copper. If you want to run anything that has a significant current draw, then yes, go the whole way. Where I work there is a 20A landscape lighting circuit (inspected and approved no less) that is at least 400 feet to the end and the electrician did it all with 10-2 UF. The light strings in the trees don't seem to mind it and that load is probably 1200-1500 watts. The fluorescent sign lights at the end of the chain work just fine and I have no problems with the ballasts. I should check the voltage sometime just for kicks.

If the OP wants to reduce the copper consumption, he could label the circuit at both ends "LOW CURRENT USE ONLY". The worst that will happen is that he will burn his leaf blower out early. I really wonder what gauge wire they hooked the well up with.

Thank you, EPMiller. I just needed a little confirmation of what I would like to do which is run a heat tape when it drops below 20 deg, and have an outlet at the tank for whatever I might want to plug into it (with the caveat that the voltage might be low and cause damage). The tank sits by itself on a 10 ft high platform up on a hill. There is no building there. I have used the leaf blower there on 200+ ft of extension cord and it didn't burn out during it's 3 minutes of use. Perhaps it has a(n) universal motor. I have a 30 year old Homelite electric chainsaw that does. It's been run on 140v and 90v and is still going strong. I think I know better than to try to run a refrigerator off a circuit such as this. And thanks for the advice about burying deep. I will.

EP.. I have to agree with you. It's a temporary use outlet at best. I would consider 10-2 though. At this distance it won't hurt. Am I right in thinking that the pump to fill that tank is somewhere else? If not perhaps that circuit could be tapped for the outlet use.