At 200 feet you'd be looking at #1 copper (THHN, THWN) or#2/0 aluminum cable, assuming 100 amps with no more than a 3% voltage drop. From what you describe your needs to be, 100 amps sounds like overkill. Given the cost of that much wire, you might want to sharpen your pencil when doing your calculations.

Understand, that voltage drop calculations need the actual load you expect to carry NOT just what the size of the breaker feeding the panel is (or the sum of all the proposed branch circuit ampacities). Assuming 80A (80% of 100A), 2/0 COPPER would be required to avoid more than 3% voltage drop.

Note that if you are planning a pool there are ADDITIONAL things you need to be aware of. The ground MUST be insulated all the way back to the house.

If you're wiring underground you MUST use wet rated conductors. THHN is NOT permitted (though you probably won't find THHN that isn't also marked THWN which is wet rated).

You must have a ground rod even at an RV pedestal if there's more than one circuit there.

When you actually get around to building this out remember that the outdoor outlets need GFCI protection and wet rated in-use covers. There are so many concerns about things powering pool equipment and around pool that I can't go into here. Understand that large tanks of water where you intend to immerse yourself and family is no place for DIY duffers. We lose a person a year or so to improperly wired pool lights alone. You need to fully understand all of article 680 or hire someone who does.

Ron,

How did you come up with 2/0 copper? I ran it through two online voltage calculators (Southwire and somebody else). Both returned #1 copper at 100 amps, 240 volts, with <3% voltage drop.

What am I missing?

Let me run it again 1/0 gives 3.28% voltage drop

2/0 gives 2.6%

1g gives 4%

Are you using 200 feet?

Ron,

I posted a screen shot of Southwire's calculator above. If I input 200 amps and 100 feet, I get 3/0 copper. Is it possible that you transposed numbers? If I'm doing something wrong, I want to understand my mistake.

I got different voltage drop results from different online calculators, so I ran the numbers by hand for 200 feet, 240 volts, and 80 amps. I used resistance tables for AL and CU wire at 25 deg C and adjusted to 60 deg C with the temperature coefficients for copper and aluminum.

AWG 1 copper has a resistance of 0.145 ohms per 1000ft at 60 deg C. For 400 ft (round trip) we get 0.058 ohms. By Ohm's law, I = E/R or E = IR, 80 * 0.058 = 4.6v or 1.9%. Not bad.

AWG 2 copper is 0.181 ohms / 1000' at 60 deg, or 0.0736 ohms for 400'. We get a voltage drop of about 5.8v or 2.4%. Still under 3%.

But with the complexity of the code tables I tend to just take the 60 deg C column as a guide, and therefore I wouldn't protect #2 at 100 amps. Ron may have some thoughts on this, but if I were using copper, I'd use #1, which you can protect at 110 amps.

However, AGW 1/0 aluminum is 0.185 ohms per 1000' at 60 deg C, so here it would have a voltage drop of 2.5%. And if I'm reading the tables right, it can be protected at 100 amps at 60 deg. So that would probably be my choice.

After saying all that, I have to add that you're embarking on a fairly large project here, with more safety considerations than your average DIY task.

I may be making unfounded assumptions, but you seem to be describing a property of significant value. Given that, it may be worth considering having a knowledgeable pro do this work. IMO that would be in the interest of preserving your property's value, protecting the lives of family and friends, and avoiding potential liability.

Hi all,

First, thank you all very much for your input. I was away all weekend with poor cell service and no laptop, and I hate trying to type on a phone!

This future pool area electrical will be permitted and I am planning on using a qualified electrician - I'm thinking to use someone recommended by a reputable pool company as I imagine your run-of-the-mill generic indoor tract home stuff is different than outdoor, underground, large gauge, pool-related, etc. The safety of my family and friends is paramount, as is avoiding any long-term liability.

As with other house projects, experience has shown me that I'm better off pre-understanding everything to the best of my ability so that I can select, communicate with, and challenge any professionals where I do need to retain one. I find that I do many things better myself, but I will certainly admit that I do not have the personal experience with this type of wiring and it's critical to get right. My engineering background generally gets me over-thinking or over-working a problem, but it hasn't steered me wrong yet, and ultimately landed me here to make sure I am approaching this correctly so I am happy about that!

I tend to oversize things, which I think is generally better (not too many people come back and say "Gee, I'm sure glad I went with the smaller panel and circuitry," but they do say "Dang, I'm out of capacity, I wish I would have gone bigger!") That said, I am trying to avoid making the conduit and wiring so large that it's difficult to interface with later in terms of future connections, into the planned in-ground vault, etc.

I get the feeling that my initial 100A "worst case plan" is maybe waaay overkill, and I do need to put more thought into what my total appliances, etc. are and get amperage on them, and then make some assumptions about what total amperage may be running at any given single time, then hopefully that will inform my conductor sizing decision. Perhaps I'll find that I can downsize significantly.

For now I'm just trying to decide what size conduit to put in the ground at this phase that for sure won't be undersized, as I am covering it up with concrete in the next few weeks or so. It sounds like I'll want to keep the voltage drop under 3%. If I did go with the worst case 100A and let's say that requires #1 copper per Mike Kaiser & David R (I'm curious to understand the difference between their conclusion and Ron Natalie's), I'd need qty (3) current-carrying #1 conductors, and a single #6 insulated copper ground to join sub-panel to main (see attached screen shot for size per NEC Table 250.66 for Grounding Electrode Conductor; based on other reading I think you don't consider it equipment grounding, rather conductor grounding, but please correct me if I am wrong).

Per the conduit fill table (see attached screen shot), 2" Schedule 80 PVC can accommodate qty (7) #1 conductors and 1.5" Schedule 80 PVC can accommodate qty (4) #1 conductors. Over a 200ft pull, I'm assuming one would be ill-advised to go with 1.5" which can only just barely take the qty (4) sizeable conductors, so then the final question is:

Will 2" be plenty to pull the worst case conductor size over this length? Again, I think I will only have 2 elbows due to consolidating into an electrical vault in the driveway with other items before crossing into the house. I don't have experience on long, heavy gauge pulls that's for sure! Looking at the cost, it's like a $30 so that's no reason not to.

Thank you again for all your input.

- Danny

Danny,

I too would want to be well informed before hiring a professional. Understanding that I'm not a professional, I think for the grounding conductor from the service panel to your backyard sub-panel you would use Table 250.122. I also think that Table 250.66 is for the conductor to the earth ground (aka ground rod). In this case, they appear to be the same size but I think that the conductor to the earth ground needs to be solid.

I have no idea why Ron's sizing is so different than mine. It seems straight forward enough that a simple calculator should work. While I don't have 200' of backyard to run a sub-panel, I still want to understand how these things are calculated.

I posted a screen shot of Southwire's calculator above. If I input 200 amps and 100 feet,

As I stated, the poster said it is TWO HUNDRED FEET not 100. I asked you to confirm that distance in your calculations.

I calculated voltage drop at 200 feet of run and got AWG 1 copper too. I used 400' of conductor for my math (see above).

I tried a couple of online voltage drop calculators and got different answers from each, so I did the calculations manually. I used tables of AL and CU wire resistance at 25 deg C, and adjusted the resistance to 60 deg C.

I wonder if some of the online calculators are defaulting to 120 volts. If you have a voltage drop of (for example) 7 volts, that's 2.9% of 240 volts, but 5.8% of 120 volts. We're talking about 240 volts here, right?

Danny, you always want to run the largest conduit possible and affordable. The larger the tube, the easier the pulling.

I suspect that is the difference, indeed. Should have looked at the absolute voltage drop rather than the percentages.

Yes, 240V feed to sub-panel. Glad we seem to have found the discrepancy. So, #1 gauge copper is my worst case to do the 200ft at 100A. Realistically, I'll end up smaller once I determine true likely amperage.

DavidR, agreed, the larger the better. Where I'm struggling due to lack of personal experience, is whether or not 2" DIA is already plenty oversized to make for an easy pull with the 200ft of qty (3) #1 conductors + single #6 insulated copper ground wire.

Anybody have any thoughts on that? Should I go 2.5"? I want to go plenty big, but within reason...