Empty conduit is your best bet here. No point in guessing what (if anything) you may get, and guessing wrong. While you can leave a pull string in it, you can also just vacuum a pull string into it when the time comes (that's what is normally done to install it in the first place). If you do leave a string, don't worry about how big/strong it is: it can be used to pull in one big/strong enough when the time comes. Do make sure it won't rot while it's waiting. And CAP THE ENDS of the empty conduit, or it may not be as empty as it should be when you need to use it.
Speaking from personal experience, assuming you don't need more than one for excessive bends/sweeps (and do use long-radius sweeps when you do need to make a bend, not the short radius stuff from home centers) you will be much happier with a pull box/hand hole/access at the halfway point.
I have hand pulled (no winch) fiber over 600 feet. It was not much fun. With correct technique (pulling on the Kevlar, not the fiber or the jacket), possible, but no fun. 330 feet/100m it should be easy (was for us) if the conduit is configured correctly (large-radius sweeps, no more than 360 degrees of bending between access points.)
Enter (and leave) the pull box with 45s, not 90s. Leave some extra cable coiled up in the pull box in case of any future need for more at either end due to damage. Before pulling cable in, see figure 8 coiling and use it so you can pull the cable in, figure 8 coil the other half, flip the coil and pull it the rest of the way - no tangles.
For political/turf (rather than electrical) reasons, it's often best to keep cable, telephone and "whatever is next" in separate conduits. It's also much less practical (or more difficult) to pull into a conduit with a cable in it - often best to remove the original cable and pull the new cable and the original cable back in together, rather than trying to pull a new cable in next to the original - but best if you can just pull the new cable in its own conduit and leave the original cable/conduit alone.
Additional suggestions -
- If using PVC conduit, choose schedule 80, and deburr (remove sharp inside edges from) the male ends of the joints.
- If you can get polyethylene conduit, consider it as you can get
100 meters with no joints and it's more flexible than PVC
(effectively the same as polyethylene water pipe, with different
certifications stamped on it)
- Do not neglect the locating/warning tape - whether it says buried fiber optic below or buried telephone line below does not matter nearly as much as that it is there in the top of the trench, directly over but well above the conduits.
Base Conductor Size
Start out by using Table 310.15(B)(16), and applying any required corrections, to determine what size conductors you'll need. For your situation, we'll assume we can use the 75°C column, that you want to use copper conductors, and there's no other corrections required. So in your case, if you want to install a 50 ampere panel, you'll need at least 8 AWG copper conductors. If you want a 60 ampere panel, you'll need 6 AWG copper conductors.
Voltage Drop
Once you have the base conductor size selected, you'll want to calculate the voltage drop across that size conductors for the length of the feeders. The first step here will be to use Table 8 from chapter 9 of the NEC, to determine the resistance of the conductors you've selected.
In your case, 8 AWG stranded copper wire has a resistance of 0.778 ohms per 1000 ft. 6 AWG stranded copper wire has a resistance of 0.491 ohms per 1000 ft.
Next you'll use the following formula, to calculate the voltage drop across the feeders.
V = L * 2 * R * A
Where:
- V = Voltage Drop
- L = Distance along the wire from one breaker to the next.
- R = Resistance per foot of wire.
- A = Current running through the conductor.
For a 50 ampere circuit, 130 ft. long, using 8 AWG stranded copper conductors, the calculation looks like this...
V = 130' * 2 * 0.000778 * 50 A
V = 260 * 0.000778 * 50 A
V = 0.20228 * 50 A
V = 10.114 V
10.114 V is 4.2% of 240 V. The NEC recommends having a voltage drop less than 3%. To achieve this, you're going to have to use larger conductors.
6 AWG stranded copper conductors have a resistance of 0.000491 ohms per foot, which means the voltage drop would only be 6.383 volts or 2.7%.
For a 60 ampere circuit 130' long, 6 AWG stranded copper conductors would have a voltage drop of 7.6596 volts or 3.2%. While 4 AWG stranded copper would be 4.8048 volts, or 2%.
Conductor Type
Once you know what size conductors you need, you'll have to determine what type of insulation the conductors should have. Since you're burying the conduit, you'll need a wire rated for wet locations. The popular choice in this situation, would be to use THWN wires.
Wire Size
Now that you know what size conductors, and what type of wires you'll use. Then next step is to determine the physical size of the wires, and how much space they'll take up in conduit. For this, you can use Table 5 from chapter 9 of the NEC. There you'll find that 6 AWG THWN wires have an area of 0.0507 square inches, while 4 AWG THWN wires have and area of 0.0824 square inches.
Conduit Fill
Using the size of one wire, you can figure out the area required for all four wires.
0.0507 * 4 = 0.2028 in.sq.
0.0824 * 4 = 0.3296 in.sq.
Use Table 1 from chapter 9 of the NEC, to determine the allowable conduit fill percent. Since you'll have more than 2 conductors, you can fill the conduit to 40%.
Conduit Type
If you know what type of conduit you're using, you can use Table 4 from chapter 9 of the NEC to look up the area fill values for various sizes of conduit.
Conduit Size
Since you've decided to use Schedule 80 PVC, you'll simply find that table in Table 4. Then look down the 40% fill column, until you find an area large enough for all your wires.
In your case four 6 AWG THWN conductors, will require 1" Schedule 80 PVC. While four 4 AWG THWN conductors, will require 1 1/4" Schedule 80 PVC.
Conduit Size Alt.
If you don't feel like calculating wire/conduit area, and all the wires are the same size, you could use Table C.9 from Annex C of the NEC to look up the conduit size required. There you'll find that you can fit five 6 AWG THWN wires throug 1" Schedule 80 PVC, and that you can fit six 4 AWG THWN wires though 1 1/4" Schedule 80 PVC.
tl;dr
- For 130' long 50 ampere feeder, use four 6 AWG stranded copper THWN conductors though 1" Schedule 80 PVC.
- For 130' long 60 ampere feeder, use four 4 AWG stranded copper THWN conductors through 1 1/4" Schedule 80 PVC.
NOTES:
- This answer contains some of the tables used in this answer.
- If you don't feel like doing any maths, you can surely find a calculator online to do all the work for you.
Best Answer
Your bigger problem is running out of allowable bends (or pullable bends between access points,since pulling near the max allowable is a bugbear and often beyond the ability or available tools of DIYers. You end up humiliatingly having to call an electrican simply for the pull, and once called they want the whole job.
I would consider a conduit body right at the upper vertical bend.
Conduit bodies are 90 degrees, so I would add a slight ~20 degree bend onto the short conduit coming out of the access panel, to tuck it upward slightly, so it is perpendicular to the angle of the outside wall. Then, when you make your 90 degree with your conduit body, you come down at the correct angle. That will also mean you face less than 180 degrees of bend through the underground section, still in the DIY-pullable range.