I have a chicken coop that sits approximately 100' to 120' from a pole barn. I have wired the coop with a 20amp receptacle and three lights. I will be building a garden shed near the coop and will need a receptacle and lights in there as well. The receptacle in the coop will be used for a heated waterer and probably a heat lamp in the winter and probably nothing continuous in the summer. The receptacle in the shed would be used mostly in the summer for occasional power tools or small items. My plan to wire this would be a 30 amp breaker from main in pole barn, 10/2 wire buried to the coop. At the coop I am not sure if I need a sub panel or can I just run it into a plastic box and split it: running to the receptacle/lights in the coop and continuing on to the shed where I would probably have the same set up.(feed run to one or two receptacles and then to the lights) I don't forsee the receptacles being used at the same time for anything heavy duty and have no problem unplugging the waterer/heat lamp in the winter if I needed to run a power tool. What size wires would you use for each run? Thanks for the help!

If you had 20 amps of load, you would need #8 wire to deliver 120 volts -3%.

With #10 you could use 10 amps and stay within 3% of 120 volts.

If you use a 20 amp breaker ,then you can have the coop and shed on one circuit.

If you use a 30 amp breaker you will need to install a 2 circuit subpanel, then change to two 15 or 20 amp circuits.

Heat lamps and incandescent still work with voltage drop, Motors such as drills and saw do not work well when the voltage drop is too high.

You have some choices to make.

Thanks for the answer. If you are telling me a 20 amp breaker is sufficient to do what I have described than that sounds like the easiest and cheapest way to run the wiring. I would run the #8 to avoid any problems with voltage drop. Just to verify the complete set up. Run #8 to a junction box and split it(when I say split I mean connecting the branches to the #8 with wire nuts? ) running 12/2 to the existing 20amp receptacle in the coop which then continues on with 14/2 to the three lights. Then from the junction box run 12/2 to a future 20 amp receptacle continuing on to future lights with 14/2? The distance from the coop to the shed would be 30 feet at most. Is voltage drop a problem where I would need to run #8 wire from the split to the new building or would 12/2 be sufficient. I don't care to do it right the first time to avoid future issues. Have I maxed out this arrangement completely or could I extend from the shed further in the future? Nothing planned now..

Yes, split the #8 to two directions at a junction box, one to the coop and one to the shed, using all#12 wire, since you will be using a 20 amp breaker.

#14 wire not allowed on a 20 amp circuit.