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1) The National Electrical Code recommends that the voltage drop be 3% or less. Using 240 volts @ 100 amps on a 330 foot run results in using 3/0 AWG Aluminum conductors with an insulation rating of type "THW" for wet conditions. The voltage drop on the 3/0 Aluminum feeder conductors will be @ 3% or a loss of 7.1 volts. Therefore, the 3/0 Aluminum feeders are code compliant.
2) The feeder circuit needs to be a 4 wire circuit comprised of 2 hots, 1 neutral and 1 equipment grounding conductor. The equipment grounding conductor needs to be a size 2 AWG Aluminum.
3) The 4 feeder conductors need a minimum of a (2") two inch trade size diameter Sch. 40 Gray electrical PVC conduit buried a minimum of 18" below final grade. In order to make the wire pull easier, I recommend to increase the conduit diameter to 2 1/2". The PVC conduit also requires expansion fittings at the elbows to allow for any frost heaving and/or soil movement.
Since you have a long conduit run, make sure you use plenty of Yellow wire pulling lubricant when fishing the conduit as well as when pulling the conductors.
I recommend to install a warning ribbon tape above the entire conduit run and place the tape around 6" below final grade. The warning ribbon tape will provide a warning to anybody digging in the future that an electrical line exists below.
I also recommend to pound a few metal stakes in the ground and spray paint them red and use these as nearby markers for the conduit run. Then create a final "as-built" drawing with dimensions referenced from the red stakes or the barn corners or property boundary lines. The "as-built" drawing will also provide documentation for any future trenching or digging near the conduit path in the future. Place a copy of the drawing in each electrical panel for future reference.
4) Since the barn is a detached building, you will require (2) two 8 foot ground rods spaced a minimum of 6 feet apart. You will need a 6 AWG copper wire as the grounding electrode conductor from the ground rods to the sub-panel equipment ground bar. The ground wire needs to be (1) one contiguous run from each rod to the panel.......ie........ no splices allowed. I suggest installing the 6 AWG ground rod conductor in 1/2" EMT metal conduit on the exterior and interior in order to protect the ground rod conductor from any damage.
5) At the sub-panel, you will need to install a separate equipment ground bar to land all branch circuit ground wires as well as the ground rod wire and equipment ground wire from the feeder circuit.
6) At the sub-panel, DO NOT install the green main bonding screw or a main bonding jumper strap. On all sub-panels, the neutral must remain isolated from the panel metal enclosure. By not installing the main bonding is how the panel neutral remains isolated. At the sub-panel, only neutral conductors will terminate to the neutral bus bar and never any ground wires. DO NOT inter-mix white neutrals and/or any bare copper or green insulated ground wires on the neutral bus bar as this will result in a code violation as well as create a safety hazard.
7) At the barn, all receptacles need to be GFCI protected.
8) At the 200 amp main panel, you will need a 100 amp double pole circuit breaker for the feeder circuit. I also recommend that the 100 amp sub-panel be a main breaker type and not a main lug type of panel. The 100 amp main breaker will be used as the "means-of-disconnect" at the barn.
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