1) National Electrical Code recommends that the voltage drop be 3% or less. Using a 100 foot feeder circuit @ 240 volts and at 60 amps, this results in using 6 AWG Copper for the sub-panel feeder circuit. Voltage drop on 6 AWG copper will be 2.4% or a loss of 5.7 volts. Therefore, code compliant for 6 AWG copper.
2) Yes, you can install 6/3 Underground Feeder with a bare copper equipment grounding conductor. The UF cable needs to be buried a minimum of 24" below final grade. Personally, I recommend to install Sch. 80 gray electrical PVC conduit as UF cable can fail over time due to shifting soil conditions as rock heaving, punctures, etc. A minimum of 1" Sch. 80 gray electrical PVC would be required using a quantity of (3) three 6 AWG Copper conductors rated as insulated type "THWN" and (1) one 10 AWG Copper, type "THWN" for the equipment grounding conductor. All sub-panels require a 4 wire feeder circuit comprised of 2 hots, 1 neutral and 1 equipment ground. Sch. 80 PVC conduit needs to be installed a minimum of 18" below final grade. Therefore, less digging/trenching using PVC conduit as compared to UF direct burial cable:)
3) Since a detached building you will need two 8 foot ground rods installed at the outbuilding spaced a minimum of 6 feet apart. Use 8 AWG Copper for the ground rod conductor to the sub-panel. The grounding electrode conductor (8 AWG copper) will terminate to a separate equipment ground bar at the sub-panel and NOT to the neutral bus bar.
4) I recommend installing a 60 amp double pole breaker at the main panel for the feeder circuit and purchase a main breaker panel to act as the sub-panel. The main breaker in the sub needs to be a minimum of 60 amps. 6 AWG copper will support a maximum of 60 amps.
5) I recommend the following branch circuits at the sub-panel:
A) Dedicated 20 amp/120V for the A/C unit
B) Dedicated 15 amp/120V for the lighting
C) Dedicated 15 amp/240V for the filter
D) Dedicated 20 amp/120V for the Dust Collector
E) Dedicated 20 amp/120V for the remainder of receptacles
All 120V receptacles need to be GFCI protected.
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. Only land white neutrals to the neutral bus bar and never any bare copper grounds on the neutral bus bar. All copper grounds will land on a separate equipment ground bar that you must purchase separately.
7) For the 100 foot run, I recommend to install a "Warning Ribbon" tape approximately 6" below final grade above the entire trench. The warning ribbon tape will provide a warning to anyone digging above the run that an electrical line exists below that.
8) The 20 amp branch circuits will require 12 AWG copper and the 15 amp circuits can use either 14 or 12 AWG copper conductors, type THHN rated.
10 AWG Copper is not required for the branch circuits.
Hope this helps………If you have any additional questions, let me know and I’ll be glad to answer them for you.
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