Here’s the plan. You need to supply power to an out building, perhaps a moderate workshop separate from the house and you need at least a hundred amp electrical service panel. 100 amp panels can service up to eight 120 volt circuits. Each 240 circuit requires two slots. So with a hundred amp service you could run two 240 volt circuits and four 120 volt circuits. This is usually adequate for a small shop. For a shop up to a 100 ft away, voltage drop calculators can be used to determine wire size and you will want to keep your drop under 3 volts. Aluminum in far cheaper than copper but requires larger wire gauge, given a 100 foot run, 2/0 AWG aluminum wire you will experience a 2.46 voltage drop or a 1.03% drop. Your subpanel will have 237.54 volts available.
Underground Feeder Cable
Copper UF or underground feed is neither heavy enough nor economical. You have to run three aluminum 2/0 AWG with a #1 AWG ground. One pair is your hot lines, one a neutral and the other the ground. You can buy aluminum 3 wire with ground direct burial service entrance cable for under $2.50 per foot. Or you can use individual wires pulled through 2” conduit, preferably schedule 80 plastic. Even with the service cable you will need conduit in the transition from the trench bottom to the service panel, at both ends. Cable needs to be buried in sifted sand or soil. No rocks as these can cut through the sheathing. Also consider running phone and or network wire for internet access to the shop.
Wire a Lighting Circuit
You will need to install #6 AWG to service a 30 amp 220-240 volt circuit. All other circuits are 12 gauge AWG solid copper to power 110-120 circuits. It is suggested that the lighting circuit to be separate from line circuits. Another consideration for the shop is to install double duplex outlets, 4 receptacles per outlet will be appreciated in the shop environment. For lights, 48 inch LED light fixtures will last 20 years without changing a bulb, and use 1/3rd the power. The 240 circuits can power compressors and/or welders and perhaps even table saw if wired for 240 volts. You may want to contemplate three 30 amp 240 circuits; you will still have more than enough single 110-120-volt circuits for the typical shop. Better an extra than to come up short. And you may consider including one 50-amp 240 circuit. The high voltage circuit are generally limited to a single outlet. With a ground wire running to the main panel, the subpanel will be grounded as well back to the main. If grounded through the main the neutral and ground bars are not bonded. With a separate subpanel ground, the ground and neutral bars are bonded.
Electrical Wiring, Lighting & More in Laguna Woods, Santa Ana, Newport Beach, Huntington Beach, Laguna Beach, Aliso Viejo, Costa Mesa, Fountain Valley, Irvine, Lake Forest & Orange County, California
Electrical systems have a lot of variables, NEC (National Electrical Code) is recognized in all 50 states. But each state, county and municipality may have their own additions to the code. Sometimes even the experts disagree to best practices across jurisdictional boundaries. If in doubt it is best to consult an experienced electrician or hire the work out. You can hang the subpanel and even do the interior wiring and dig the trench, but correct installation is crucial for efficient, effective and safe installation.