I want to put in two pedestal lamps at the beginning of my driveway, as well as a weatherproof outlet box. The total run from the outside panel is 30 ft. I want at least 30 amperes at the box. The wires will be in conduit.
Presently I have enough AL #6 wire for my hot & neutral (I already had the wire), but not enough for the ground. I do have some CU #10. Can I use it?
Best Answer
You can use the 10AWG copper for your EGC, provided the conductor is bare or insulated with a green or green + yellow stripes finish -- 250.118(A) doesn't say anything about not being able to use a grounding conductor made from a different metal than your circuit conductors:
and Table 250.122 allows the use of 10AWG copper for the EGC of all circuits up to 60A in ampacity. Since Table 310.15(B)(16) limits the ampacity of 6AWG aluminum THWN to 50A when in conduit, you'll be safe on that front.
HOWEVER, you must use receptacles of appropriate ampacity -- 15A receptacles are NOT allowed on 30 or 50A circuits! This restriction comes from 210.21(B)(3) and the associated Table:
Furthermore, you cannot run lighting in a dwelling unit occupancy off a 30A circuit -- this is prohibited by 210.23(B):
You'd need to install a weatherproof subpanel by your driveway with the 6AWG Al as a feeder to do this, following 312.2 for the enclosure:
Once that subpanel is in place, you could then use 14/2 w/ ground UF or USE cable rated for direct burial to run standard 15A branch circuits to the outlet box and light fixtures.
Either that, or just pull a bunch of THWN copper through the conduit (ensuring it's appropriately sized, of course), and run multiple branch circuits. You'll need at least 2 in this approach -- 1 15A for the lighting, and another branch circuit of the appropriate size to feed your outlets.