I live in Geauga county Ohio. My question is three part. First what type of wire do I need to run from the house underground to a post lamp 100 feet away? Second,does it need to be in conduit and thirdly, how deep does it need to be?
According to NEC table 300.5, for using a branch circuit of 120V and not more than 20A, with GFCI protection:
- If it's under 2" thick concrete or equivalent, then depth = 6" and you can use direct burial-rated -- i.e. type UF -- cable, or run in a conduit
- Under a driveway (for 1-2 family homes), depth = 12"
- Under lawns (and anywhere except streets, buildings, parking lots), depth = 12" for direct burial-rated cable, or 6" in a metallic conduit
You will need to get weatherproof cabling like this - (UK site but used for illustrative purposes only). It's got heavier duty covering to withstand small rocks etc.
Laying it in conduit would probably make it easier to lay and find again should you need to. Conduit will also help guard against accidentally cutting the cable when gardening (should you ever need to dig a deep enough hole).
However, double check the rules and regulations locally - ask your local building inspectorate. They should be able to tell you if there are minimum depth regulations too.