The National Electrical Code has some very specific rules and regulations about underground wiring methods and points of asttachment. This is a look at the highlights of the outdoor sections of the code.
- Install receptacles a minimum of 12" above grade. This keeps receptacles out of water and snow accumulations.
- Use either ground fault circuit interrupter (GFCI) receptacles or GFCI Breakers to protect the users of these receptacles.
- If more than four receptacles are connected to a circuit, a 20-amp circuit should be installed. Likewise, if an outdoor lighting load is to have more than one light fixture that exceeds 300 watts, be sure to use a 20-amp circuit to accomodate the load.
- Receptacles and switches mounted outdoors should be installed in weatherproof electrical boxes that incorporate weatherproof covers. It is advised to use bubble covers over receptacles that cover cords from the weather while they are plugged in.
- Call the underground utilities company hotline before digging. They come out and mark any underground osbtructions that may be in your path, giving you a heads-up on where to and not to dig.
- Type UF cable is to be used for direct burial wiring needs and is identified by its grey covering. Open wiring not protected in conduit should be buried at least 24" below the surface.
- Underground wiring run in plastic conduit must be buried at least 18" below the surface and in schedule 80 PVC. This is a more durable plastic conduit (grey colored) than its silimilar-looking water pipe that is a white or cream-colored piping.
- Receptacle boxes that are run out into the middle of a yard or where there is no anchoring point for the junction box, must have the schedule 80 PVC embedded in concrete to supprot the box. Another method, is to attach the box to a post that is either driven or buried in the ground. Receptacle boxes should be mounted at least 12" above grade but no more than 18" above grade for the unattached method.
- Be sure that overhead powerlines meet the minimum height clearance.