In this section of the JLC Field Guide, we address what is often called the load center or just the electrical panel, including the service entrance that feeds into, and any subpanels that might feed off of, the main panel.
A modern residential overhead service entrance comprises three cables — two hot and one neutral — that run from the utility lines to a point of attachment at the weather head, and then down an entrance cable or conduit to the meter socket. In this type of system, the utility company’s equipment ends at the point of attachment on the house. Older systems may have different configurations (below).
Figure: Evaluating an Overhead Service Entrance
The service entrance may run overhead or underground. For either type of entrance, check with the local electric utility for its requirements. Be sure to seal the exterior wall penetration at the service entrance with an approved fitting and/or sealing compound. Water leaks at the service entrance can lead to corrosion of electrical components at the main panel.
Overhead service entrance cables must be higher than 10 ft. above walking surfaces, including a deck or porch. As of the 1999 NEC, this 10-ft. clearance must be maintained at least 3 ft. out from a porch or deck in every direction, including around corners (below).
Figure: Overhead Service Clearance
An underground service cable may be either directly buried or encased in conduit. If in conduit, the raceway must be sized adequately for the conductors that it is carrying. With an underground service, the underground equipment typically belongs to the owner and must be connected to the utility company’s pole or pad-mounted transformer.
For information on running a temporary service during construction, click here.