Power transmission lines bring power from a generating station to an electrical substation. Power distribution lines bring power from the substation to customer homes. Transmission and distribution lines can be either overhead or underground.
Power transmission lines
Magnetic fields created by transmission lines vary with power line design, and how much electricity flows through the lines. However, at the edge of rights-of-way near 220 kV and 500 kV transmission lines, magnetic field levels in the 20-30 mG range can often be found. At a distance of 300 feet during average electricity demand, the magnetic fields from many transmission lines can be similar to typical background levels found in most homes.
Power distribution lines
Typical voltages for power distribution lines in SCE’s service territory range from 4 to 33 kV. Similar to transmission lines, the magnetic fields near distribution lines vary with power flow and design. According to the NIEHS, magnetic fields under main feeder distribution lines or over underground lines can create fields around 10 to 20 mG. For smaller distribution lines, field levels are often much less (below 10 mG to under 1 mG). At a distance of 100 feet, the magnetic field levels from distribution lines often drop to values similar to levels found in most homes.