This page deals with high-voltage underground cables. Underground cables at lower voltages are covered in the pages on distribution.
4% of the high-voltage electricity network in England and Wales is underground, mainly in urban areas or areas of great scenic beauty.
With underground cables the individual conductors, being insulated, can be closer together, leading to greater cancellation and lower fields. However, unless they are buried very deeply, they can also be approached more closely, leading to higher fields. Overall, ground-level magnetic fields from underground cables fall much more rapidly with distance than those from a corresponding overhead line, but can actually be higher at small distances from the cable.
The graph shows an illustration of this for one particular underground cable and the equivalent overhead line.