Electrical Installation Depths are different depending on which type of conduit or cable one uses for the application. As you can see from the photo, if one is using Rigid Metal Conduit that is very thick and screwed together in 10ft lengths, it only has to be buried 6 inches. The reason is that anyone digging with a shovel can cause damage to it or the wiring. The problem is that over 15-20 years, the Rigid Metal Conduit rusts and rots out. The 2nd application would be using PVC Conduit. PVC will last forever underground and has to be buried deeper than Rigid Metal Conduit. The last is Direct Burial UF (Underground Feeder) Cable that can be laid in a ditch 24 inches deep and is very safe at that depth.
