Electrical wiring and conduits have certain rules for how they are buried and how deep by the National Electrical Code, used by all the cities in the USA. The smallest ditch is 6 inches TO THE TOP OF THE PIPE. Electricians get confused on this and think the ditch can be just 6 inches. You have to account for the pipe size too. A small pipe adds 1 inch and has to have a ditch 7 inches deep. Larger pipes can add 2-6 inches. To qualify for a 6 inch depth of electrical conduit, rigid steel metal conduit that threads together must be used. The problem with this type of pipe is that in about 25 years, it rusts out completely and the wires are left in the dirt rotting.
The 2nd level, which is used 99% of the time in all electrical installations is 18 inches deep TO THE TOP OF THE PIPE. The pipe is gray PVC conduit and will last forever buried underground.
The 3rd level is when using UF (underground feeder cable) which is flat and gray wiring with a very thick coating. Very expensive too, plus you have to install it 24 inches deep and protect it from 18 inches upward above ground in a conduit so it will not get damaged.
