Washington State has a burial depth and protection requirement for the GEC. It was published in the Nov 2011 Electrical Currents, and that document is considered enforceable as the interpretation of the Chief Electrical Inspector. I always recommend Washington electricians subscribe to the Electrical Currents, sign up here:
http://www.lni.wa.gov/Main/Listservs/Electrical.asp. Back issues of the EC are available at that web site.
The NEC has never required a burial depth requirement for the GEC
Here is the requirement
Inspectors have been encountering grounding electrode installations that are subject to physical damage. NEC
250.64(B) has specific requirements for protection of exposed grounding electrode conductors.
Exposed grounding electrode conductors:
? Smaller than 6 AWG must always have physical protection.
? Sized 6 AWG that are free from exposure to physical damage are permitted to run along the surface of
the building construction without protection where it is securely fastened to the building surface.
? Sized 4 AWG or larger must be protected where exposed to physical damage. This requirement was
changed from ?severe? physical damage in the 2005 NEC.
Physical damage is not defined in the NEC. The department?s electrical inspectors will consider the grounding
electrode conductor to not be exposed to physical damage when:
? The conductor is buried more than 12? deep in the earth outside the building?s footprint.
? Encased or covered by 2? of concrete or asphalt.
? The conductor is inside the building footprint and protected by the building?s structural elements or when
inside and determined, by the inspector, to not be subject to physical damage.
? Enclosed by a metal or nonmetallic raceway or enclosure. The raceway or enclosure must be approved to
protect from severe physical damage if it is not protected by appropriate physical barriers from contact
with vehicles, lawn mowers, and other equipment that might damage the conductor or enclosure.
If ferrous metal raceways or enclosures are used to protect the conductor, they must be bonded at both ends to
the conductor according to the requirements in NEC 250.64(E).
Problems with physical protection may be avoided by using grounding electrodes that do not require
supplemental electrodes or where the grounding electrode conductor can be installed solely inside the structure
of the building (e.g. concrete-encased electrode, exterior metal underground water pipe with 10? or more of the
pipe in direct contact with the earth, etc.).
Tom, Electrical Instructor in Washington State.
