Descripción de los electrodos de puesta a tierra según el Art. 250 del NEC, elaborado por Mike Holt para la revista EC&M
250 Ground Rod Electrodes
Nov. 21, 2013 Mike Holt|Electrical Construction and
Maintenance
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Q. What are the requirements related to the use of a ground rod
for the grounding electrode system, including sizing of the
grounding electrode conductor? (Answer based on 2011 NEC.)
A.Ground rod electrodes must not be less than 8 ft in length in
contact with the earth [250.53(G)]. Rod-type electrodes must have a
diameter of at least 5/8 in., unless listed [250.52(A)(5)(b)]. Rod,
pipe, or plate electrodes must meet the following requirements
[250.53(A)]:
1) If practicable, rod, pipe, and plate electrodes must be
embedded below the permanent moisture level and be free from
nonconductive coatings such as paint or enamel.
2) A single rod, pipe or plate electrode must be supplemented by
an additional electrode thats bonded to one of the following:
The single rod, pipe, or plate electrode
The grounding electrode conductor of the single electrode
The neutral service-entrance conductor
The nonflexible grounded service raceway
The service enclosure
Exception: If a single rod, pipe, or plate grounding electrode
has an earth contact resistance of 25 ohms or less, the
supplemental electrode isnt required.The grounding electrode
conductor, if its the sole connection to the ground rod, isnt
required to be larger than 6 AWG copper [250.66(A)]. In addition,
the diameter of a ground rod has an insignificant effect on the
contact resistance of a ground rod to the earth. However, larger
diameter ground rods ( in. and 1 in.) are sometimes installed where
mechanical strength is desired, or to compensate for the loss of
the electrodes metal due to corrosion.
