250.66(A) Size of Alternating-Current Grounding Electrode Conductor. Connections to a Rod, Pipe, or Plate Electrode(s).
Code Change Summary: A revision was made to clarify that a grounding electrode conductor to a ground rod, pipe or plate is never required to be larger than 6 AWG copper or 4 AWG aluminum.
The previous code language seemed pretty clear before but for some reason, many people were still confused by the wording.
A grounding electrode conductor (GEC) from an electrical service to a ground rod, pipe or plate type electrode is never required to be larger than 6 AWG copper or 4 AWG aluminum unless the GEC continues on from the rod, pipe or plate to another electrode that may require a larger GEC such as a concrete encased electrode, building steel or metal underground water pipe that qualifies as a grounding electrode.
The minimum size GEC permitted to connect a concrete encased electrode is 4 AWG copper. Building steel and metal underground water piping that qualifies as a grounding electrode may require a larger GEC since the GEC to these electrodes is sized based on the size of the service entrance conductors and table 250.66.
If the GEC starts at the service and goes to a ground rod or group of ground rods and stops there, the GEC is never required to be larger than 6 AWG copper or 4 AWG aluminum. If the GEC continues from the rod to another electrode of a different type that requires a larger GEC, then the GEC from the service to the first rod will be under sized.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2011 Code Language:
250.66(A) Connections to Rod, Pipe, or Plate Electrodes.
Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5) or (A)(7), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
2014 Code Language:
250.66(A) Connections to Rod, Pipe, or Plate Electrode(s).
Where the grounding electrode conductor is connected to a single or multiple rod, pipe, or plate electrode(s), or any combination thereof, as permitted in 250.52(A)(5) or (A)(7), that portion of the conductor that is the sole connection to the grounding electrode(s) shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.