Stumped by the Code? Installing a Grounding Electrode Using Ground Rods
All questions and answers are based on the 2017 NEC.
Q. What does the Code require in regard to installing a grounding electrode using ground rods?
A. Grounding electrode system installation requirements are outlined in Sec. 250.53.
(A) Rod electrodes
(1) Below permanent moisture level. If practicable, pipe electrodes must be embedded below the permanent moisture level and be free from nonconductive coatings such as paint or enamel.
(2) Supplemental electrode. A rod electrode must be supplemented by an additional electrode that’s bonded to:
(1) Another rod electrode
(2) The grounding electrode conductor
(3) The service neutral conductor
(4) A nonflexible metal service raceway
(5) The service disconnect
Exception: A single rod electrode having a contact resistance to the earth of 25 ohms or less isn’t required to have a supplemental electrode.
Author’s comment: Generally, a single ground rod won’t have a contact resistance to earth of 25 ohms or less. In many cases, a ground rod with a supplemental electrode (two rod electrodes) won’t have a contact resistance to earth of 25 ohms or less. However, the maximum number of rod electrodes required by the NEC is two regardless of the contact resistance.
(3) Spacing. The supplemental electrode for a rod electrode must be installed not less than 6 ft from the rod electrode.
(B) Electrode spacing. Electrodes for premises systems must be located no closer than 6 ft from lightning protection system grounding electrodes. Two or more grounding electrodes that are bonded together are considered a single grounding electrode system (Figure).
(C) Grounding electrode bonding jumper. Grounding electrode bonding jumpers must be copper when within 18 in. of the earth [250.64(A)], be securely fastened to the surface, and be protected from physical damage [250.64(B)]. The bonding jumper to each electrode must be sized in accordance with 250.66.
Author’s comment: The grounding electrode bonding jumpers must terminate by any of the following means in accordance with Sec. 250.8(A):
- Listed pressure connectors
- Terminal bars
- Pressure connectors listed as grounding and bonding equipment
- Exothermic welding
- Machine screw-type fasteners that engage not less than two threads or are secured with a nut
- Thread-forming machine screws that engage not less than two threads in the enclosure
- Connections that are part of a listed assembly
- Other listed means
When the termination is encased in concrete or buried, the termination fittings must be listed for this purpose [250.70].
These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code
