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Comparison of IRC Section E3608 and NEC Sections 250.50 - 250.70
Overview
The IRC (International Residential Code) and NEC (National Electrical Code) both establish grounding electrode system requirements. However, since the IRC is derived from the NEC but streamlined for residential use, there are differences in structure, wording, and level of detail.The NEC is the authoritative source for electrical requirements, covering residential, commercial, and industrial applications. The IRC, on the other hand, simplifies these rules for residential inspectors, often condensing content and omitting provisions that are not strictly necessary for residential work.
Key Differences
1. Scope and Structure
- NEC 250.50-250.70 is highly detailed and applies to all buildings, including commercial and industrial structures.
- IRC E3608 is structured similarly but is streamlined for residential structures. It omits certain electrode types and advanced bonding requirements applicable to industrial settings.
2. Grounding Electrode System (250.50 vs. E3608.1)
- The core requirement is the same: all available electrodes must be bonded together to form a grounding electrode system.
- The IRC mirrors NEC 250.50 but simplifies wording.
- NEC includes 250.52(A)(8) (Other Local Metal Underground Systems), which the IRC omits.
- NEC specifies that if no electrodes are present, one must be installed from 250.52(A)(4)-(A)(8), while the IRC only lists (A)(3) through (A)(6).
3. Grounding Electrode Types (250.52 vs. E3608.1.1 - E3608.1.6)
- Both codes list acceptable electrodes, including metal water pipes, concrete-encased electrodes, ground rings, rods, pipes, and plates.
- IRC excludes "Metal In-Ground Support Structures" (NEC 250.52(A)(2)), which are used in industrial and commercial settings.
- NEC includes "Other Local Metal Underground Systems" (250.52(A)(8)), which the IRC does not.
4. Metal Underground Water Pipe (250.52(A)(1) vs. E3608.1.1)
- Both require at least 10 feet (3.0 m) of direct earth contact.
- IRC E3608.1.1.1 states that interior metal water piping beyond 5 feet (1.52 m) from entry cannot be used as an interconnection conductor. This matches NEC 250.68(C)(1).
- The NEC allows commercial and industrial buildings to use interior metal water piping beyond 5 feet if maintenance and supervision ensure safety (IRC does not allow this exception).
- NEC explicitly requires bonding around meters, filters, or similar devices to ensure continuity.
5. Concrete-Encased Electrode (250.52(A)(3) vs. E3608.1.2)
- Both require a minimum 20-foot (6.0 m) electrode, either rebar (½ inch) or 4 AWG copper.
- The NEC provides an Informational Note clarifying that concrete with vapor barriers or insulation is not considered in "direct contact" with the earth, but the IRC does not.
6. Ground Rings (250.52(A)(4) vs. E3608.1.3)
- Both require a minimum 20-foot (6.0 m) loop of bare copper conductor, at least 2 AWG.
7. Rod and Pipe Electrodes (250.52(A)(5) vs. E3608.1.4)
- Both require a minimum 8-foot (2.44 m) electrode.
- NEC 250.52(A)(5)(b) specifies that rod electrodes must be at least ⅝ inch in diameter unless listed, which the IRC adopts.
- NEC allows alternate installation methods when rock bottom is encountered (45-degree angle or burial in a trench). The IRC mirrors this but is more condensed.
8. Plate Electrodes (250.52(A)(7) vs. E3608.1.5)
- Both require a minimum surface area of 2 square feet (0.186 m²).
- Both require burial at least 30 inches (750 mm) deep.
9. Bonding Requirements (250.53 vs. E3608.2)
- Bonding jumper rules are nearly identical.
- The IRC specifically states that rebar cannot be used as a conductor to interconnect electrodes, which is also in NEC 250.53(C).
10. Supplemental Electrode Requirements (250.53(A)(2) vs. E3608.4)
- The NEC states that a single rod, pipe, or plate electrode must be supplemented unless it has a resistance of 25 ohms or less.
- The IRC includes the same requirement but words it differently.
- Both specify a 6-foot minimum spacing between multiple electrodes.
11. Aluminum and Gas Piping Restrictions (250.52(B) vs. E3608.5 & E3608.6)
- Both prohibit aluminum electrodes and underground metal gas piping as grounding electrodes.
12. Pool, Spa, and Hot Tub Structures (250.52(B)(3) vs. E3608.7)
- Both prohibit the use of pool, spa, and hot tub reinforcing steel as grounding electrodes.
Summary of Key Differences
| Topic | IRC E3608 | NEC 250.50-250.70 | Difference |
|---|---|---|---|
| Scope | Residential | All structures | NEC covers industrial & commercial applications |
| Electrode Bonding | Requires all present electrodes to be bonded | Same requirement but includes additional electrode types | NEC includes "Other Local Metal Underground Systems" |
| Metal Water Pipe | Cannot use interior piping beyond 5 feet | Allows usage in commercial buildings under supervision | IRC is stricter for residential applications |
| Concrete-Encased Electrodes | Requires 20 ft of rebar or 4 AWG copper | Same, but clarifies vapor barriers affect grounding | IRC does not mention vapor barriers |
| Rod and Pipe Electrodes | Requires 8 ft length | Same, but includes additional language on installation near rock | IRC is a condensed version |
| Other Local Metal Underground Systems | Not mentioned | Permitted under 250.52(A)(8) | NEC allows more electrode options |
| Bonding Jumpers | Rebar cannot be used as a bonding jumper | Same restriction | No difference |
| Supplemental Electrodes | 25-ohm rule applies | Same rule but better defined | No major difference |
| Gas Piping & Aluminum Electrodes | Not permitted | Not permitted | No difference |
Final Conclusion
The IRC E3608 is essentially a condensed and reorganized version of NEC 250.50-250.70, removing commercial/industrial-specific provisions while maintaining the core residential grounding requirements. The biggest differences are:- The NEC includes additional electrode types (metal in-ground support structures, other underground metal systems).
- The NEC allows some flexibility in industrial/commercial applications (such as using interior metal water piping beyond 5 feet).
- The IRC simplifies language and omits clarifications found in NEC Informational Notes (like the impact of vapor barriers).