Codes, Standards, and Reference Documents
Codes, Standards, and Reference Documents
This domain tests which document governs a test, how the NEC sets minimum installation rules, and how NETA ATS/ATO and IEEE standards define test methods and intervals.
Core rules
- NFPA 70 (NEC) is installation code; NETA ATS covers acceptance testing; NETA ATO covers maintenance testing; IEEE standards give test methods and interpretation.
- NEC 110.26 working space; 250.66 grounding electrode conductor; 250.122 equipment grounding conductor; Article 430 motors; Article 450 transformers.
- Manufacturer instructions and project specifications can be stricter than the NEC; follow the most stringent applicable requirement.
- Use the correct table: GEC size is based on service-entrance conductor size, not overcurrent device rating.
Worked example
A 400 A service uses 3/0 Cu service-entrance conductors. Table 250.66 requires a 4 AWG Cu grounding electrode conductor. The reasoning: 250.66 is keyed to the largest service conductor (3/0 Cu falls in the 2/0-3/0 row), not to the 400 A breaker. Sizing from Table 250.122 would be wrong because that table is for equipment grounding conductors.
Traps
- Using the EGC table for the GEC.
- Applying ATS acceptance limits to maintenance tests.
- Ignoring local amendments or the project specification.
- Citing a standard without the edition or test section.