Grounding, Bonding, Overcurrent Protection, and Special Occupancies
Grounding, bonding, overcurrent protection, and special occupancies
Article 250 distinguishes the grounded conductor (neutral), the equipment grounding conductor (EGC), the grounding electrode conductor (GEC), and bonding jumpers. Service equipment must have a main bonding jumper and a grounded-conductor-to-grounding-electrode connection; downstream panels must keep neutral and ground separate except where specifically permitted. The GEC is generally sized from Table 250.66 using the service conductor size, while the EGC is sized from Table 250.122 using the overcurrent device rating. Article 240 governs overcurrent protection, standard ratings, small-conductor rules, tap rules, and series-rated assemblies. Chapter 5 adds special occupancies such as pools (Article 680), emergency systems (700), and interconnected sources (705).
Traps and a worked example
Traps include sizing the GEC from the breaker rating instead of the service conductors, bonding the neutral to ground in a subpanel, using a GFCI as a substitute for equipment grounding, and forgetting that an upsized conductor may require an upsized EGC under 250.122(B). In special occupancies, pool bonding and GFCI requirements are frequently tested, as are rapid shutdown for PV systems and separation of emergency circuits.
Worked example: a 200 A service uses 2/0 AWG copper service conductors. Table 250.66 gives a 4 AWG copper GEC for 2/0 copper service conductors. The 200 A breaker does not set the GEC size; the service conductor does. By contrast, a 200 A circuit’s EGC is sized from Table 250.122, which gives 6 AWG copper. Rule of thumb: GEC follows service conductors; EGC follows the overcurrent device.