Grounding, Bonding, and Overcurrent Protection
Grounding versus bonding
Grounding connects the electrical system to earth; bonding ties metal parts together so they remain at equal potential and create an effective fault-return path. Know the conductors by name: grounded conductor (neutral), grounding electrode conductor (GEC), equipment grounding conductor (EGC), main bonding jumper, and bonding jumpers. The grounded conductor is connected to ground at the service (250.24) and at separately derived systems (250.30) only - downstream panelboards keep neutrals and grounds on separate bars.
250.50 requires all available electrodes to be bonded into a single electrode system: metal water pipe with 10 ft or more in contact (supplemented by another electrode), metal building frame, concrete-encased electrode, ground ring, and rod or pipe electrodes. A single rod must be supplemented unless it proves 25 ohms or less (250.53). GEC sizing comes from Table 250.66 and depends on the service conductor; EGC sizing comes from Table 250.122 and depends on the overcurrent device rating, not the conductor.
Overcurrent protection
Article 240 protects conductors. 240.4(D) caps 14 AWG at 15 A, 12 AWG at 20 A, and 10 AWG at 30 A. 240.4(B) permits the next higher standard device in defined cases, and 240.6 lists the standard ratings. 240.21 governs taps, and 240.92 covers supervised industrial installations. Distinguish overload (sustained excess current) from short circuit and ground fault, and remember that a breaker's job includes protecting the conductor, not just the load.
Worked example: a 200 A service with 2/0 Cu service conductors takes a 4 AWG Cu grounding electrode conductor (Table 250.66); a 200 A feeder takes a 6 AWG Cu equipment grounding conductor (Table 250.122).