Grounding, Bonding, and Electrical Protection
Core concepts
Grounding and bonding are distinct: grounding establishes a reference to earth; bonding connects metal parts to equalize potential. Know the service grounding electrode system, equipment grounding conductors, and the bonding of metal water piping, structural steel, and gas piping (bonded, not used as an electrode). Understand why low voltage systems are bonded at one point only to prevent ground loops, and how shielded cable shields are terminated. Learn overcurrent protection basics: fuse and breaker types, interrupt rating, series ratings, and the difference between overload and short circuit. Surge protection devices belong at service and at sensitive equipment.
Traps to expect
A frequent trap is treating a grounded conductor as an equipment grounding conductor, or bonding a low voltage system at multiple points. Questions may ask whether a separate grounding electrode is required for a subpanel (generally no; the equipment grounding conductor is run with the feeder). Another trap is confusing ground fault protection with arc fault protection, or assuming a surge suppressor replaces proper bonding.
Worked example
A CCTV head-end rack shows 0.8 V AC between the rack chassis and the building ground. Diagnose by checking whether the coax shields and the rack are bonded at more than one point. Correct approach: bond the rack to the building grounding system with a single low-impedance conductor, terminate shields at one end where the design permits, and verify continuity. Rule of thumb: one bond point per system to earth; many bonds among metal parts to equalize potential.