Grounding: connected to earth
Bonding: things are connected together (doesn’t imply connection to earth)
Article 250 – 10 parts; must understand part 2 system grounding, and part 6 equipment grounding.
System Grounding part 2: intentionally connect one current carrying conductor to ground. Think of neutral on A/C system; the neutral conductor is connected to ground.
Equipment Grounding part 6: like the branches of a tree; all non-current carrying parts of an electrical system to ground (equipment, metal enclosures, conduit, rails [all have equipment grounding conductor EGC])
When equipment is bonded, and then grounded (connected to earth) there is no voltage potential between the equipment, and therefore no shock hazard.
For racking systems, although it may be feasible to construct your own, it’s a risk and often better off to buy UL 2703 listed racks. In this way you remove risk from your installation improve compliance with NEC.
NEC 690 part 5 (for PV) can modify requirements – 690.43 (D) modifies 250.97 requirement.
NEC 250.97 for bonding metal raceways, connected to metal enclosure; if enclosure has concentric or eccentric knockouts, you need a raceway bonding device such as bonding bushing; since these knockouts might not provide a sufficient bond. However, NEC 690.43 (D) modifies this requirement and states this only applies to solidly grounded PV system circuits greater than 250 V to ground.
Nowadays very few PV systems are solidly grounded – most modern installs are functionally grounded. So this modifications means additional bonding bushings aren’t required for nearly all PV system DC circuits. However these bonding bushings would still be required on 3 phase systems on 480 3 phase system ; where we have 277 volts to ground; from line to ground.