EGC sizing for Grounded Systems of ungrounded conductors, multiconductor cable, multiple circuits, and conductors in parallel when installed in conduits or Cable Trays shall comply with NEC Section 250.122 (A), (B), (C), and (F), and Section 392.60. The following conclusion is limited to installations affected by the length of the circuit run, and environment temperature for proper circuit operation (i.e. voltage drop).
Minimum size of EGC is selected from Table 250.122 based on the rating of the OCPDs. If ungrounded circuit conductors are increased in size, the EGCs must be increased proportionately. (Section 250.122(B)).
For grounded systems, the required EGC shall be one or more or a combination of a Wire-Type, RMC, EMT or grounded Cable Tray, and they shall be capable of carrying the imposed ground-fault back to the electrical supply source. (Section 250.122(A)).
For multiple circuits installation within raceway or cable tray, the EGC shall be sized based on the largest OCPD protecting the conductors, and for cable tray only the single conductor EGC shall be #4 AWG minimum. (Section 250.122(C)).
(Section 250.122(F)) For parallel circuit installation with raceways, cables or in cable tray, the EGC shall be installed in each parallel circuit. When parallel circuits are installed within the same raceway, cables or cable tray, a single EGC is permitted. Parallel conductors are permitted to be electrically joined at both ends for sizes #1/0 AWG and larger. Parallel conductors shall have the same number of conductors and electrical characteristics within one specific phase. Each Current carrying conductors installed in raceways, or not installed in raceways without maintaining spacing for length longer than 24”, the ampacity shall be reduced as shown in Table 310.15(B)(3)(a) and it shall apply only to power and lighting conductors. For cable tray only the minimum single conductor EGC shall be #4 AWG.
Parallel equipment bonding conductors shall be sized per Section 250.122, and for multiconductor with sectioned EGC smaller than #1/0 AWG is permitted as long as the combined circular mil complies with Section 250.122. Size Parallel bonding and supply bonding jumpers shall comply with Section 250.102.
(Section 392.60(A), (B), &(C), & 250.96(A)) Metal raceways and cable trays serving as EGCs, with or without the use of supplementary EGCs, must be maintained and serviced by qualified personnel, and they shall be bonded to enclosures, frames, fittings, and other metal non–current-carrying parts that are to serve as EGCs. Steel and Aluminum Cable Tray used as EGC must have all sections and fittings be identified as EGC, and marked with total cross sectional area to comply with minimum area as per Table 392.60(A). Bonding jumper size must comply with Table 250.102(C)(1), and it can be installed inside or outside of the cable tray, raceway or enclosure.