Ok, so that brings me to a (hopefully) final question on this topic. If there are multiple parallel conductors spread across multiple conduits, how does one size the EGC in each conduit? Must each EGC in each conduit be full-sized based on the rating of the OCPD? Or does each EGC in each conduit get sized to the capacity of the current carrying conductors in that conduit, provided that the sum of the capacity of all EGCs in all conduits matches the rating of the OCPD?
The reason I'm asking is this:
We have service entrance conductors from a 3-phase, 480V, 1,200 amp service panel to a distribution panel. The conductors run through four buried 4" PVC conduit. Each conduit contains four 500 mcm aluminum conductors (one for each of the three phases, plus one neutral) and one 1/0 aluminum EGC. So there are a total of sixteen current-carrying conductors and four EGCs.
We are trying to free up two conduits to run some additional conductors. By my calculations, running eight 500 mcm aluminum conductors plus two 1/0 aluminum EGCs in one 4" PVC conduit will put us at 40.32% fill. If we can consolidate the two EGCs into one, that may allow us to stay below 40%, but it will depend on the required size of the EGC.
(We are trying to avoid the expense of discarding our existing 500 mcm aluminum conductors and replacing with 350 mcm copper.)