The ground fault current will remain close to the same for 'normal' or isolated phase installations.
Either way there will be a full size EGC in each raceway and either way all conductors connected to the effected phase will contribute to the fault current.
Well ok your saying in any case or condition isolated paralleled conductors will trip a differential current relay and resistance doesnt play a part .
What if i had a floating neutral ?
A delta secondary feeding a motor load 3 phase and it grounded out one phase to case of motor and the breaker held for weeks ?
And the motor control center was isolated parallel fed no neutral just a ground .
What iam saying is when you have a ground fault the grounding conductor doesnt always take the fault there are other paths and the neutral return is also one of them and worst condition would be a one conductor in a group of paralleled conductors in a isolated arrangement .
This would make contact in circuit a resistance loop is now from that point to the grounding point and never trip the differential relay until it was too late .
The grounding conductor is for a much high trip current the single conductor cant take that under a condition of time and trip the minor fault now becomes a major fault .
High resistance will not trip a breaker fault or no fault but isolated paralleled conductors can present lots of other conditions you dont have with a mixed group of conductors .
If you have ever work a data center or a power plant you are not going to install a isolated run of paralleled conductors and what i just stated above was from a Black & Vech electrical engineer he said dont put all you eggs in the same basket its a EMI nite mare in a data center .
And in a Power Plant its a down time under a critical outage if you can run your load with less but not with all conductors lost.
Thats why they dont like paralled isolated runs .