Was this the way it was drawn on the single line diagrams, or elsewhere in the Engineered planset [to use paralleled grounded conductors that are smaller than 1/0]??
wonder how that got through plancheck
Must have been the last day before Vacation - both times!
If this is not the way it was drawn up, then it's somebody's conception of an increased ampacity for the grounded conductor [200% of unbalanced load size].
Technically, it shouldn't be an immediate hazard, but it's not within the minimum requirements of the NEC, so that alone makes it something of consern.
I can see a possible change in the future NEC, as to this type of situation. This one wouldn't really have the expected calamity of a typical paralleled feeder. In this case, the ungrounded feeders [subfeed] would be sized correctly [we hope], using only single conductors. The grounded conductor is being supplimented with an additional conductor of equal size, to make the end result ampacity 200% of any single ungrounded conductor.
In other setups, the total amperage is paralleled across the individual feeders, and is protected by an OCPD that exceeds the ampacity of a single conductor by at least 100%.
Here I can see the need to use conductors of 1/0 or larger for overall integrety and strength.
The grounded conductor being supplimented is to cover the highest possible load on that conductor, which exceeds the ampacity of a single conductor. As long as the terminations are solid, the conductors are equal in size, length and type, and the feeder is derated properly for the 5 current carrying conductors - it really doesn't pose any danger as far as I can see. Others may not agree with me, so please post any comments.
I would not say the same if 4 smaller conductors were used to equal the 200% rating of a given ungrounded conductor. That's going back to paralleled conductors, instead of supplimented conductors.