For what it's worth protecting a Feeder with a GFCI is not a great design.
The cumulative leakage current of all the branch circuits will likely lead to nuisance tripping of the feeder.
And this is a problem in Britain where an RCD (GFI) can protect an entire distribution panel or an entire installation, even though the trip current is 30mA rather than 4 to 6mA.
