How about trying to protect downstream of a GFI receptacle when installed into a multi-wire circuit?
To do so would be a violation......even if it would work (which it wouldn't).
"300.13(B)
Device RemovalIn multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders,
receptacles, and so forth, where the removal of such devices would interrupt the continuity."
A pretty common failure becomes a nightmare on a MWBC when the neutral isn't pigtailed. A (often backstab) receptacle
removes itself from the circuit, opening the grounded conductor.
As always, improper installation is the culprit.
[This message has been edited by electure (edited 01-05-2007).]