Blown fuses in circuit adjacent to a faulted circuit

[EC Dan]

I'm stumped by this one, which is made worse by the fact that I'm not at the location (several states away) to trouble-shoot in person. We have a panel with a 5 HP VFD (CFW500) running a 2 HP three-phase blower, and two single-phase heating circuits controlled by SCRs. Heating circuit 1 is on legs A and B, heating circuit 2 is on legs B and C. Heating circuit 2 had a fault, which in addition to tripping it's own circuit breaker, blew the line fuses (JHL30) on legs A and C. We do not know if this was a L-L or L-G fault, and we can't detect evidence of the fault at the heater. These are proprietary heaters in a closed chamber with exposed energized surfaces and condensate build up, so the incidence of the fault is not exactly surprising, but the VFD line fuses being affected is surprising. After replacing the fuses, the drive works fine. My initial thought was that since the VFD is a regenerative type, it was dumping power back to the line side as it contributed to the fault in heating circuit 2, however after discussing this with the VFD vendor, it seems unlikely enough current would be generated to blow 30 A fuses (would have to be around 150 A to blow these fuses based on the TCC), and the VFD would likely be toast if it did pass that much. The heating chamber and blower motor are both grounded back to the panel ground bar, which also connects to the SCR controllers and VFD. Does anyone have experience with circuits tripping/blowing in circuits adjacent to faulted circuits?