The "Dummy Fuses" referenced in Electure's posted Hyperlink, are useful in 3 Pole Safety Switches; where the System used is a 3 Phase 3 Wire Corner Grounded Delta.
This effectively opens all 3 Conductors (both Ungrounded Conductors and the Grounded Conductor) simultaneously, and keeps the Grounded Conductor "Solid" (No OCPD in Series) at the Disconnect / Safety Switch.
Footnote: When such an item is seen by "4 Wire Wye-Guys only", the reactions by those unfamiliar with Corner Grounded Systems range from a simple "Whaddaheck???" to "Evacuate The Building!!!"
After which comes the difficulty of trying to explain why the Identified (i.e. Grounded) Conductor is One of the Three Wires for this 3 Phase 3 Wire Branch Circuit - and why White or Gray Insulation / Tape on this Conductor is Code Compliant...
Most grasp the concept and accept the System's "Differences", while only a few (be they obnoxious, arrogant, or simply from Mule-Level Reluctance), refuse to accept any part of such an Alien System's use, operation and Code Compliance. (Note: I mention the latter, due to a few ugly debates from past installations...)
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
The corner grounded systems I saw, (all sewer lift pumps) used equipment like single phase with two ungrounded conductors in a 2 pole breaker and a white grounded conductor with no overcurrent protection or disconnecting means at all. If there was a switch type disconnect, it was 2 pole.
I admit, the first one I saw, standing there all alone with no help around had me pretty confused for a minute I am glad I had heard of corner delta and was glad I figured it out before I said something dumb.