For the 2003 UL White Book in pdf, see Joe T's first link at
https://www.electrical-contractor.net/ubb/Forum1/HTML/003428.html {~2MB}
Maint'guy, as I understand the situation, some ground faults on delta systems can require one breaker pole or one fuse to operate, where the voltage across the opening pole may be at line-to-line potential, causing failure in a underrated overcurrent device.
In a 120/240V 3-wire or 208Y/120 system, this condition cannot occur, so "slash-rated" breakers are not a misapplication. The ‘single-pole’ rating for ungrounded, corner-grounded or 4-wire delta 240 and 480V systems are subject to the “no slash” mandate.
The fuse side of this for 240V-delta systems—150V fuses are a misapplication, but OK for 208Y/120V service—as are 300V fuses OK for a 480Y/277V systems, but not in a 480V-delta system.
The short version of all this is that underrated overcurrent devices may delflagrate trying to interrupt a fault or overload.
[This message has been edited by Bjarney (edited 11-14-2004).]
