Their intended purpose is to protect the utility distribution sytem, not to protect the transformer and its secondary conductors.
Don
To elaborate a bit on what Don said:
Larry, the cutouts are used to help
reduce the possibilty of violent failure of a faulted transformer/capacitor, to prevent the primary conductor burning down from a fault, to provide isolation of a faulted tx/cap/feeder; and to provide in most cases a visible means of locating a fault. (Most cutouts drop open or otherwise provide a visual cue that they've opened.)
The cutouts on a transformer are rarely fused to protect the transformer from overloads, even sustained ones. The utility practice is to allow the trans to operate to failure, usually no more than a burnout resulting in primary current in excess of the fuse cutout rating, which then opens. But sometimes the short circuit current available on the primary is very high, or the fuse rating is accidently too high, then the transformer can fail anyway by explosion or fire.
That's why faults like this one and some others we've seen here can happen without taking out a primary fuse/cutout.
[This message has been edited by mxslick (edited 09-18-2006).]