I have a subpanel whose feed protected by two 30 amp old stlye (glass) fuses on each of the 120 volt lines.

In the subpanel is a 20 amp breaker for a pool pump.

The capacitor for the pool pump died and one of the 30 amp glass fuses blew.

My question is why didn't the 20 amp breaker trip before the 30 amp fuse blew?