450. In order to definitively determine whether or not fuse «1», shown in the illustration is blown using an on-line testing technique, across what points would you connect the voltmeter leads

An online fuse test requires connecting a voltmeter between the load side of the suspect fuse and the line side of a known live phase to determine if the fuse is blown. Connecting the leads from the bottom of fuse 1 to the top of either fuse 2 or 3 achieves this, indicating a blown fuse with an abnormal voltage reading.