In several models of dielectric breakdown, nondestructive electric breakdowns precede destructive thermal dielectric breakdown. Both processes in oxides between 5 nm and 80 nm thick have been studied. The two breakdown phenomena have been differentiated, and the electric breakdowns have been separated from the dielectric breakdown. During constant voltage stressings, prior to dielectric breakdown, transient voltage spikes were measured and spots formed on the surface of the wafers due to electric breakdowns. Similar transient spikes occurred when measuring ramped breakdown voltages. It was found that the time dependent dielectric breakdown (TDDB) distributions measured on a series of identical oxides at the same voltages depended on the resistance and capacitance of the measurement test equipment due to the thermal nature of the dielectric breakdown. The TDDB distributions were shifted to shorter times if (i) the impedance of the test equipment was lowered and/or (ii) the capacitance of the test equipment was raised. The implications of this work are discussed in terms of electric and dielectric breakdown models and practical circuit and device operation.