  We show the results of two-terminal and four-terminal transport measurements
on few-layer NbSe$_2$ devices at large current bias. In all the samples
measured, transport characteristics at high bias are dominated by a series of
resistance jumps due to nucleation of phase slip lines, the two dimensional
analogue of phase slip centers. In point contact devices the relatively simple
and homogeneous geometry enables a quantitative comparison with the model of
Skocpol, Beasley and Tinkham. In extended crystals the nucleation of a single
phase slip line can be induced by mechanical stress of a region whose width is
comparable to the charge imbalance equilibration length.
