DO160D/ED14D S 22 describes procedures for pin testing; they define a specific source impedance for the transient generator. This inevitably limits the maximum current that can be driven into a pin during a test. Sometimes this implied current limit has been questioned as being too high since s/c currents associated with Waveform 5A have a lot of energy and can damage components. This paper reports investigations into actual current levels that can occur particularly when transorbs installed for protection purposes become conducting. Theoretical estimates and results of experiments are described. For Waveforms 4 and 5, the currents can be estimated for simple circuit equations. In some circumstances the current limits could be set too low so the procedures need to be carefully reconsidered during DO160D testing.