Arcs are operated in noble gases with sinusoidal and switched dc currents of different frequencies in a model lamp between tungsten electrodes with properties appropriate for high intensity discharge lamps. The sum of the cathode and anode fall, called electrode sheath voltage ESV(t) = u_c(t) + u_a(t), is determined by a variation of the arc length and the anode fall u_a(t) by probe measurements along the arc axis and an extrapolation procedure. It is found that u_a(t) adopts low, approximately constant values within a half cycle. Therefore the time variation of the ESV reflects that of u_c. It was observed by high speed photography that a high value of u_c after current zero crossing (CZC) may initiate a transition of the initially diffuse mode of cathodic arc attachment into a spot mode. It is accompanied by a breakdown of u_c causing the formation of a voltage peak starting at current zero crossing. It is a prominent example of the so-called commutation peak (CP). By an adjustment of the operation conditions to a low u_c the cathodic arc attachment remains diffuse during the whole half-cycle. It is also indicated by high speed photography that the arc constriction in front of the anode is relieved with increasing operation frequency. It is illustrated by measurements that commutation peaks may be removed by an increase in the arc current, a decrease in the electrode cooling, a reduction of the filling gas pressure and an increase in the operation frequency. Moreover it is demonstrated, that the formation of a CP is sensitively dependent on the electrode surface structure.