In some cases, sensitive equipment may be disturbed by the high frequency emissions that the lamp as a gas discharge device emits, even if operated at mains frequency. In these cases it sometimes helps to just swap the polarity. Care should be taken that the ballast is always connected to the phase and the lamp to the neutral as an earthed conductor, not vice versa. This reduces the likelihood of described trouble. If it still occurs, a so-called symmetric ballast may help, the inductance of which is split in two halves, each of them to be connected to one end of the tube (Fig. 3.2). Beyond, only the usual commonplace filters will help, whenever these, if used excessively, may cause a leakage current problem. Inrush currents, however, are generally not a problem with magnetic ballasts. Their inrush currents are not that high. Further attenuation can be achieved when serial compensation is applied (bottom of Fig. 2.1), while parallel compensation (chapter 4) adds the inrush current of the capacitor, which has very steep rise time edges and may therefore very well become a problem.
When talking about the harmonic disturbances of electronic ballasts it is frequently alleged that magnetic ballasts also cause current harmonics, while this is not really so. The ballast itself is a linear element if designed properly, so as not to let the core material enter the range of magnetic saturation under normal operating conditions, which would be highly disadvantageous from a power quality as well as an energy efficiency viewpoint. Rather, the non-linear behaviour of the lamp itself causes an extreme magnitude of voltage distortion (Fig. 2.7, Fig. 2.8) but which on account of the high inductance of the ballast causes only little current distortion. So no nameworthy disturbance appears across the terminals of the luminaire. The harmonic load on the neutral conductor with lamps spread equally across the three phases is correspondingly low, in the case of 58 W lamps the simulation reveals about 35% of the phase current (Fig. 3.3).