If two different metals are immersed in an electrolyte, a voltage is generated between them which is greater the further apart the metals are in the voltage series (excerpt): (-) aluminum – zinc – iron – nickel – tin – lead – hydrogen (+/-0) – copper – silver – gold (+). In the presence of an electrolyte, a current flows in the closed circuit, which decomposes the electrolyte and causes metal ions to flow to the more negative pole (cathode), which is further to the left in the voltage series. The donor (anode) is always the positive pole, which is removed in the process. In practice, especially in the case of transitions from aluminum conductors to copper conductors, it is important to ensure that the contact point is not exposed to any electrolyte, even if it is only moist air. For this purpose, intermediate layers of cupal sheet are used, which consists of firmly rolled copper and aluminum sheet. In systems with direct current, it is advisable to ground the positive pole so that contacts and connections are always negative (cathode) with respect to the environment. In automotive technology, this is reversed for historical reasons. The negative pole is at ground potential here because it was previously assumed that the current flows from negative to positive (technical direction of current).

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