Short description of the problem.
Galvanic corrosion is an electrochemical reaction between two or more different or dissimilar metals. Dissimilar means that in order to start the reaction, one of the metals has to be chemically more active (or less stable) than the other(s). When we speak about galvanic corrosion, we have in mind the exchange of electric energy. All metals have electric potential because all atoms have electrons. The movement of these electrons is what we call electric energy. The galvanic corrosion of more reactive metal begins when two or more components from different metals, that have the mutual contact (because of the regular contact or the conductor) are placed in a liquid which conducts electricity (electrolyte). Anything, except chemically pure water, can become electrolyte. Not only sea water, but also ordinary tap water is a perfect electrolyte because of mineral substances, and with increasing temperature its electrical conductivity grows even more (this is the reason why the hulls of ship that are exploited in hot climate are prone to greater corrosion than the ones in northern seas). The same principle applies to bathrooms and towel warmers that are installed in them. Initiators of variable electric currents can be not only external, but also internal sources, such as short-circuit in the network, poor wire isolation, wet contact or incorrect connection of some of the elements of electric equipment.
There have been cases when 4B potential difference occurred in the bathroom. Theoretically, if construction is performed correctly, there should be no such thing. But practice and theory usually pass each other. Sometimes welded connection is replaced with stranding, thus creating additional resistance. Due to this, the potential difference occurs in different ends or floors of the pipe, which in the end leads to electrochemical corrosion. Electrochemical corrosion is especially aggressive to underground communications that are installed in primers of different acidity level, or if there are trains or trams nearby.
The corrosion problem or water mixers and towel warmers consists precisely of the fact that plastic pipes are suitable for them. Stand, of course, is made of metal pipes. All metal pipes are grounded: in newly-built houses it is done through the potential equalization system, and in old houses it is done through the grounding circuit in the basement. Using plastic pipes makes the metal connection between stand pipes and metal towel warmers break. So the potential breaks: stand and mixer (or towel warmer) have different potentials. This phenomenon is called potential difference. Electric current starts between two different potentials – the only condition is that there is a conductor between them. Flowing water is exactly that. When water is moving in the pipes, a minimal friction occurs between different mediums (water and metal), and this friction creates voltage. I.e. the potential in the stand is equal to ground’s potential (it means it’s grounded), and the one in the towel warmer is completely separate from others. Water acts as a medium between two different potentials, therefore creating alternating electric currents. The result is corrosion.
Water is an excellent electric conductor. ALL that you NEED TO DO is to ensure a reliable metal connection between stand pipes and bathroom equipment (mixer, towel warmer). To put in bluntly – ground your towel warmer through metal stand pipes, and all variable troubles will be left behind. The potential will recover, and the current will have nowhere to move.
When using plastic and metal pipes, ALL metal system elements (heating radiators, towel warmers, sinks, bathtubs, mixers and even cast-iron toilet cisterns) must be grounded. Everyone can decide on their own: whether to continue laboratory studies for the topic “Grounding as a method to cope with electric corrosion” or simply buy an electric towel warmer.