Water and electrical components: sworn enemies?

Water and electrical components: sworn enemies?

25 October 2019 Off By Facto Edizioni

/ by Aldo Avancini /

A physics lesson with practical implications.

Ing. Aldo Avancini / Proposta Srl

I like the concept of “the devil and the holy water”, also the name of an Italian restaurant well known for its excellent cuisine and warm welcome (but I won’t tell you where it is). I especially like it because it can highlight concepts that at a first glance do not seem comparable, yet actually this is due to poor, incorrect and often bad or distorted information. A typical example involves water and electricity, entities that are often considered incompatible. I would therefore like to propose some considerations on this issue, focusing on a more technical approach. 

Electric charges (electrons) flow between 2 elements with different potential yet connected via conductive material (together called a ‘circuit’) with the aim of restoring balance between the 2 elements, stopping when this is reached or when the circuit is interrupted. Therefore, when there is a difference in potential, electrically charged entities (electrons) will be subjected to a force that will cause them to move, in accordance with the laws of physics; the ordered movement of these electrically-charged elements is referred to as “electric current” and its “intensity” can be measured. To clarify however: as these elements (electrons in metallic materials) are negatively charged, they will be released by something that is negatively charged and will migrate towards something else that is positively charged, the exact opposite of what is commonly believed.

This clarification actually has little influence on common beliefs, indeed the commonly-accepted convention is +>- (from higher to lower energy level). Far more important, on the other hand, is the concept of the number of these negatively charged elements that are free to move, and therefore water is considered as being something that must absolutely be kept separate from electrical components. 

To carry energy, water needs these “electrically charged elements” (electrons, although in this case it is more appropriate to call them ions); therefore the more ions there are in the water (or liquid in general), the more electricity (energy) will be transferred! Does anyone remember the old swing chain rides where the operator adjusted the speed by varying the immersion of a copper plate in a container containing a saline solution? And that the depth of immersion of the plate and the amount of salt dissolved in the water were elements that controlled the speed of the ride? However, this highlights a second important consideration, namely that if the amount of ions defines the current carried, ions must be present! Contrary to belief, the conductivity of water does not reach very high values, precisely because this depends on the quantity of ions suspended in the liquid, ions that are responsible for carrying electricity; indeed the conductivity of drinking water is 100 to 1,000 times lower than the conductivity of sea water (the range varies so greatly because the characteristics of drinking and sea water are not uniquely defined). And it is even lower in the case of distilled water.

What does all of this mean? It means that electrical equipment can be used underwater, provided that precautions are adopted to prevent negative events occurring to both the systems and the health of people/users. The concept (applied quite often) of “I placed the pump away from the tank” does not solve the problem, on the contrary it brings losses in load that may be significant, with a consequent increase in the power required. The costs of both the system and the energy needed to move the water thus increase, due to dynamic restrictions, i.e. fittings, junctions/T connectors, measuring devices, sections of smaller diameter pipes, perhaps at high speed, etc., perhaps underestimating how much energy lost from rough walls or wet sections, changes in cross-section and so on.

I can conclude by saying that today the most common electrical devices (pumps, motors, etc.) are available with continuous immersion configurations. They can work with complete safety and reliability, as long as they are positioned and above all powered correctly (wiring protected electrically and mechanically).

Taken from Games&Parks Industry October 2019, page 100

Ing. Aldo Avancini /  Proposta Srl / proposta_design@yahoo.it