TYPES OF CONNECTIONS BETWEEN ELEMENTS
When two modules connect to, or just come in contact with, each other with the connecting plate surfaces, there are 3 ways this can happen. One way this can happen is if the surfaces only touch each other, but there is no interlocking bond; only pressure or stability are involved, and only pushing but not pulling can take place between the two modules. Another way this can happen is if there is a mechanical interlocking bond; this would be the prefereable means for long term or unpowered bonds. The last is if there is a powered electrical bond; if energy is removed, then the bond is broken; this would be the preferable means of bonding two modules in situations where connections have a very short duration and there is frequent connecting and disconnecting activity. A bond involving both mechanical and powered electrical means is possible and could be considered a fourth way, but in practice this would be extraneous or unnecessary (unless the interlocking mechanism is designed to be breakable by excessive tension and the powered electrical bond is necessary for providing more strengh).
There are 4 types of schematic symbols for depicting 2 modules in contact with each other. In the image below, Figure 2a shows 2 modules A and B connected to each other without reference to the type of bond; Figure 2b shows 2 modules A and B connected without either type of bond; Figure 2c shows 2 modules A and B connected with only a powered electrical bond; finally, Figure 2d shows 2 modules A and B connected with at least a mechanical bond (it either may or may not have a powered electrical bond).