I use the normal surface or wall mounted 240v switches. The books say that the surface mounted switches give a faster break of the connection and so result in less sparking and therefore erosion of the switch terminals. They also say that the normal wall mounted type are unsuitable for low voltage and erode quickly. While not being sure of the theory, all I can say is that I have had some wall mounted 240v switches in regular use for over 20 years and have yet to see one fail in service. I have had one fast-break type act up intermittently, however.
