power consumption of a switch
Switching losses are both mechanical and electrical and depend on many factors:
- dielectric strengh of insulating media
- mechanical opening/closing speed of contacts
- AC or DC switching
- loads: inductive, capacitive or resistive
- Voltage/current amplitude
Switching is a transient phenomena and losses are mostly a concern for opening as some arcing always occurs between the 2 contacts. This arcing creates pitting (small crevices on the contact surface) and may even destroy them. Switching AC is much easier than DC since a zero crossing occurs every half cycle and thus extinguishes the arc. If the contact moving speed is quick enough, the current might sometime be interrupted at the first zero crossing but to obtain this behaviour strong opening springs are needed. Otherwise, slow moving contacts will increase switching losses to such a level that melting will occur. In a HV breaker, which sometime needs to open on a short-circuit (up to 50kA on transmission lines) several "automotive sized" springs provide the mechanical energy needed to operate the main contacts, which, incidently are made of tungsten to «survive» arcing. Dielectric strenght is also an important factor: dry air can whitstand about 3kV/mm but arcing ionizes air and thus contacts gap must be quite large to compensate (HV breakers have SF6 insulated main contacts). 
On a much smaller scale, common switches have a spring operated mechanism which provides a toggling effect, speeding up contact displacement, and preventing them from staying «in between» (where arcing occurs). 
Opening a DC current is much more difficult since there is obviously no zero crossing and more resilient contact metal is needed, magnets are even used to lenghten arcing path. Closing a switch (or relay) is generally easier on contacts since arcing will only start at the very end of closing, but, unfortunatly, most contact have some bouncing which increases arcing time... Last, but not least, opening an inductive load is usually the  limiting factor on any switch, relay or contactor since an inductor tries do resists to any current variation and will thus «react» by generating a very high voltage (precisely what is used to generate sparks in ICE motors...) which will increase arcing and switching losses...