This paper details the design, construction, and test of a lightweight, low energy usage Thomson Coil actuator for the operation of a commercial medium-voltage vacuum switch. A novel latching design, directly linked to the actuator armature, helps to keep the actuator mass at minimum. Experimental results show that 125 J of electric energy is sufficient for operation of a commercial 27 kV vacuum interrupter in times suitable for medium-voltage dc protection applications. The use of high conductor density coils is shown to play a key role on the observed actuator performance. Finite element simulations are used to demonstrate that shorter operation times are feasible, without augmenting the consumed electrical energy, by further increasing coil conductor density.