That's mechanical tension, not high voltage.
Leviton’s new RTT99 Receptacle Tension Tester is a versatile digital handheld device that measures the amount of
retention force applied to inserted plug blades by line and ground contacts in electrical receptacles and outlets.
Individual line and ground contact forces are measured quickly and accurately and displayed digitally, allowing the user
to record the retention force of each contact. The RTT99 is intended for use in 15 or 20 Amp straight blade receptacles
and outlets rated at 125 or 250 Volt
http://communities.leviton.com/servlet/JiveServlet/previewBody/2143-102-1-3291/Spec RTT99.pdf
Leviton’s new RTT99 Receptacle Tension Tester is a versatile digital handheld device that measures the amount of
retention force applied to inserted plug blades by line and ground contacts in electrical receptacles and outlets.
Individual line and ground contact forces are measured quickly and accurately and displayed digitally, allowing the user
to record the retention force of each contact. The RTT99 is intended for use in 15 or 20 Amp straight blade receptacles
and outlets rated at 125 or 250 Volt
http://communities.leviton.com/servlet/JiveServlet/previewBody/2143-102-1-3291/Spec RTT99.pdf
. I guess that is all you need for something like this. A spring and a dial.
