Keithley 2461 Quick Start Manual page 13

When the interlock is asserted, the FORCE and GUARD terminals
should be considered hazardous voltages, even if they are
programmed to a non-hazardous voltage or current.
Potentially hazardous voltages of up to ±250 V may be present at
the Force HI, Sense HI, and Guard terminals when the interlock
circuit is closed. To prevent electrical shock, do not expose
these lines.