Keithley 3933A Operator's Manual page 5

Safety Precautions
The following safety precautions should be observed before using the Model 3933A Phase Shifter and any associated
instruments.
This instrument is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety
precautions required to avoid possible injury. Read over this manual carefully before using the instrument.
Exercise extreme caution when a shock hazard is present at the test circuit. The American National Standards Institute
(ANSI) states that a shock hazard exists when voltage levels greater than 30V rms or 42.4V peak are present. A good
safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring.
Inspect the connecting cables and test leads for possible wear, cracks, or breaks before each use.
For maximum safety, do not touch the test cables or any instruments while power is applied to the circuit under test.
Turn off the power and discharge any capacitors before connecting or disconnecting cables from the instrument.
Do not touch any object which could provide a current path to the common side of the circuit under test or power line
(earth) ground. Always make measurements with dry hands while standing on a dry, insulated surface capable of with-
standing the voltage being measured.
Do not apply more than 42V peak between the outer shell of any BNC connector and chassis ground.
Instrumentation and accessories should not be connected to humans.