National Instruments NI 9411 Operating Instructions And Specifications page 21

Safety
Safety Voltages
Connect only voltages that are within the following limits.
Channel-to-COM
or V -to-COM ................................ 30 V max,
sup
Isolation
Channel-to-channel .................... None
Channel-to-earth ground
Continuous ........................... 30 V
Withstand ............................. 400 V
Measurement Category I is for measurements performed on
circuits not directly connected to the electrical distribution system
referred to as MAINS voltage. MAINS is a hazardous live electrical
supply system that powers equipment. This category is for
measurements of voltages from specially protected secondary
circuits. Such voltage measurements include signal levels, special
equipment, limited-energy parts of equipment, circuits powered by
regulated low-voltage sources, and electronics.
NI 9411 Operating Instructions and Specifications
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Measurement Category I
, 42.4 V , 60 VDC
rms pk
, verified by a 5 s
rms
dielectric withstand test
20 ni.com