Hazardous Voltages Caution on National Instrument Switches

Updated Oct 24, 2025

Reported In

Hardware

  • PXIe-2527

Issue Details

 I read in the specifications document for my National Instruments switch:

Caution When hazardous voltages (>42.4 Vpk/60 VDC) are present on any relay terminal, safety low-voltage (≤42.4 Vpk/60 VDC) cannot be connected to any other relay terminal.

What does this mean?  I want to connect voltages over 42.4 Vpk/60 VDC and voltages under 42.4 Vpk/60 VDC to my switch at the same time.  Is this OK?

Solution


Yes, it is OK to connect voltages that are above and below 42.4 Vpk/60 VDC to the same switch (if the switch is rated for those voltages).  UL defines 42.4 Vpk/60 VDC as the breakdown voltage of human skin; voltages below these limits are generally considered safe to touch, while voltages above these limits can cause injury or death. 

When any high voltage is present on a switch module, it is important  to consider every line as if it were a hazardous voltage for safety purposes.  If even one line connecting to the switch could contain signals over 42.4 Vpk/60 VDC, you must treat all other lines on that module as if they are hazardous voltages.  This is a safety consideration to prevent injury or death if user error or relay failure results in a low voltage line connecting to a hazardous voltage line.

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