RS485 / RS422 communications uses signals that are at most +/- 12VDC, and typically, +/- 5VDC
So usually, it is perfectly safe to hold the Resistor/LED combination on the comms wires without any chance of an electric shock.
Since you have got comms problems, there is obviously something wrong with the system, and one possible cause of a problem is that mains voltage is present on the comms wires, and this has blown up the converter - this mains voltage may still be present on the wires!
If you are in any way unsure, use a voltmeter to check the voltage across the terminals and from the terminals to ground first.
Be careful, always check the wiring carefully first and with a voltmeter to ensure that everything is safe before you touch the comms wiring.
If you are testing around the back of the instrument, make sure you know where the mains supply terminals are - if in doubt, isolate the supply first, although check if this also isolates the comms wiring or converter power supply.
Don’t blame us if you get a shock - check it first!
(C) 2014 SpecView Corp & SpecView Ltd. Page Updated: 15 January 2021
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