How a high Earth to Neutral voltage affects electronic equipment like L2 or L3 switches?
5V earth to neutral voltage is perfectly normal under certain conditions (for example a long run of single ended single phase wiring) and should not be a problem for any competently designed equipment. Heck many countries have reversible plugs, so there is a 50% chance that the &quot;neutral&quot; connection of the equipment will actually end up being connected to the live conductor. Equipment standards take this into account.
Generally in electronic equipment the mains goes almost immediately into a bridge rectifier that does not treat live any different from neutral.
Whatever is killing your communications equipment I can confidently state that 5 volts or so between earth and neutral is not it.
What would be a much bigger problem is if you have a three phase (or split phase) system with a high-impedance neutral. If the load is well-balanced it could well be that the earth to neutral voltage is normally fairly low, but that switching transients lead to brief excursions to much higher voltages. 400V into a peice of 230V equipment, even briefly, could very well do damage.
It may be that the field techs have picked up on the neutral to earth voltage, not because it's a problem in itself, but because (in a 3 phase with neutral or split phase system) it is a symptom of a high-impedance neutral.