Quote:
Originally Posted by APS
The router power comes via way of a transient protected mains supply and a UPS, so I am pretty sure the surge may have come in via the VM cable.
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First off, how do you know AC electric has any protection from that type of surge? If the UPS does protection, then post a UPS number that says so. Most UPSes have near zero protection. Just enough above zero so that a majority call it 100% protection.
If your AC has transient protection, then that device has a low impedance (ie 'less than 3 meter') connection to single point earth ground. Many transient protectors only claim to suppress noise. A destructive surge easily blows right through those devices.
Second, same applies to an earth ground for that VQ301. To be earthed means a low impedance (ie 'less than 3 meter') connection to earth. So we just pretend those centimeter parts will stop what three kilometers of sky could not.
A wall receptacle safety ground is called earth. An earth ground for protection is a metal plate or rod actually in earth. The two 'earths' are electrically different. Only share a common name. Connecting a VQ301 only to a safety ground means it is not earth, does not connect to a single point ground, and does not do surge protection. To be earthed for surge protection, a connection must be low impedance (ie 'less than 3 meters') to the same earth ground even used by the AC transient protector (that must also make a low impedance connection).
The isolator is doing what should alread exist in appliances - galvanic isolation at 2000 volts. It only provides major transient protection when the screw attaches a wire to a true earth ground.
Without a connection to earth that short, then the isolator can only block small transients. Duplicates (not improve) what should already exist inside each appliance. To make irreleavnt a destructive transient (which you apparently had), an isolator must connect that screw low impedance to a true earth ground.