HP Laserjet 2430dtn NIC issue

You need to have the electrician check out the power socket since one end of the 3 is a ground and if not wired correctly there could be an issue with the network cable somehow interfering or causing a spike over the ethernet cable. Since they say the power socket and cable drop is good, then have them plug in a computer and attach to the network at that location and see if it has an issue.