Reversed direction of the arrester installation. You shall connect the external network cable to the “IN” end and 
connect the switch Ethernet port to the “OUT” end. 
  Poor arrester grounding. The length of the grounding line should be as short as possible to ensure that it is in good 
contact with the switch grounding terminal. Use the multimeter to confirm the contact condition after the grounding.   
  Incomplete arrester installation. If there is more than one port connected to the peer device on the switch, it needs to 
install the arresters on all connection ports for the purpose of the lightning protection.