Safety issues and damage to equipment with both Smart Grid and home network connections

Equipment getting power from the Smart Grid often has connections to the home network, a configuration which during a lightning storm is prone to safety issues and damage. Lightning can occur as direct strikes to a service, or as nearby strikes which induce currents in a service. Protection against these events is important, and existing standards deal with these. But there is a situation that existing standards have not considered, and it can result in a shock hazard and equipment failure. This potential failure is caused by Ground Potential Rise (GPR), in a site which has two or more ground references; for example AC power grounded at the service entrance at one side of a house, and a phone line grounded via a surge protector at the opposite side. The GPR produces a voltage gradient between the two ground references. This high voltage is a potential shock hazard. It can also cause a breach of basic or enhanced insulation, with damage and potential exposure to hazardous voltages resulting. This paper discusses GPRs; how to test an equipment to see if a GPR will cause a problem; and what to do if it does.