Safety of domestic dwellings in stressed electrical grids. A case of backfeed hazard

Between the international challenges, there are incentive policies to reduce energy consumptions, especially in the buildings, and the use of energy from renewable sources. However, the international legislator does not pay the same attention to the safety of domestic dwellings. In many domestic dwellings, it is possible to find a “grounding” system not classified by IEC 60364: the TI-system, that is the system of all domestic dwellings isolated from ground. This paper deals with the backfeed hazard originated by pluggable off-line UPSs, very commons in homes. In particular, when the demand is much more than capacity and when utilities asset management is poor, the utilities adopt frequent power cuts to what they think are low priority load users. The affected users install battery powered automatic switchover type standby off line UPS to supply the loads when utility power is cut. These “affordable” UPS are unsafe. Cases of back feed into utility supply lines from these UPSs and linemen doing maintenance by switching off supply receiving fatal shocks have been noted. This paper examines the reasons for such back feed and gives few methods to eliminate fatal and often unforeseen back feed.