Backfeed is energy flowing into a circuit from a source other than its normal supply: a standby generator connected without a changeover switch, a solar inverter, a second transformer, a parallel feeder or a VT energised from its secondary side. It is one of the main reasons isolations must cover all sources and why equipment is proven dead at the point of work. On distribution networks, backfeeding from a neighbouring feeder is also a deliberate way to restore customers.
Customer plugged a generator into the dryer socket and backfed the transformer, the crew read 7 kV on a line they thought was dead.
Also heard as
- back-feed
- reverse feed
Related terms
Islanding
Condition where part of a network stays energised by local generation after being cut off from the main grid.
Prove dead
To test isolated equipment with a verified voltage detector and confirm no voltage before anyone touches it.
Live
Connected to a source of voltage, or describing a conductor meant to be energised in normal use.
Dead
Isolated from every source, proven free of voltage and safe to work on.