backfeeding

Backfeeding is the flow of electrical power in the reverse direction through a system, typically from an alternate power source such as a generator, solar photovoltaic system, or uninterruptible power supply back into a building’s wiring or into the utility distribution network. In normal operation, power flows from the utility to loads; backfeeding describes energy traveling from the source toward the grid or through unintended paths within the installation.

Causes include connecting a generator or inverter directly to a building’s electrical panel without a proper transfer switch or interlock, or miswiring that creates a cross-connection. Grid-tied solar or wind systems can backfeed the utility lines if protection mechanisms fail or are not properly implemented. Backfeeding can occur during outages if a system remains energized when utility power is restored.

Risks associated with backfeeding include energizing exposed conductors, posing shock hazards to utility workers and others, potential damage to electrical equipment, and increased fire risk. It can also bypass or defeat protective devices, making it harder to isolate faults and increasing the chance of arc faults or equipment failure.

Prevention and safety measures focus on isolation and proper interconnection. Use listed transfer switches or interlock kits to physically separate alternate power sources from the grid. Install backfeed protection devices and ensure grid-tied inverters have anti-islanding capability. Adhere to local electrical codes, obtain professional installation, and employ lockout/tagout procedures when servicing systems.

In some contexts, deliberate backfeeding is part of microgrid or emergency power designs, where it is essential to maintain isolation from the grid during outages. Proper design and compliance with standards are crucial in such setups.