What Is Backfeed?
Backfeed is the unintended flow of electrical power from a generator, solar system, battery, or another source into wiring that utility power normally supplies. The condition can energize circuits believed to be de-energized and create dangerous voltage at equipment or utility lines. A properly installed transfer switch prevents this unwanted connection.
Quick Facts About Backfeed
Category
Electrical power-flow condition
Used for
Generator and alternate-power system checks
Common confusion
Mistaken for normal generator operation
Also called
Reverse feeding, Generator backfeed
Often discussed with
Generator Installation
Key Takeaways About Backfeed
- Backfeed creates an unwanted connection between separate power sources.
- A transfer switch controls which source supplies the building.
- Backfeed is not the same as normal generator operation.
How Backfeed Works
Backfeed occurs when an alternate power source connects to building wiring without the source-selection control working as intended. During a generator installation, a transfer switch separates utility power from generator power before the generator supplies selected circuits. The switch changes the electrical path so both sources do not feed the same conductors.
Related glossary terms: Transfer Switch, Manual Transfer Switch, Standby Generator.
Improper connections can send generator power through a branch circuit, panelboard, service entrance, or utility connection. The result depends on the wiring arrangement and the condition of the switching equipment. Electricians check source conductors, neutral connections, grounding paths, and interlocking parts to confirm that the intended source reaches the intended loads. A generator inlet and transfer equipment must match the system design.
From the GMB Electric team
When we handle a generator installation, we trace each source path and verify how the transfer equipment isolates utility power. We also check conductor terminations, neutral behavior, grounding connections, and panel labeling. Our team treats unexpected voltage on an isolated circuit as a condition that requires investigation before the system operates.
Backfeed in Practice: A Real-World Example
A homeowner connects a portable generator to a building through an improvised cord, allowing generator power to travel through branch-circuit wiring. A correctly installed transfer switch directs generator power to selected loads and keeps the utility connection separate.
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