Backfeeding

Lore & Background

Backfeeding occurs when electric power flows in the reverse direction of typical flow. Intentional backfeeding has increased with consumer power generation equipment such as wind turbines and photovoltaic systems, where excess power may be fed back into the electrical grid if supported by the utility provider. In such cases, a specially engineered electrical meter capable of net metering is installed. Unintentional backfeeding commonly results from an electrical generator improperly connected to a building electrical system without a transfer switch or generator interlock kit. Because an electrical transformer can operate in both directions, power from consumer equipment can backfeed through the transformer and energize the distribution line, posing hazards to grid equipment and personnel. Intrinsic backfeeding occurs when a location that is typically a generator becomes a consumer, such as when an electrical generation plant is shut down or operating at reduced capacity and its parasitic load exceeds generated power. Utilities take steps to decrease parasitic load to minimize this type of backfeeding.

Reader's Guide

Backfeeding is significant because it challenges the traditional assumption that power flows in one direction, which underlies most circuit protection and voltage regulation devices used by electric utility companies. Interconnection agreements for intentional backfeeding can involve nontrivial engineering and costly specialized equipment to keep distribution circuits properly protected. Costs may be minimized by limiting distributed generation capacity to less than local consumption and installing a reverse-power cutoff relay. Safety hazards are substantial: personnel working on equipment subject to backfeeding must be aware of all possible power sources and follow systematic protocols. Lineworkers attach temporary protective grounding assemblies that short all conductors to each other and to earth ground to prevent accidental energization. The use of double-ended power cords, which defeat safety mechanisms, is illegal under the United States National Electrical Code due to the hazards of unintentional backfeeding.

Did You Know?

• Backfeeding may be intentional (e.g., net metering with solar panels) or unintentional (e.g., improper generator connection).
• An electrical transformer can operate in both directions, allowing backfeeding to energize distribution lines.
• Intrinsic backfeeding occurs when a power plant's parasitic load exceeds its generated power during shutdown or reduced operation.
• Double-ended power cords are illegal under the United States National Electrical Code due to backfeeding hazards.