## Facts

- Florida Power & Light Co. (FP&L) generated and transmitted electricity using facilities located entirely within Florida.
- FP&L’s system interconnected with Florida Power Corporation (FPCo) at shared transmission nodes (“buses”).
- FPCo interconnected with Georgia Power Company, enabling transfers between Florida and Georgia over the integrated network.
- The Federal Power Commission (FPC) commenced proceedings to determine whether FP&L was engaged in “the transmission of electric energy in interstate commerce” under § 201(b) of the Federal Power Act.
- The FPC relied on expert engineering testimony and power-flow analysis indicating that, when FP&L delivered power into a bus while FPCo simultaneously delivered power from that bus to Georgia, the energy was physically commingled in the network and some portion necessarily flowed into Georgia.
- The FPC found FP&L’s power was transmitted in interstate commerce and asserted jurisdiction; the Fifth Circuit set the order aside for lack of sufficient proof that FP&L’s electricity actually crossed the Florida–Georgia border.

## Issues

1. Whether the FPC could assert jurisdiction under § 201(b) over an intrastate utility based on a finding that its power, once injected into an interconnected grid, was commingled with interstate flows and thus “transmitted in interstate commerce.”
2. Whether the Commission’s commingling-based inference of interstate transmission was supported by substantial evidence such that it had to be upheld on judicial review.

## Decision

- The Supreme Court reversed the Fifth Circuit and remanded.
- The Court held the FPC did not exceed its statutory authority in finding FP&L engaged in the transmission of electric energy in interstate commerce.
- The Court concluded substantial evidence supported the Commission’s technical finding that some portion of FP&L’s power flowed interstate due to commingling in the interconnected system.
- The Court rejected a requirement that the agency prove a specific, traceable quantity of FP&L electricity crossed state lines.
- A dissent would have required a clearer showing of actual interstate transmission by FP&L, warning that commingling theories could overextend federal jurisdiction.

## Legal Principles

- Under the Federal Power Act, a utility may fall within federal jurisdiction for interstate transmission even if its physical facilities are wholly intrastate, where its operations are functionally integrated into an interstate transmission network and power is commingled with interstate flows.
- The Commission need not trace particular electrons or quantify a specific amount of power crossing a border when the interconnected system supports a reasonable inference of interstate transmission.
- Courts reviewing highly technical agency determinations must uphold the agency’s conclusions where the record contains substantial evidence and the agency’s inference has a rational basis, and may not substitute their assessment of technical evidence for the agency’s.

## Conclusion

The Court sustained federal jurisdiction over FP&L because expert-supported findings showed that power injected into an interconnected grid commingled with interstate transfers, making interstate transmission a reasonable inference under the Federal Power Act and requiring judicial deference under the substantial-evidence standard.


Fed. Power Comm'n v. Fla. Power & Light Co., 404 U.S. 453 (1972)