Circuit Reclosers Probed as Potential Cause of California Fires

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Automatic circuit recloser generating sparks at a simulated line fault. Photo: S&C Electric

Wind-swept fires that killed more than 40 people in California in recent months have also jolted the state’s biggest utilities, Pacific Gas & Electric (PG&E) and Southern California Edison (SCE). The utilities have had to work around the clock to keep power flowing to fire-afflicted communities, even as their equipment and policies face scrutiny as potential contributors to the deadly fires. California regulatorspoliticians and trial lawyers are querying SCE and PG&E’s tree trimming and line maintenance — common culprits in prior California fires — but they are also examining a utility device that produces sparks by design: automatic circuit reclosers.

Automatic reclosers are pole-mounted circuit breakers that can quickly restore power after outages, but they can also multiply the fire risk from damaged lines. While SCE is adjusting recloser operations to reduce fire risks, PG&E’s practices are less clear. And only their neighbor to the south — San Diego Gas & Electric (SDG&E) — is tapping advanced recloser technology that is safer by design.

Reclosers make quick work of many line faults, the great majority of which result from temporary insults such as a branch striking a line or the electrocution of an unlucky squirrel. As Australian recloser manufacturer NOJA Power puts it: “Like the success of Vanilla Ice, Dexy’s Midnight Runners and Devo, most network faults are transient.” In such cases the recloser detects a power surge, momentarily interrupts electricity flow, and then automatically re-closes its contacts to restart flow down the affected line.

Reclosers usually try restarting a line 2-3 times before giving up and “locking out” a line. Sometimes multiple attempts are needed to do the job, writes NOJA Power, such as when high-temperature electrical arcing at the site of the fault burns away hung trees or tree limbs.

Under the wrong conditions, however, such arcing and ignition can obviously spark a fire. Reclosers contributed to several of Australia’s deadly Black Saturday bushfires of February 7, 2009, according to the official report of the Victorian Bushfires Royal Commission. Continue reading

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