Circuit Breaker Field Testing

A breaker that fails to open during a fault is not a maintenance problem — it is a protection failure that lets fault energy destroy the transformer, the bus, and potentially the substation. Breakers fail to interrupt for the same reasons every time: worn contacts, a slow mechanism, or a trip coil that no longer pulls reliably. All three are measurable before the failure, with equipment in the field, on the outage window you already have scheduled.

SSC tests medium- and high-voltage circuit breakers across oil, vacuum, SF6, and air-magnetic designs, from 5 kV to 345 kV. Contact resistance in micro-ohms per IEEE C37.10 detects worn or pitted contacts that will run hot under load and may fail to interrupt. Timing and travel analysis per IEEE C37.09 catches mechanism sluggishness — a breaker that opens 15 milliseconds slower than its nameplate spec was fast enough last year and may not be next year. Primary injection of trip elements verifies that the overcurrent and instantaneous elements actually trip the breaker at their coordination settings, not at some drift value the relay has wandered to. Vacuum interrupter HiPot confirms the bottle still holds adequate vacuum to interrupt fault current. Every test has a name, a standard, and an acceptance criterion in the report.

OEM parts availability and the rebuild option.

The majority of medium-voltage breakers in service on the U.S. distribution and subtransmission grid are ITE, Westinghouse, GE, and Allis-Chalmers designs from the 1960s through 1990s. Most OEMs no longer support those lines. Contact sets, mechanism parts, and trip coils are either discontinued or available only from aftermarket suppliers with variable lead times. Field testing identifies which units have contacts that are still serviceable and which need replacement — and for units that need a rebuild, SSC performs that work in our Palm Harbor shop. The testing crew and the shop crew are the same company, so a unit that fails during a scheduled test round does not require a separate contractor relationship to get repaired.

What to send us before the outage.

For a circuit breaker test scope, we need the breaker manufacturer, model, and voltage class for each unit, the last test date if available, and your outage window. If you have prior test records, send those too — the most useful thing on a maintenance test is the baseline, not the individual reading. We will return a crew-days estimate and a proposal within one business day. Florida and Southeast locations are typically schedulable within two to four weeks for planned work; emergency response is same-day or next-day.