Operation, timing and mechanism
Minimum pickup testing finds the lowest control voltage at which a breaker's trip coil or close coil still operates the mechanism. It shows how much margin the breaker has when battery or control power is weak, and it exposes worn, dirty or sticky actuators before a failure to trip or close.
Minimum pickup voltage testing of trip and close coils measures the lowest direct or alternating control voltage at which the electromagnetic coils of a circuit breaker will operate its mechanism. The trip coil releases the latch that lets the breaker open, and the close coil releases the stored energy that closes it. In the test, the coil is energized from an adjustable supply that starts below the operating range and is raised slowly until the coil acts, and the voltage at that moment is the minimum pickup. The test is applicable to medium-voltage air, oil, vacuum and SF6 breakers, circuit switchers and automatic circuit reclosers, and to low-voltage insulated-case breakers that have electrical operators. Molded-case breakers with shunt trips are covered where the design has a shunt device. In the published acceptance and maintenance specifications the test appears in the sections for these breaker types, with the maintenance version often treated as the more routine item and the acceptance version carrying the reference to the table of control voltage limits that applies.
A breaker's protection is only as dependable as the power that makes it trip. Control power comes from a station battery or, in some installations, a capacitor trip device or a control transformer, and at the moment a fault occurs the supply can sag, particularly after a long period of float charging neglect, with a failing cell, or with a long run of control cable. A trip coil that needs nearly the full nominal voltage to act has little margin and may fail to trip when it is needed, leaving the fault to be cleared by a backup device farther upstream with much greater damage. The close coil matters in the other direction: a breaker that will not close when called upon can leave a load or a bus de-energized or defeat a transfer scheme. Coils and their plungers degrade slowly through dirt, stiff grease, a weak spring, corrosion or a partly shorted winding, and the pickup voltage creeps upward before any in-service failure. The test therefore gives early warning and is a simple, low-cost way to confirm that control power margin exists.
A coil is an electromagnet. When voltage is applied, current builds in the winding according to its resistance and inductance and produces a magnetic force on a plunger or armature. The plunger moves only when that force exceeds the opposing forces, which are the mechanism's latch load, spring force, friction and the weight of the moving parts. At a low enough voltage the current, and so the force, is too small and nothing moves. As the voltage is raised the force increases until it overcomes the load, and the plunger strikes the latch. The voltage at which that first happens is the pickup. Anything that raises the opposing load, such as a dry or gummy latch, a bind in the linkage or a weakened actuator, raises the pickup voltage. Anything that lowers the coil's effective force, such as a shorted turn or a high-resistance connection, does the same. The test is therefore an indirect check of the coil, the plunger and the latch together, and it complements timing and travel tests, which show how fast the whole mechanism moves once it has been released.
The breaker is taken out of service, isolated and grounded under the owner's procedures, and for a drawout breaker it is placed in the test position so that the main contacts are separated from the system. Stored energy in closing springs is respected throughout. For the close coil test, the closing springs are charged, since the coil must have something to release. The normal control supply is disconnected from the coil under test and an adjustable supply with a voltmeter is connected in its place. The supply is set to a low value and then raised in small steps, with a pause between steps, until the coil operates the mechanism, and the voltage at operation is read. The measurement is repeated to confirm that it is consistent. The same method is applied to each trip coil, including secondary trip coils, and to the close coil. The tester takes care to avoid a sudden voltage increase, which can let the coil act at a lower reading than it would under a steady voltage. Coils with a series cutoff switch or an electronic control are handled as the manufacturer directs, and the normal control circuit is restored and verified at the end.
The record holds, for each coil tested, the minimum pickup voltage at which the mechanism operated, together with the identification of the coil as the primary trip, a secondary trip or the close coil. It identifies the breaker and its mechanism, the nominal control voltage of the control circuit, the instrument and adjustable supply used, the type of control power, and the breaker position during the test. The as-found condition, including whether the breaker had been operated recently and whether lubrication was done before testing, is noted along with the operation counter readings. Repeated readings and any variation between them are kept, because a pickup that wanders is itself a sign of a sticky mechanism.
Pickup values are judged against a range that is defined relative to the nominal control voltage, and this page gives no voltage values. The published guidance expects the coil to operate well below the nominal voltage so there is margin when the supply sags, and the table of control voltage limits referenced in ANSI/NETA ATS-2025 and ANSI/NETA MTS-2023 gives the allowed range for each nominal control voltage. Two comparisons support the judgment. One is with the manufacturer's data for the coil and breaker, which governs. The other is with the breaker's own earlier results, because an upward drift over successive tests indicates growing friction or coil deterioration even if each value remains in range. Coils of the same type on similar breakers should give similar results, and an outlier points to a local problem. A pickup that is high, erratic or different between trip and close coils is a reason to inspect the latch, clean and lubricate the mechanism, and test again. For the actual voltage limits, refer to your own licensed copies of the standards named above.
At acceptance the test proves that the coils and latches of a new breaker act with margin and sets the reference for later tests, and the acceptance specification ties the result to the published table of limits. In maintenance the test is repeated on a schedule and after mechanism work, and the emphasis is on drift. The breaker class changes the practice. Medium-voltage drawout breakers are tested in the test position with a test cabinet or jumper. Low-voltage insulated-case breakers with electrical operators have a smaller set of coils and a lower control voltage. Oil, vacuum and SF6 breakers differ in mechanism type, so the energy that must be released differs, but the method of raising the voltage is the same. Reclosers with solenoid or magnetic actuators are tested according to their own control design. Breakers with capacitor trip devices, undervoltage releases or dual trip coils need extra steps so that each device is tested individually, and a breaker with a control supply that is alternating current is tested with an adjustable alternating supply.
The equipment classes and standard sections that call for this test, and the UltraDb forms that carry it.
It is the lowest control voltage at which a trip coil or close coil still moves the mechanism enough to release its latch. It is found by raising a low adjustable voltage until the breaker acts, and it shows how much margin exists when battery or control power is weak.
Friction from dirt or dry grease, a weakened actuator or a degrading coil all raise the voltage needed to operate the mechanism. A steady rise over several tests warns that the breaker may eventually fail to trip or close, even though it still works at full control voltage.
No. Pickup finds the lowest voltage that releases the latch, while timing measures how quickly the mechanism and contacts move once released. The two tests complement each other: one checks the margin of the control power, the other checks the speed of the mechanism.
They are published as a table of limits tied to nominal control voltage in the maintenance and acceptance specifications, ANSI/NETA MTS-2023 and ANSI/NETA ATS-2025, and in the manufacturer's data. Use your licensed copies and the breaker's own history for comparison.
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