A jogging circuit energizes a motor contactor without engaging the seal-in. The motor runs only while the JOG button is held. Release the button, the coil de-energizes, and the motor stops. No latching, no memory, no sustained run. The operator has direct, momentary control over the shaft.
NEMA ICS defines jogging as the quickly repeated closure of a circuit to start a motor from rest for the purpose of accomplishing small movements of the driven machine. In a standard 3-wire motor control circuit, pressing START energizes the contactor and the seal-in auxiliary contact latches the coil — the motor keeps running after the button is released. Jogging bypasses that latch. The contactor stays energized only through the pushbutton itself, so releasing the button is the stop.
Why Jogging Exists
Jogging is for positioning. A conveyor needs to advance six inches to align a carton under a labeler. A lathe chuck needs a quarter-turn to bring a keyway into reach. A press ram needs to inch down until the die seats against the stock. In each case, the operator needs brief, controlled motor movement — not a full production run.
The alternative is starting the motor in normal run mode and hitting STOP a fraction of a second later. That works on paper. In practice, the delay between pressing START, recognizing the correct position, and pressing STOP is too long for precision work. Inertia carries the shaft past the target. Jogging eliminates the overshoot by keeping the motor under momentary control for the entire movement.
Jogging is also used during installation and commissioning. Bump-testing a motor to verify rotation direction is a jog operation — a half-second pulse is enough to confirm whether the shaft turns clockwise or counter-clockwise without running the machine through a full start cycle.
The Seal-In Problem
In a standard 3-wire circuit, the seal-in auxiliary contact closes the moment the contactor pulls in. That contact creates a parallel path around the START button, holding the coil energized after the button is released. This is the circuit's memory — and it is exactly what jogging needs to defeat.
The challenge is that the seal-in mechanism is inherent to the contactor. The auxiliary contact is mechanically linked to the armature. When the coil energizes, the contact closes. There is no way to electrically tell the auxiliary "close for RUN but stay open for JOG." The auxiliary does not know the difference. It responds to the coil, period.
Implementing jogging safely requires an additional device — something external to the contactor that can selectively enable or disable the seal-in path depending on whether the operator wants sustained run or momentary jog. Two methods are standard in industrial motor control.
Method 1: Selector Switch Jogging
A 2-position maintained selector switch (JOG/RUN) is wired in series with the auxiliary contact in the seal-in path. The switch acts as a gate.
In the RUN position, the selector switch is closed. The seal-in path through the auxiliary contact is complete. Pressing START latches the motor — standard 3-wire behavior.
In the JOG position, the selector switch opens. The seal-in path is broken regardless of whether the auxiliary contact is closed. Pressing START energizes the contactor, but when the button is released, no parallel path exists to hold the coil. The motor stops.
The selector switch method is simple and inexpensive. One maintained switch controls the mode. The circuit requires no additional relay, and the wiring is straightforward — the selector goes in series with the auxiliary contact, and the combined path parallels the START button.
The limitation is physical access. The operator must walk to the selector to change modes. On a machine where the control station is within arm's reach, this is fine. On a long conveyor with remote jog stations, it is not.
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Wire a selector switch jog circuit in the trainer →Method 2: Control Relay Jogging
A control relay (CR) with two electrically isolated NO contact sets replaces the contactor's auxiliary contact as the seal-in device and provides a separate path for the motor coil. A DPDT ice-cube relay is the standard choice. One contact set carries the motor coil current, the other provides seal-in feedback to the relay's own coil. This isolation is what makes safe jogging possible.
The operation splits into two independent paths:
RUN path: Pressing RUN energizes the CR coil. One CR contact set (NO) closes and passes power to the motor contactor coil. The other CR contact set (NO) closes and feeds power back to the CR coil — the CR seals itself in. The contactor stays energized after the RUN button is released, just like a standard 3-wire circuit.
JOG path: Pressing JOG energizes the motor contactor coil directly, bypassing the CR entirely. The CR coil never sees current. Its contacts never close. No seal-in path forms. When JOG is released, the contactor coil has no holding path and de-energizes immediately.
Contact isolation is what keeps these two paths independent. One CR contact set feeds the motor contactor coil. A separate CR contact set seals the CR in. Because these are electrically isolated, the JOG path can energize the contactor directly without any current reaching the CR coil through either contact set. The RUN path latches the motor through one set of contacts while maintaining the CR through the other. The JOG path bypasses both entirely.
The control relay method is more complex than the selector switch, but it solves the access problem. The JOG button itself controls the mode. An operator at a remote station can jog without walking to a selector switch. The mode is determined by which button is pressed, not by the position of a switch somewhere else on the machine.
Reading is one thing — wiring it yourself is another. Open the interactive trainer and build this circuit from scratch.
Wire a control relay jog circuit in the trainer →When to Use Each Method
The choice between selector switch and control relay is driven by the application, not by one method being superior to the other.
Selector switch jogging fits machines where the operator works at a fixed station and mode changes are infrequent. The circuit is simpler, uses fewer components, and is easier to troubleshoot. A single-station conveyor drive with occasional jog needs during setup is a typical application.
Control relay jogging fits machines where operators need to jog from remote locations, or where the jog function is used frequently enough that walking to a selector switch is impractical. Multi-station conveyor lines, machine tools with separate jog stations at the point of operation, and equipment where jog and run are used in rapid alternation during production are typical applications.
Both methods preserve low-voltage protection. In either circuit, the buttons are momentary. Power loss de-energizes the coil (or the CR), and the motor will not restart until someone deliberately presses a button. NFPA 79 requires this behavior for most industrial machinery.
The Dangerous Jogging Circuit
There is a third approach that appears in older references and occasionally in the field: a double-acting pushbutton with ganged NO and NC contacts, where the NC contact is wired into the seal-in path. When the button is pressed, the NC contact opens (breaking seal-in) while the NO contact closes (energizing the coil). When the button is released, the NO opens and the NC re-closes.
The problem is a mechanical timing race. Pushbutton contacts are spring-return. The NC contacts may return to their closed position before the contactor armature drops out. If the NC closes while the auxiliary contact is still closed, the seal-in path re-energizes the coil and the motor latches. The button was released, but the motor keeps running.
This failure is intermittent and worsens with wear. It depends on contactor drop-out time, spring return speed, contact bounce characteristics, and mechanical wear on the button mechanism. A new button might release cleanly. After months of use, the spring return accelerates relative to contactor dropout, and the race condition emerges. The circuit works most of the time — which is worse than failing every time, because operators develop confidence in a function that can fail without warning. Motor control references widely regard the double-acting pushbutton method as unsuitable for jogging because of this timing race.
The selector switch and control relay methods eliminate the timing race entirely. The selector switch opens a maintained contact that stays open regardless of contactor state. The control relay isolates the jog path so the seal-in mechanism is never involved during jogging.
Anti-Tieback Protection
NFPA 79 addresses jogging control requirements, including the condition where a JOG button can cause the motor to latch unintentionally. This condition — called "tying back" — occurs when pressing JOG creates a path through the seal-in logic, latching the motor even though the operator expects momentary behavior.
The selector switch method prevents tieback by design. In the JOG position, the maintained selector opens the seal-in path regardless of which buttons are pressed or in what order. The seal-in cannot engage while the selector is in JOG.
The control relay method prevents tieback through path isolation. JOG energizes the motor contactor directly and has no connection to the CR coil. Pressing JOG alone can never energize the CR, so no seal-in path forms and the motor cannot latch through the JOG button. If the operator presses RUN first (intentionally latching the motor via CR seal-in) and then also presses JOG, the CR remains sealed — but that latch came from the deliberate RUN press, not from JOG. The operator uses STOP to de-energize in that case, the same as any normal run condition.
Anti-tieback is worth understanding because improvised jogging circuits — particularly those that route JOG current through a path that can feed back to the seal-in logic — can fail this requirement.
Reading is one thing — wiring it yourself is another. Open the interactive trainer and build this circuit from scratch.
Start with the 3-wire circuit — the foundation for every jogging circuit →Frequently asked questions
What is a jogging circuit?
A jogging circuit energizes a motor contactor without engaging the seal-in contact. The motor runs only while the JOG button is held — releasing the button de-energizes the coil and the motor stops. NEMA ICS defines jogging as the quickly repeated closure of a circuit to start a motor from rest for the purpose of accomplishing small movements of the driven machine. Two standard methods exist: selector switch jogging, which uses a maintained switch to gate the seal-in path, and control relay jogging, which uses a relay with two isolated NO contacts to separate the jog path from the seal-in logic.
What is the difference between jogging and inching?
In common industrial usage, jogging and inching are often used interchangeably. When a distinction is drawn, jogging refers to full-voltage momentary operation and inching refers to reduced-voltage or reduced-speed operation for finer positioning. Not all references maintain this distinction — many motor control textbooks treat them as synonyms. In practice, the meaning depends on the plant, the OEM documentation, and the specific control scheme.
Why not just press START and STOP quickly instead of using a jog circuit?
Timing and overshoot. The delay between pressing START, observing the shaft position, and pressing STOP is long enough for inertia to carry the motor past the target position. Jogging keeps the motor under momentary control for the entire movement — the shaft stops as soon as the button is released. For precision positioning during setup, alignment, or threading, that level of control is the difference between landing on target and having to reverse and try again.
What is the dangerous jogging circuit?
A jogging circuit that uses a double-acting pushbutton with ganged NO and NC contacts. When the button is released, the NC contacts may return to their closed position before the contactor armature drops out — re-energizing the seal-in path and latching the motor. This is a mechanical timing race that fails intermittently and worsens with wear. Motor control references widely regard this method as unsuitable for jogging. The selector switch and control relay methods eliminate the timing race entirely.
What is anti-tieback in a jogging circuit?
Anti-tieback prevents the motor from latching unintentionally through the JOG button. NFPA 79 addresses jogging control requirements including this condition. The selector switch method prevents tieback by opening the seal-in path in the JOG position regardless of button state. The control relay method prevents tieback through path isolation — JOG has no connection to the CR coil, so pressing JOG alone can never create a seal-in latch.
When should I use a selector switch jog circuit vs a control relay jog circuit?
Selector switch jogging is simpler and uses fewer components. It fits machines where the operator works at a fixed station and mode changes are infrequent. Control relay jogging is more complex but allows jogging from remote stations — the JOG button itself controls the mode, so no one has to walk to a selector switch. Choose based on whether operators need to switch between jog and run from different locations.