Jog Circuit Definition
The jog circuit is important to create a circuit that will allow the operator to momentarily energize the circuit without the need of pressing the stop pushbutton. Jog circuits allow the operator to move loads to a set position preventing the load from over traveling to the desired position. The jog circuit can be used in almost any control circuit because it relies on momentary energizing and de-energizing of the pilot device.
Jogging or inching is deﬁned as the quickly repeated closure of a circuit to start a motor from rest for the purpose of accomplishing small movements of rotating machine.
The term jogging is often used when referring to full voltage starting of loads; the term inching can be used to refer to reduced voltage starters. Generally, the terms are used interchangeably because they both prevent a seal-in circuit from being used.
There are many ways to develop a jog control circuit. In designing a jog it is important to remember the overall outcome is to make a load operate during the duration of the start button being activated. This means the control circuit is designed so there is no way for the load to become energized and stay energized through the memory/seal-in contact.
One of the jog circuit designs is the two-circuit pushbutton. The circuit will operate as a normal three wire circuit if the start /stop pushbuttons are used. Pressing the jog button creates a current path directly to the load bypassing the seal-in of the control circuit. However, the potential danger can exist because the jog button can potentially become the active seal-in causing the load to stay on without the assistance of someone pressing the pushbutton. If it is possible to eliminate using pushbuttons that make and break the control circuit at the same time in the same circuit.
Jogging Circuit Operation
Configuration 1. Jog Circuit
The Jog circuit in Configuration 1 operates as follows:
- A switch is wired in series with the seal-in of the pilot device.
- With the switch closed the control circuit acts as a normal stop/start station controlling a load connected to the pilot device, power is sitting on the start and seal-in terminals of the pushbutton.
- Pressing start immediately sends power through the start pushbutton and the seal-in contacting energizing the coil.
- The seal-in contact is now maintaining power to the coil overriding the start pushbutton and it is no longer needed to be held down.
- The coil of the motor starter can be de-energized several ways.
- The motor could go into overload which means the normally closed overload contacts will open breaking the circuit.
- The stop pushbutton can be pressed removing power from the seal-in contact causing the coil to be de-energized.
- The next way the control circuit could be stopped is to turn the switch to the jog position. This will immediately de-energized coil.
- With the switch in the jog position, the pilot device will no longer have power through the seal-in contact.
- The coil can only be energized with the start pushbutton and only for a length of time that the button is pressed.