PlantFlow 3D › Guides › Emergency stop circuits: how an E-stop should be wired
Emergency stop circuits: how an E-stop should be wired
How emergency stop buttons work, why they use normally closed latching contacts, where to wire them, and why releasing an E-stop must not restart a machine.
What makes an emergency stop different
An emergency stop is a red mushroom-head button on a yellow background, placed where the operator can reach it quickly. When pressed it latches: its normally closed contact (often 11-12) stays open until the button is twisted or pulled to release it.
Normally closed contacts are used because a broken wire or a loose terminal then stops the machine instead of hiding the fault.
Where it goes in the circuit
In a simple starter the E-stop contact is wired in series with the STOP button, before the START and seal-in branch, so pressing it removes the supply from the contactor coil. In larger machines the E-stop feeds a safety relay that monitors two channels and its own contacts.
Because the seal-in contact drops out when the coil loses power, releasing the E-stop does not restart the motor. The operator must reset and press START again. Any design that restarts by itself after release is wrong.
Testing an E-stop
Test each E-stop with the machine running: the motor must stop, it must stay stopped after the button is released, and START must work only after release. Record the test. Also check that the yellow background and the reach distance are correct.
Safety functions of real machines are designed and validated to the applicable machinery safety standards by competent people; this guide explains the principle only.
Try it yourself
In the simulator add an Emergency stop with ＋ Part, wire it in series with S0, then press it while the motor runs. Release it and confirm the motor stays stopped.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.