Emergency stop switch

Thread Starter


Joined Mar 22, 2011
I want an install an emergency switch for my project.I want some guidance on how to wire it successfully with the main on/off switchand loads.I geuss it must be in series with the loads.Or not?

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Joined Feb 5, 2010
it should be in series with the MAIN POWER of your project. You want it to shut off ALL power to the circuits.

By placing it in parallel with your load you would simply short out your power supply(which would work) and might damage the circuit or supply when the overload current flows for the brief period before a fuse opens or a circuit breaker trips.

(Edit: You guys type faster than me, and your answer is shorter) :)


Joined Jun 7, 2009

An emergency stop switch is ment to disconnect the power.
It must also be locking, so no direct switch on is possible.
See this page for more info:

Typically, in industry, an Emergency stop does not remove power from actuators, but rather removes the source of voltage that energizes power relays. As 3 phase is a common power source, it would be inefficient and dangerous to route it through the required 'E' stop locations. 'Control' voltages are what are switched with 'E' stops.

Emergency stops are not required to be lockable. That is the job of a local disconnect, which does switch out the power source.

it should be in series with the MAIN POWER of your project. You want it to shut off ALL power to the circuits.
Often is not desirable to remove power from a PLC/embedded/HMI. Emergency stops will remove the I/0 source voltage, but not disrupt controls, clocks,networks, etc.

The most common implementation of an 'Emergency' stop, is through the use of a master control relay. The source voltage that actuates this relay is interrupted with any number of 'E' stops in series. The 'master control relay', or MCR, will inturn switch out the voltge that drives power relays and field devices.

There is however, nothing wrong with using a simple spst switch to 'turn off' your project from mains power. You should also try and calculate what your expected loading is, and fuse your line. This helps reduce taking out the garbage.
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