Pushbutton & E-Stops: What’s the Difference?

If you have ever found yourself looking for the right emergency stop switch to add to your machine build or industrial equipment you have most likely come across a wide variety of terms that refer to this important piece of equipment. From e-stop to emergency push button, or kill switch just to name a few, there is a laundry list of ways people identify this small but integral instrument.

Now all emergency stop buttons are pushbuttons by nature, but not all pushbuttons are emergency stop buttons. So, what sets an emergency stop button apart from its counterpart that is usually found right next to each other on the same piece of equipment?

To answer this question, we must first understand the parts that make up an emergency pushbutton switch. An emergency switch, and pushbuttons in general, are composed of three main parts; the actuator, which is the fancy term for the button you push, the contact blocks, and the actuator holder which connects the push button to the contact blocks. 

Pushbutton Switch Parts:

  • The Actuator
  • The Contact Blocks
  • The Actuator Holder

It is in the contact blocks, sometimes referred to as elements, that we find the main difference between e-stops and regular ole pushbuttons. Specifically, the different states in which the contact blocks sit, either normally open (NO) or normally closed (NC).

A normally open contact (NO) is usually found on standard pushbuttons that are used to start a machine or procedure by acting as a bridge to connect a power source on one side of the contact block to the machinery that needs the power on the other side of the element. The pushbutton acts as a switch that completes a circuit that allows power to flow to a machine to allow it to do its job. Think of when you flip a switch in your house and the light turns on. The switch acts as a level that completes the circuit when turned to the on-position that allows electricity to freely flow to the light bulb so it can do its job and provide you with light!

Now an emergency stop button on the other hand sits in the exact opposite state of a general pushbutton. It is always normally closed, meaning that the circuit is already connected so that power can flow freely from the source to the piece of equipment, or load, that needs it. It is only when you push the emergency stop button that it breaks the loop and cuts off the electrical current from reaching the equipment.

Why would you want something that cuts the power to a piece of equipment and stops it from doing its job you may ask? Well, it’s because the function of an emergency stop button is to act as a safety mechanism in the case of an emergency to quickly cut power to a piece of equipment making it stop all functions immediately when it cannot be shut down manually by a user, therefore, preventing the risk of injury or hazard on the factory floor. This is why you will almost always see a piece of equipment that has both a pushbutton, used to turn on the machine and usually identified by a green round or square pushbutton, and an emergency stop switch, which is indicated on by a big, red, round, mushroom button.

Now, unlike a pushbutton, whose design is not usually regulated, an emergency stop button’s appearance is highly regulated by strict standards depending on the region you are operating in, like NEMA in North America, and EN in Europe that demand specific designs considerations to make sure the emergency button can easily be identified and operated in an emergency situation.

Some other e-stop design requirements include.

  1. Have a direct opening mechanism installed on the (NC) contact
  2. Feature a self-holding function
  3. Have a button that is a “mushroom” head design or something equally easy to use
  4. A red color button on top of a yellow background.

Further, resetting the emergency stop switch should only be possible by way of a direct manual action taken by the operator at the spot where the emergency stop was initiated. How this is done is determined by the type of emergency stop you decide to use. Some work by turning a key to get the e-stop back in its original NC position, in some instances you must rotate the button back to its initial starting point, or by forcefully pulling the e-stop back into a normally closed state (NC)

Now that you have a better understanding of what sets an Emergency stop button apart from a pushbutton switch, check out MISUMI’s new offering of IDEC pushbutton and emergency stop switch products.

About the Author

Michael Cox

Michael is an Associate Product Manager with a degree in Engineering from the University of Missouri. He started his professional career in chemical sales before coming to MISUMI 5 years ago. Since that time Michael has built and managed many key electrical brands that include MurrElektronik, Mitsubishi, IDEC, and Binder.

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