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Safety Capacitors - What are they?

Safety Capacitors - What are they?
Safety capacitors are more commonly used than you think and not only by power electronics engineers. For example, everything with an EMI-filter on board has safety capacitors incorporated into that circuit. There are still many engineers out there that know little about these important parts because they do not actually use them themselves so in this article we will explain what there is to know about these capacitors.
If you already know about safety capacitors, you can find more information on our portfolio of Knowles Precision Devices Safety-Certified MLCC here.
What is the function of a safety capacitor?
The name already indicates that these capacitors provide safety of some sort. Think of the fact that all equipment connected to the power line needs to be protected from unwanted signals/surges whilst it by regulation it should also prevent causing noise to others. This means that they serve a multitude of purposes. We have listed the main ones below;
  • Filter EMI on the AC Line 
  • Handle surges and high voltage transcients
  • Return path to common / differential mode currents
  • Protect the user of the device
We do not use the same type of safety capacitor for each application, that is why we will continue by looking at what types of safety capacitor there are.
Types of safety capacitors
We generally distinguish two types of safety capacitors, referred to as X Capacitors and Y Capacitors. These are available in different gradations defined by UL60384-14 and EN60384-14 specifications. It is important to know the differences.
Class X Safety Capacitors are usually placed between the wires where the AC current comes in. For most applications a failure of this capacitor would lead a deficiency in the circuit with the result that it might not function as it should. These capacitors are also called 'accross the line capacitors'.
Class Y Safety Capacitors are also known as 'life to ground capacitors' because they bypass the line. If this device does not do its work, the user of the device could get an electric shock so there is a reason that these safety capacitors are generally tied to stricter regulation.
In the UL60384-14 and EN60384-14 specifications it is defined what criteria each type of capacitor should meet. Note that there are different measures for certain X Capacitors and Y Capacitors.
It is possible to place Y Capacitors where initially X Capacitors would be used, although this makes little sense because the capacitor might be over-specified. Most manufacturers do specify to what level their safety capacitors comply (i.e. Y2 / X1).
The product specialists at Heynen can help you select the right capacitor for your critical application. Even if you do not find a component that entirely fits your requirements, they can guide you towards it because of our short lines to the factory. You can find their contact details below to drop them a line or send an email.

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Our expert(s):

Dennis de la Roy Dennis de la Roy
Please contact Dennis with any questions or business opportunities relating to electronic Components of Heynen. We love to be involved in developing new solutions and bringing these to the Dutch market. Contact form dennis.delaroy@heynen.nl
+31 (0)485 55 09 37

Johan De Ceuster Johan De Ceuster
Please contact Johan with any questions or business opportunities relating to Electronic Components and RF. We love to be involved in developing new solutions and bringing these to the Belgian and Luxembourg market. Contact form johan.de.ceuster@heynen.be
+32 (0)11 60 09 10