How X Safety Capacitor and Y Safety Capacitor Place and Function

In the 220V power supply circuit, you can almost always find safety capacitor. So what kind of capacitor is a safety capacitor? What kind of role does it play?

 

 

Safety capacitors are divided into X capacitor and Y capacitor, if divided according to the dielectric material, safety capacitors are essentially polyester capacitors and ceramic capacitors. Polyester capacitor internal
dielectric is polyester, while ceramic capacitor internal dielectric is ceramic. The reason why it is called a safety capacitor, because it passed the safety specification test certification, in line with national safety standards, and when the capacitor fails will not catch fire, will not threaten the safety of life.

 

Safety capacitors are used at the very beginning of the 220V alternating current, the X capacitor is located between the neutral wire and the live wire, and there are two Y capacitors, one is located between the live wire and the ground, and the other one is located between the neutral wire and the ground. The main function of the safety capacitor is to filter the interference signal. Note that the capacitor filters out not 220V AC, but abnormal high-frequency pulses. These signals can be caused by lightning, plugging and unplugging of sockets, etc. Although they both filter out interfering signals, the X and Y capacitors filter out different types of interference: the X capacitor filters out differential mode interference, while the Y capacitor filters out common mode interference.

 

 

Let's start with the X-capacitor. For example, if a high-frequency interfering signal suddenly comes from the live wire, it will be filtered out by the X-capacitor. The direction of flow of the interference signal is like this: if it comes in from the live wire, then it will flow away from the neutral wire After the X capacitor before and after the signal amplitude is almost unchanged, but the phase is 180 ° difference, so it is said to be a differential mode interference, differential mode is the phase difference. Plus Y capacitance, if the two lines at the same time by the same signal interference, then at this time their amplitude and phase should be the same, so it is called common-mode interference, at this time the X capacitor will not play a role, because the capacitor voltage on both sides of the same time to increase, then the capacitor will not have a way to charge. We know that the capacitor can be charged because there is a potential difference, so the capacitor can store charge, and at this time the capacitor voltage on both sides of the same, so there is no way to charge, at this time the X capacitor will not play a role.

 

 

 

Let's take a look at the Y capacitor. Its other end is directly connected to the earth, the earth can be regarded as zero potential, so at this time the two Y capacitors can play a role. Incoming high-frequency interference signals will flow through the Y capacitor to ground, which is why the X capacitor filters out differential mode interference, while the Y capacitor filters out common mode interference.

 

There is another problem, we know that the main role of the electrolytic capacitor is filtering, will it be better with electrolytic capacitors ?

This is absolutely not. Because the electrolytic capacitor only allows the addition of positive voltage, and 220V AC negative half cycle is the reverse voltage, to the electrolytic capacitor with 220V AC, will make it explode and catch fire.

We know that X capacitor is actually polyester capacitor, and Y capacitor is ceramic capacitor, these capacitors are not positive and negative poles.

 

So regular polyester, ceramic capacitors can replace the safety capacitors? This is also not possible.

For example, a standard voltage AC250V X (X2) capacitor, its true withstand voltage up to 2500V, while the standard voltage AC250V Y (Y2) capacitor, its true withstand voltage up to 5000V. So the regular standard voltage AC250V ordinary capacitors are not used to replace the safety capacitors.

 

UF Capacitor, as a leading player in electronic components, we supply both X safety capacitor and Y safety capacitor. Here below is our cross reference.

If you are looking for more components, welcome send inquiry: carey@ufcapacitors.com

Or visit our website: www.ufcapacitors.com

 

UF  Capacitors Safety Capacitor Cross Reference
Photo	Description	UF Capacitors' Series Code	Vishay	TDK/Epcos	Murata	AVX/Mallory
	X1Y1 Safety Ceramic Capacitor 500VAC	Y1 Series	30LVS Series VY1 Series	CD45 Series	DE1 Series	K1Y Series
	X1Y2 Safety Ceramic Capacitor 250VAC，300VAC	Y2 Series	WYO Series 25Y Series VY2 Series VKO Series	CS45 Series	DE2 Series	KJY Series K2Y Series
Photo	Description	UF Capacitors' Series Code	Vishay SPRAGUE	Kemet	Panasonic	TDK/EPCOS
	X2 Metallized Polypropylene Film Capacitor	X2 Series	MKP3382 Series MKP3384 Series MKP3392 Series	R46 Series PHE840M Series PHE850 Series PMR-209 Series	ECQU Series	B32921C/D-B32928C/D Series B81 130 Series
Photo	Description	UF Capacitors' Series Code	Vishay SPRAGUE	Panasonic	Faratronic	TDK/EPCOS
	Box-Type Metallized Polypropylene FilmInterference Suppression Capacitor (MPY/Y2)	Y2 Series	BFC2338	ECQUBAF	C43Q1	B3202