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General technical information of (RFI/EMI)Noise suppression capacitors on AC mains
【Table of contents】
=================================================================================================
Introduction

1 The need for (RFI/EMI)noise suppression
2 Noise transmission
⑴Radiated noise
⑵Conductive noise
3 Principle of noise suppression
4 What is a noise suppression capacitor?
5 Normal mode noise and Common mode noise
⑴Normal(Differential)mode noise
⑵Common mode noise
6 Operating principle of noise suppression capacitors
Noise Suppression capacitor agency approval
1 USA(UL)
2 Canada(CSA)
3 IEC
4 European Community(ENEC:Eurpoe Norms Electrical Certification)
Noise Suppression capacitor class ratings
1 Class X capacitors
2 Class Y capacitors
3 Sub class
How select the (RFI/EMI)Noise suppression capacitors on AC mains?
Circuit design consideration

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General technical information of (RFI/EMI)Noise suppression capacitors on AC mains
【Introduction】
=================================================================================================
● "CAPAKOR" offers a comprehensive line of (RFI/EMI)noise suppression capacitors on AC mains.
The noise suppression capacitors are used mainly in industrial, consumer and lighting applications for RFI noise suppression and
prevention of electric shock to humans.
①The noise suppression capacitors are used on across the line(line-to-line:class X) and line by-pass(line-to-ground:class Y)AC mains
inputs to electronic or electrical equipment.
②The noise suppression capacitors are subjected to the rigors of the AC mains-not only is the supply voltage always applied,but
also high voltage transient pulses, abnormal surges such as lightning is applied.
Thus, the noise suppression capacitors are designed,
to withstand the above stresses existing on the 50/60Hz AC mains and remain safe without degradation of performance.
to meet the requirements of IEC60384-14 as well as UL-1414 and UL-1283.
③The noise suppression capacitors are manufactured in self-healing metallized film.
〔1〕The need for (RFI/EMI)noise suppression
RFI stands for radio frequency interference and EMI stands for electro magnetic interference.
EMI/RFI is a high frequency/low energy noise,typically of a continuous nature that doesn't directly destroy electronic systems,but
rather disrupts the proper function by overwhelming the normal signal information within the electrical circuitry,thus EMI/RFI means
"decline in the performance of equipment,transmission channels or systems due to noise".
For example,if household vacuum cleaner is running and you are attempting to watch TV.
You may notice lines of interference on the TV screen or even sound distortion.
This interference on the TV is being conducted from the motor of vacuum cleaner through the power lines and into the TV.
Although you may be able to still see and hear the TV,it is not functioning correctly.
This interference may be minor to the TV,but imagine that same interference in medical equipment or an industrial computer
controlling a manufacturing process.
That interference is not just a nuisance and could potentially cause a failure,which might injure a patient or damage a major
manufacturing process.
To prevent such situations,each piece of AC operated equipment must have its noise signal filtered and attenuated to the levels
established by various national agencies.
〔2〕Noise transmission
The RFI noise emanates from almost every kind of electronic equipment all around us,such as,radio,TV receivers,computers,switch
mode power supplies,generators,oscillators,thermostats,neon tubes,household appliances,switching components,thyristors,triacs,
commutators,depending on individual designs or modes of operation.
The noise generated by electronic devices is transmitted through many complicated paths,sometimes through a conductor and
sometimes as radiation,as shown in below fig.1,and the noise can disturb other electronic equipment.

fig. 1
⑴Radiated noise
Frequencies＞30Mhz,the noise tends to radiate directly from the generating circuits.
Radiated noise is transmitted directly into the air from an electronic device,taking the form of an electric wave that interferes with
other electronic devices in adjacent locations ,as shown in fig.1;
③radiated noise transmitted from an electronic device
④radiated noise picked up and generated by the power line which act as an antenna.
⑤radiated noise picked up and generated by the signal lines which act as an antenna.
⑵Conductive noise
Frequencies＜30Mhz,the noise is usually conducted by the AC line and other connections.
Conductive noise interferes with other components and devices by being transmitted along AC mains and the wiring of electronic
circuits,as shown in fig.1;
①conductive noise from electric power line.
②conductive noise along the signal lines connecting electronic devices.
⑦conductive noise entering from the ground line.
And,⑥radiated noise and conductive noise produced from a source within the electronic device.
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〔3〕Principle of noise suppression
The noise suppression is the reduction of the RFI noise.
The principle of noise suppression is to use;
①an AC input filter circuit for conducted noise
②shielding for radiated noise.
〔4〕What is a noise suppression capacitor?
Noise suppression capacitors are identified by various companies as RFI capacitor or radio-interference suppressor or safety
recognized capacitor.
The noise suppression capacitor is a specially designed capacitor used in an AC input filter circuit on the AC mains input to
electronic or electrical equipment,that is between the equipment and the AC mains.
The AC input filter circuit is usually required to meet the conducted noise limits,and the filtering is usually accomplished with the
noise suppression capacitors,often in conjunction with chokes or transformers of various designs.
In the typical application,the noise suppression capacitors are a part of a simple L-C network.
The purpose of the noise suppression capacitors are;
①to stop the(RFI/EMI)noise from entering an electronic system and causing disruption:for protect the equipment from malfunction or
failure,and to stop electrical equipment from putting the(RFI/EMI)noise onto the AC mains:for protect other electrical equipment.
②to protect the electrical system against the voltage surges and the voltage transients.
The voltage surges may be caused by lightning,and,in this case,the energy will be absorbed by the noise suppression capacitor and
not by the electrical circuit.
The voltage transients are voltage spike to which the main voltage is subjected and which can easily occur several times a day in
AC mains with amplitudes of 2000V and above,peak values can be as high as 6KV.
Noise suppression capacitor are used to block and attenuate these voltage spikes.
〔5〕Normal mode noise and Common mode noise
RFI noise is conducted on the AC line either symmetrically or asymmetrically.
And,conductive noise is classified into 2 types according to conduction mode;normal mode noise involving symmetrical noise
components oscillating between lines,and common mode noise involving asymmetrical noise components transmitted a line and
ground,as shown in fig.2-4.
Depending on how they are connected,X and Y capacitors are effective against these different kinds of noise.
⑴Normal(Differential)mode noise
As shown in the fig.2,normal mode noise is conducted on the signal line and electric power line in the opposite direction to each
other.

*noise source:represents the high frequency current generated by switching
transistor in SMPS,for instance.
*signal source:represents either a power source or desired signal source

fig. 2
This type of normal mode noise is suppressed by installing a X capacitor on across the line(=between the line phase),as shown in
the below fig.3.
Thus,noise is returned to the noise source.

fig. 3

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⑵Common mode noise
As shown in the fig.4,common mode noise is conducted on both lines in the same direction,through stray capacitance via ground.

*noise source:represents the high frequency current generated by
switching transistor in SMPS,for instance.
*signal source:represents either a power source or desired signal
source.
*Stray capacitance:are formed whenever 2 conductors are in close
proximity to each other,especially if they are running in parallel.

fig. 4
The circuit is floating from ground (earth potential),and there is a stray capacitance between this circuit and the case.
The common mode noise is directly related to stray capacitance.
The occurrence and effects of stray capacitance- especially at very high frequencies-can lead to greater noise.
To suppress this type of common mode noise,as shown in the fig.5,shock proteced,insulated,earthed,a metalic casing is connected
to the all lines on which noise is conducted by using Y capacitors(=line bypass capacitors).
Thus, bridging the insulation of the equipment.
The noise is returned to the noise source in the following order,signal lines→Y capacitors→metallic casing→stray capacitance→noise
source.

fig. 5
〔6〕Operating principle of noise suppression capacitors
The noise suppression capacitor is the most effective interference component.
Most noise emitted from electronic equipment is at frequencies higher than circuit signals.
The frequency becomes higher,the impedance of the capacitor becomes lower and short circuited.
Thus the noise is forced to go through the capacitors.
The below fig.6 shows an example of noise suppression on an AC power supply line.

fig. 6
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Most noise emitted from electronic equipment is at frequencies higher than circuit signals,and it is forced to go through noise
suppression capacitors which are connected in parallel with the line,are used as side path to return high frequency noise back to the
noise source.
The result is that normal mode noise passes through the X-capacitor and shunted back to the noise source.
The 2 X-capacitors perform the same function with the only difference,1 is for; noise entering the equipment, where the other is for
noise exiting the device.
In the case of common mode noise,the result is that the noise passes through the mid-point of the 2 capacitors to ground.
Depending on the particular design of the electronic or electrical equipment and its other components in the AC line input,various
values of capacitance of the capacitor maybe required to tune the AC input filtering performance.

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General technical information of (RFI/EMI)Noise suppression capacitors on AC mains
【Noise Suppression capacitor agency approval】
=================================================================================================
A capacitor for RFI suppression must be approved by a relevant authority either as a noise suppression capacitor or as part of a
complete unit of equipment.
The various agency requirements for noise suppression capacitors have important differences.
The EC has a different approach to noise suppression capacitors standards compared to UL and CSA.
The EN standard(EC unified or harmonized standards)is quite different in its requirements and rated voltage and it is applied to all
types of AC operated equipment,not just a few selected categories such as UL.
Since most equipment is designed for worldwide use the EN standard is important to North American designers as well as to
Europeans.
〔1〕USA(UL)

At the present time,there are 2 UL standards related to noise suppression capacitors;UL 1283 and UL 1414.
①UL 1283:actually a standard for potted RFI filters.
②UL 1414:noise suppression for application-TV.radio and certain telecom.equipmemt.
UL 1414 is specifically required for TV and radio receivers and certain telecommunications equipment.
rated voltage
UL 1283 ＞250VAC
UL 1414 either 125 or 250VAC
〔2〕Canada(CSA)

Max. capacitance
＞1.0㎌
1.0㎌

Max. operating temperature
＞+85℃
+85℃

CSA requirements closely parallel that of UL,with CSA C22.2No.1 being equivalent to UL1414 and CSA C22.2No.8 being equivalent
to UL1283.
UL and CSA have entered into cross-licensing agreement on a wide variety of standards.
For example,if UL is requested to evaluate an noise suppression capacitor for UL 1414 and CSA C22.2No.1,UL will conduct the
tests common to both standards and those that are different,if any.
Such a capacitor will bear the UL mark and a new "cUL"mark that is fully accepted by CSA.
〔3〕IEC
The IEC is an international body which can pass recommendations but does not in itself have approval power in any country.
IEC 60384-14 is identical to the reference European standard EN132400.
〔4〕European Community(ENEC:Eurpoe Norms Electrical Certification)

With the aim of harmonizing all the European national standards and only one standard of reference,the European Community has
unified the standard of each country.
These unified, or "harmonized"standards are identified with an "EN"designation.
The European standard for noise suppression capacitor is EN132400 which is identical to IEC 60384-14.

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General technical information of (RFI/EMI)Noise suppression capacitors on AC mains
【Noise Suppression capacitor class ratings】
=================================================================================================
The noise suppression capacitors are classified by EN132400 into 2 categories-class X and class Y-these designations are used by
most European countries.
In North America,designations of Across-the-line capacitors,Line bypass capacitors and Antenna couplings refer to following
applications.
＜Class X: Across the line capacitors＞
＜Class Y: Line by-pass capacitors＞
＜Class Y: Antenna couplings＞

fig. 7
fig.8
fig. 9
〔1〕Class X capacitors
①An X capacitor is used in Across-the-line applications,as shown in the fig.3,6 and 7.
②In this location,a failure of the capacitor will not cause anybody to electrical shock hazards and usually will open the fuse and turn
the equipment off.
Therefore;the definition for "X"capacitor application is:"where damage to the capacitor will not lead to the danger of electrical shock".
normal mode RFI noise.
③The X capacitors suppress
④Since,normal mode noise is low-frequency then,X capacitor values are 0.1~1.0㎌.
One would think that a capacitor with a larger constant should be used for suppression against normal-mode noise.
However,increasing the X-capacitor's capacitance causes a problem of increased reactive current.
〔2〕Class Y capacitors
①Class Y capacitor is used in Line-by pass applications,as shown in the fig.5,6 and 8.
②In this location,a failure of the capacitor will cause anybody to electrical shock hazards.
If lightning should strike the AC power line, Y capacitors would be the most likely to be subjected to damage.
If damage occurs, they will not activate any safety fuse.
And,the definition for Y capacitor application is: where damage to the capacitor may involve the danger of electrical shock .
Thus,Y capacitor ratings are very conservative and high electrical and mechanical reliability intended to prevent short circuit in the
capacitor for reasons explained above and considering that in production Y2 are tested at 3,000VDC/μsec vs. 2,000VDC for X2.
Similarly, in the lightning simulation test, the Y2 suppressor must be approved at 5KV vs. 2.5KV for X2.
common mode
RFI noise.
③The Y capacitors suppress
④Since,common mode noise is high-frequency then,Y capacitor values are smaller,0.001~0.0047㎌.
⑤Generally Y capacitors must be kept to smaller capacitance values.
The limitation of the capacitance of Y capacitors is;intended to reduce
❶the energy content of the capacitor to a safe level,when DC voltage is applied.
❷the current flowing through the capacitor when an AC voltage is applied.
Even if,Y capacitors are in a perfect condition, there is some current flowing through them from line to equipment ground.
And,Y capacitor value is indirectly restricted because each application has an allowable max. leakage current(which can range
0.25mA~3.5mA, depending on the AC mains connection).
If larger C values were allowed for Y capacitors,50 or 60Hz leakage current to the ground would be too high for safety standards.
And a too high capacitance of Y capacitor is hazardous if the earth line should be open circuit or disconnected from the earth
grounding or connected to earth through a too high resistance compared with human body.
While the X capacitor may be of any practical unlimited capacitance value.
〔3〕Sub class
EN132400 divides these X and Y classifications into following a total 7 sub-classes:
3 X classes and 4 Y classes,as shown in the below table.
The required class is determined by the equipment standards for the final product.
The most popular class are X2 and Y2.
①The class of X capacitor is determined according to;
❶the equipment standard applicable to the device.
❷the peak pulse voltage to which X capacitors are exposed in operation,in addition to the rated voltage.
This kind of impulse can be caused by lightning in overhead cables,switching surges in neighbouring equipment or in the device in
which the capacitor is used to suppress interferences.
❸the "installation category" meaning the type of connection to the AC line.
Installation category Ⅱ:connection to ordinary wall outlets
Installation category Ⅲ:connection to main power trunk lines within a building.

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General technical information of (RFI/EMI)Noise suppression capacitors on AC mains

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Sub-

Peak pulse volt IEC60664

class

in service