James discusses when and where to use X- and Y- safety capacitors. Many power supplies use these capacitors in their AC stage to shield against RFI (Radio Frequency Interference) or Electro-Magnetic Interference (EMI). The most common reason we hear for using an X2 capacitor in a smart meter design is that the designer wants “a UL rating.” The Underwriter’s Laboratories (UL) has several standards in place that must be met to attain their certification. Today, these standards are superseded by IEC 60384-14. It is important to understand what these ratings mean. For example, UL1414 is a definition for capacitors in suppression applications. Which is, capacitors placed from line to line (“X” Capacitors) and line to ground (“Y” Capacitors.)
However, these standards do not define how the capacitor should operate in an in “series coupling” application. Like we find with Smart Meter power supply designs. With that in mind, KEMET has several series that are X2-rated and are suitable for smart meters.
- UL Standards define capacitor behavior in Line to Line or Line to Ground placements
- X and Y capacitors must fail open
- Pick capacitors designed for series coupling applications
- KEMET Product Datasheets
- Smart Meter Related Content
Please note that the popular X2 Series “R46” is NOT suitable for series applications.
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