X-Capacitor (Line-to-Line): Capacitance Range 0.001μF to 10μF

Q: What is the difference between X and Y capacitors?

X-capacitors are connected line-to-line or line-to-neutral to suppress differential-mode EMI, while Y-capacitors are connected line-to-ground to suppress common-mode EMI. X-capacitors have lower safety requirements for failure (short-circuit risk), whereas Y-capacitors must fail open-circuit to prevent electric shock.

Q: How do I select an X-capacitor for an EMC filter?

Consider: 1) Required capacitance based on EMI frequency spectrum, 2) AC mains voltage rating (e.g., 250VAC for 230V systems), 3) Safety class (X2 for general applications, X1 for high-impedance or industrial environments), 4) Temperature stability for operating conditions, and 5) Compliance with regional safety standards (IEC/UL/EN).

Q: What happens if an X-capacitor fails?

X-capacitors are designed to fail safely, typically as a short-circuit initially, which may blow a fuse or trip a circuit breaker. Modern metallized film capacitors have self-healing properties that can clear minor faults, but sustained overvoltage or overheating can lead to permanent short-circuit or open-circuit failure, reducing EMI suppression effectiveness.

Component Specifications

Definition

An X-capacitor (also called line-to-line capacitor) is a safety-rated capacitor connected between live conductors (line-to-line or line-to-neutral) in electrical circuits. It suppresses differential-mode electromagnetic interference (EMI) by providing a low-impedance path for high-frequency noise currents to return to their source, preventing propagation through power lines. These capacitors must meet stringent safety standards due to their connection across AC mains.

Working Principle

Operates by capacitive reactance (Xc = 1/(2πfC)), which decreases with increasing frequency. At high frequencies (EMI range), the capacitor presents low impedance, shunting noise currents away from sensitive equipment. For differential-mode noise (between lines), X-capacitors provide a preferential path for noise currents to circulate locally rather than radiating or coupling into other circuits.

Materials

Metallized polypropylene film (MKP) or ceramic dielectric (Class X1/X2 rated), with self-healing properties; epoxy resin encapsulation; copper or tinned copper leads; flame-retardant plastic case (UL94 V-0 rated).

Technical Parameters

Parameter	Typical range	Notes & selection driver
Tolerance	±10% to ±20%
Rated Voltage	250VAC to 440VAC (X2: 275VAC, X1: 760VAC)
Impulse Voltage	2.5kV to 4kV (X2), 4kV to 6kV (X1)
Leakage Current	<0.5mA at 230VAC/50Hz
Safety Standards	IEC 60384-14, UL 60384-14
Capacitance Range	0.001μF to 10μF
Temperature Range	-40°C to +110°C
Dissipation Factor	<0.001 at 1kHz
Insulation Resistance	>10,000MΩ

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

IEC 60384-14, UL 60384-14, EN 60384-14, GB/T 6346.14

Parent Products

This component is used in the following industrial products

Input Filter (EMC Filter)

An electromagnetic compatibility filter designed to suppress conducted electromagnetic interference (EMI) entering or leaving a device via the DC input power lines.

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Engineering Analysis

Risks & Mitigation

Electrical shock if improperly rated or installed
Fire hazard from short-circuit failure
EMC non-compliance if underspecified
Reduced filter performance from aging or temperature drift
Leakage current exceeding safety limits

FMEA Triads

Trigger: Overvoltage transients (lightning, switching surges)
Failure: Dielectric breakdown leading to short-circuit
Mitigation: Use X1-class capacitors for high-impedance environments; incorporate surge protection devices (MOVs); design with derated voltage (e.g., 275VAC capacitor for 230VAC line)

Trigger: Thermal stress from high ambient temperature or ripple current
Failure: Capacitance drift or open-circuit failure
Mitigation: Select capacitors with high-temperature rating (≥105°C); ensure adequate ventilation; calculate and limit ripple current; use capacitors with low ESR

Trigger: Mechanical damage during assembly
Failure: Cracked casing leading to moisture ingress and corrosion
Mitigation: Follow manufacturer's mounting guidelines (lead bending radius); use strain relief; apply conformal coating in humid environments; implement visual inspection

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Capacitance tolerance typically ±10% or ±20%; voltage derating of 20-50% recommended for reliability; leakage current must comply with IEC 60950-1 (<0.25mA for IT equipment)

Test Method

Safety testing per IEC 60384-14 (endurance, humidity, solderability); electrical testing (capacitance, dissipation factor, insulation resistance at 500VDC); impulse voltage test (10 pulses at specified voltage); flammability test (UL94 V-0)

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of X-Capacitor (Line-to-Line)

Manufacturer profiles associated with X-Capacitor (Line-to-Line).

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the difference between X and Y capacitors?