EMI Filters from Captor Corporation

EMI FiltersCaptor Corporation is the most trusted name in EMI filters. We specialize in supplying standard and custom-tailored EMI filters at competitive prices without sacrificing quality or performance.

Most electric and electronic devices—such as motors, power supplies, and microprocessors—generate some degree of high-frequency electromagnetic noise. Although a common issue, the noise produced can prove to be problematic, especially in critical operations, as it degrades the quality of signal and power transmissions.

Electromagnetic interference (EMI) filters are one solution industry professionals employ to mitigate the effect of electromagnetic noise on power and signal lines. By using the devices in their electrical and electronic equipment, they enhance system performance by redirecting and reducing the noise by canceling or grounding the line.

EMI Filter CAD Catalog

Standard EMI Filters From Captor Corporation

At Captor Corporation, we offer a broad selection of off-the-shelf EMI filters suitable for use in a wide range of general and industry-specific applications. Boasting durability, reliability, and industry-leading performance at a competitive price, our standard product lines are up to almost any EMI filtration challenge. Our standard EMI filter offerings include:


DC EMI filters: Our DC EMI filters are rated for voltages of 0 to 400 VDC and currents ranging from 1 to 25 A.


AC three-phase EMI filters: Our AC three-phase EMI filters are rated for voltages of 120/208 VAC at 50/60 Hz and 400 Hz and currents ranging from 1 to 25 A.


AC three-phase with filtered neutral EMI filters: Our AC three-phase with filtered neutral EMI filters are also rated for voltages of 120/208 VAC at 50/60 Hz and 400 Hz and current ranging from 1 to 25 A.


AC single-phase EMI filters: Our AC single-phase EMI filters are rated for voltages of 125/250 VAC at 50/60 Hz and 400 Hz and currents ranging from 1 to 25 A.


Circuit card assembly (CCA) mounted EMI filters: MIL-STD-461 guidelines are among the most stringent, and it can be difficult to find a compliant DC-DC converter. We offer several EMI filters that meet compliance requirements. Additionally, we can custom design a filter to suit unique voltage, current, and size specifications.

Our standard EMI filters feature the following:

  • Insulation resistance: minimum of 1,500 MΩ
  • Insertion loss: 1000 VDC for line-to-line and line-to-chassis
  • Voltage drop: Less than 1% of the rated voltage
  • Terminal strength: Complies with MIL-STD-202, Method 211
  • Operating temperature range: -55º C to 71º C
  • Storage temperature range: -55º C to 105º C
  • Terminal threading: 10-32UNF-2A
  • Insert threading: 10-32UNF-2B
  • Bracket mounting holes: 203-inch diameter
  • Chassis material: Cold rolled steel
  • Chassis and terminal finish: Electro tin-lead

Custom EMI Filters From Captor Corporation

Our team fully understands that an off-the-shelf solution may not be right for every customer. Fortunately, as experts in electromagnetic interference filtration, we have the knowledge and skills to design and build custom EMI filters to meet unique needs.

We provide full-service custom solutions, offering customer support from project concept to project completion. Our services include design and analysis of the filter circuit, design and layout of the packaging, prototyping, and testing, all of which are optimized to deliver the highest quality at the best possible price. We accommodate custom filter designs with voltage ratings between 0 to 400 VDC and 0 to 480 VAC, current ratings between 0 to 400 A, and frequencies up to 400 Hz. Higher ranges are also available upon request.

Having successfully completed over 10,000 custom filter designs to date, with many of them proving more cost-effective than catalog items, we’ve demonstrated ourselves as one of the leading suppliers of custom EMI filters. Our electromagnetic, power line, signal line, HEMP, and TEMPEST filters are guaranteed to offer reliable performance for their entire working life, which is why we have thousands of satisfied customers across the military, aerospace, commercial, and industrial sectors.

EMI Filter FAQ

How Do EMI Filters Work?

EMI filters exist as separate or integrated devices in electrical and electronic equipment. In simplest terms, within such equipment, they act as low-pass filters for unwanted—generally high-frequency—current. They consist of passive electrical components—including inductors and capacitors—that, when assembled together, form a complete LC circuit. The inductor component allows low-frequency and DC currents to pass through uninhibited and blocks high-frequency current (i.e., the noise). Once blocked, the low impedance path provided by the capacitor component directs the noise back into the power supply or a grounded connection.

Since EMI filters are only capable of diverting conducted interference, the devices are often combined with shielding and insulation components to block radiated noise that travels through the air. Radiated interference is especially a concern when there is a significant length of conductor between the filter and the interference source. If there is only a short length of wire between the filter and the noise source, the EMI filter alone may suffice.

What Are the Dangers of EMI?

The consequences of EMI have a significant impact on many industries, causing various issues such as data loss, downtime, and permanent damage. When electronic systems do not have adequate noise reduction, there is an increased risk for interference, which can cause hazardous interruptions in vulnerable devices such as mission-critical military equipment, life-sustaining medical equipment, and more.

In the military and defense sector, EMI filtration is vital. Ambient noise can interrupt military equipment that is essential to operations. There is also a risk of the weaponization of EMI, known as high altitude electromagnetic pulses (HEMP). EMI sources and HEMP threats can lead to sensitive data loss and the disruption of military operations or communications.

Why Are EMI Filters Important?

Where Does EMI Come From?

A variety of sources produce EMI, and the presence of EMI grows as the use of various technologies increases. As more electronics power on, electrical noise becomes more prevalent. There are three types of EMI sources, and they include:

  • Electronic. High-frequency noise is an unavoidable by-product of electronic technology. Equipment such as transmitters, igniters, power lines, electrical collectors, and generators produce a significant amount of EMI, which can degrade device operations.
  • Inherent. Thermal agitation, which refers to electrons moving through a circuit resistor, produces EMI within electronic devices.
  • Natural. Natural EMI results from natural events such as electrical storms, solar radiation, rainstorms, and snowstorms. Modern electronics are resilient to natural EMI, but older RF communications equipment may experience interference. This type of interference is often known as atmospheric noise.

EMI is caused by both residential and industrial sectors. Residential EMI typically disrupts or degrades signal without causing permanent damage to electronics. Appliances and wireless devices used by the typical consumer generate this type of interference. Some residential sources of EMI include cellular phones, microwaves, electric blankets, laptops, and more.

Industrial EMI can cause lasting and significant interference in essential electronics and may result in large-scale impacts. Industrial EMI produces ambient electromagnetic energy, which can interfere with local power grids, medical devices, and military operations. Common causes include television transmissions, electric motors and generators, radio and satellite, and more.

What Are the Applications of an EMI Filter?

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Applications of an EMI Filter

A variety of applications depend on EMI filters for uninterrupted function. It is essential to consider the application when choosing the correct EMI filter to prevent interference and produce the expected results. Common types of EMI filters include:

  • Consumer Electronics. EMI filters for consumer electronics subdue electromagnetic noise for numerous household devices, such as washing machines, treadmills, and other appliances. These filters protect against EMI damage while ensuring that consumer electronics meet electromagnetic compatibility standards.
  • Single-phase. Small industrial and residential equipment rely on single-phase EMI filters to prevent noise. Common applications include small electronics and appliances, food service equipment, and more.
  • Three-phase. Industrial equipment, motors, medical devices, and test equipment rely on three-phase EMI filters for robust noise suppression in industrial applications. These filters have a three-stage filtering system for optimal EMI filtration.
  • Military EMI Filters. Aerospace and military communication systems rely on military EMI filters to protect against damage caused by high-frequency noise and HEMP interference. These filters must meet strict standards and comply with military regulations.

Where Should an EMI Filter Be Placed?

Placing the EMI filter where it is most beneficial to the application is key to getting the best protection. The most advantageous location for a mains or power line EMI filter is typically at the power entry point of the newly installed equipment. This location prevents high-frequency noise from entering or exiting the equipment.

What Is the Difference Between EMC and EMI?

It is critical to consider not only EMI but also electromagnetic compatibility (EMC) when installing electronics. As mentioned above, EMI refers to electromagnetic noise that can disrupt the operations of RF systems and electronic devices. Types of EMI include conducted, common mode, radiated, and differential mode.

EMC is an electrical component’s ability to withstand electromagnetic interference while operating, as well as its ability to not generate additional EMI that could interfere with nearby devices. Incorporating EMI prevention can enhance a product’s EMC, along with shielding and EMI filtering.

Industries and regulatory groups worldwide provide standards for EMC and EMI compliance. Military standards require rigorous testing for compliance under MIL-STD 464 and MIL-STD 461. Industry regulators make standards for industry-specific applications, and governing bodies like ISO provide standards and testing criteria. Testing for compliance must include both emissions and immunity to cover the device’s susceptibility to EMI and ensure EMI emanating from the device stays within specific limits.

To learn more about the differences between EMC and EMI, please visit our blog.


EMI Filter Capabilities

Insertion Loss / Attenuation

0 to 100 dB

Voltage Rating

0 to 400 VDC
0 to 480 VAC
Higher Voltage rating available upon request


0 to 400 Amps
Higher Currents available upon request


DC to 400 Hz
Other frequencies available upon request

Typical Operating Temperature

-55 to +71 °C

Higher temperatures available upon request.

Typical Storage Temperature

-55 to +105 °C

Higher temperatures available upon request.



Chassis Material

CRS, Brass, Aluminum, Stainless Steel


100% Test


Temperature Cycling
Temperature Shock

Quality Control

Test Plan
Test Report

Secondary Operations (In-House)

Quick Turn Prototypes

Production Volume

Prototype to Large Scale Production Runs

Typical Lead Times

1 week (Stock)
10 to 12 weeks (Custom)
1 to 3 weeks (Prototypes)

Additional Information

Industry Focus


Industry Standards

AS9100 Rev D
ISO 9001:2015
IPC 610
IPC 620

File Formats

PCAD (Circuit Boards)

Contact the EMI Filter Experts at Captor Today

Electromagnetic interference significantly affects the performance of electrical and electronic equipment. EMI filters enable industry professionals to mitigate the effect of noise, resulting in better quality signal and power transmissions. If you need EMI filters for your facility, turn to the experts at Captor. At Captor Corporation, our standard and custom solutions offer the durability, reliability, and performance needed to optimize electrical and electronic equipment operations. For additional information about our standard filter products or our custom filter capabilities, contact us or request a quote today.

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