Feed Through Capacitor

10 µF Feed-Through Capacitor for MIL-STD and DO-160

What Is a Feed-Through Capacitor?

A feed-through capacitor is a three-terminal filtering device designed to allow power or signal conductors to pass through a shielded barrier — such as a metal enclosure wall or equipment chassis — while simultaneously suppressing high-frequency electromagnetic interference (EMI). Unlike conventional two-terminal capacitors, the feed-through design features a central conductor that passes directly through the capacitor body, with the outer electrode grounded to the enclosure. This coaxial structure creates a very low-inductance path to ground for RF noise, enabling effective filtering from low frequencies well into the hundreds of megahertz range.

The feed-through capacitor functions as a low-pass filter: it allows DC and low-frequency AC power to pass through unimpeded while shunting unwanted high-frequency noise currents to ground. Because the conductor physically passes through the capacitor, parasitic inductance is minimized — a critical advantage over standard bypass capacitors, which lose filtering effectiveness at higher frequencies due to lead inductance. This makes feed-through capacitors essential in environments where strict EMI control and shielding integrity must be maintained.

How Is It Used in EMC Test Setups?

Feed-through capacitors with a value of 10 µF are specifically designed for use in RFI/EMI test setups governed by standards such as MIL-STD-461 (Revisions A through G) and MIL-STD-462A. Many other standards, including RTCA DO-160G (Sections 20–22), now require their use as well. In these test configurations, the 10 µF feed-through capacitor serves two critical functions:

1. Low RF Impedance Across the Power Source: The capacitor is placed across the power supply feeding the Equipment Under Test (EUT). It provides a low-impedance path to ground for high-frequency noise, ensuring that EMI currents produced by the EUT can be accurately measured using a current probe — such as Com-Power Model CLCE-438 or CLCE-452 — without interference from the power source itself.

2. Supplemental Filtering with LISNs: When used in conjunction with a Line Impedance Stabilization Network (LISN) — such as Com-Power’s LI-4xxx or LI-3xxx series — the feed-through capacitor provides added filtering and impedance stabilization. In MIL-STD-461 Revision C setups, the 10 µF capacitor and a clamp-on current probe form the primary measurement path for conducted emissions tests (CE01/CE03). In Revisions D through G, while LISNs handle the primary measurement (CE102), the feed-through capacitor continues to serve as a bypass element to compensate for LISN inductive reactance at higher frequencies, particularly during conducted susceptibility tests (CS101).

Additional Applications

Beyond EMC test setups, the 10 µF feed-through capacitor can be permanently installed on the wall of a shielded enclosure, screen room, or equipment cabinet to function as a power-line filter. It provides adequate insertion loss — compliant with SAE ARP936 Rev. B requirements as measured per MIL-STD-220 — without suffering the power current saturation limitation that affects conventional filters employing toroidal inductors. This makes it suitable for both temporary test configurations and permanent installations where continuous high-current power filtering is required.

Typical Test Setup Diagram

CFT-10U Specifications

Key Design & Safety Features

• Built-in Bleeder Resistor: A 1.5 MΩ parallel bleeder resistor is incorporated internally to safely discharge the capacitor when the applied voltage is removed, meeting safety requirements for test environments.
• High Current Capacity: The M6 x 1.0 threaded feed-through studs accommodate 100 Amps of continuous current without heating or voltage loss, making the capacitor suitable for high-power EUT supply lines.
• No Saturation Limitation: Unlike filters that use toroidal inductors, the feed-through capacitor does not suffer from power current saturation, ensuring consistent insertion loss performance regardless of load current.
• ARP936 Compliant Insertion Loss: Meets SAE ARP936 Rev. B insertion loss requirements as measured per MIL-STD-220, ensuring reliable filtering performance across the required frequency range.
• Rugged Construction: CRCA and brass/nickel-plated construction with UL94 V-0 rated insulation provides durability and flame resistance for use in shielded enclosures, screen rooms, and equipment cabinets.

Compatible Com-Power Products