Custom EMI/RFI Shielding Gaskets for Switchgear, VFD Enclosures & Power Cabinets

Shielding effectiveness (SE) is the ratio of incident-to-transmitted RF field amplitude across an enclosure wall or gasket joint, expressed in decibels per the 20·log₁₀ convention used in MIL-DTL-83528 and IEEE Std 299 (so 20 dB = 10× field-strength reduction, 60 dB = 1,000×, 100 dB = 100,000×).

SE is frequency-, geometry-, and material-dependent: per third-party MIL-DTL-83528 test reports, premium QPL silver-filled silicones (SSP2569-65 Type A, SSP2368-65 Type B) hold > 110 dB across the full 20 MHz–10 GHz E-field band; nickel-graphite SSP502 grades typically deliver > 100 dB sub-1 GHz with modest variation through 10 GHz; carbon-filled and lossy materials roll off more steeply above 1 GHz.

Industry-typical targets (geometry- and test-method-dependent): commercial switchgear and motor-control-center cabinets aim for 60–80 dB at the dominant emission band per CISPR 11 / FCC Part 15; military and aerospace assemblies target 80–100 dB per MIL-STD-461. Server racks and data-center applications typically need 60–80 dB across the full GPU-cluster band (sub-1 GHz through 6 GHz). Don't extrapolate from a single dB number on a TDS.

Demand the full frequency-response curve and specify the SE target at the frequency band that matters for your application. [3]

SSP502 is a firmer-durometer solid nickel-graphite-filled silicone elastomer (non-QPL commercial nickel-graphite), the production-volume standard for hinged-door perimeter EMI gaskets where the mating surface is reasonably flat (machined or precision sheet) and the clamp force is consistent. BISCO® EC-2130 is a softer (30 Shore A) electrically soft conductive solid silicone, also nickel-graphite-filled per the material TDS Publication #180-034.

Specify it when the mating surface is irregular (stamped sheet, rolled-form bend), when low closure force is required (5–10 psi instead of SSP502's 20–40 psi), or when both EMI shielding and modest environmental sealing are needed at the same joint.

The two are not interchangeable: SSP502 delivers higher SE at higher frequency at the cost of higher closure force; EC-2130's sponge structure conforms to imperfect surfaces at lower closure force. Volume resistivity per the material TDS is < 1.00 Ω·cm for EC-2130 vs typical 0.07 Ω·cm for SSP502-65 standard nickel-graphite per SSP TDS. For high-cycle hinged doors with flat machined mating surfaces, SSP502.

For stamped sheet metal panels, removable covers, or door designs with tolerance variation, EC-2130. For 0.001–0.002 Ω·cm volume resistivity on mil/aero spec, see the QPL silver-filled SSP2368-65 (Type B Ag/Al) or SSP2569-65 (Type A Ag/Cu). [2]

Both are BISCO® products but they target different applications per the the material TDSs. EC-2130 (Publication #180-034) is a 30 Shore A nickel-graphite-filled soft conductive solid silicone, volume resistivity < 1.00 Ω·cm, shielding effectiveness 103–110 dB across 100 MHz–10 GHz, UL 94 V-1 at 3.2 mm thickness (HBF at 1.6 mm). It is the right call for perimeter EMI gaskets on irregular mating surfaces.

EC-2265 (Publication #180-359) is a 65 Shore An electrically conductive solid silicone with carbon-black filler, volume resistivity 5 Ω·cm per ASTM D991, no UL 94 rating listed. the manufacturer’ published application is "low amperage conductor and protection against electrostatic discharge". EC-2265 is an ESD-protection grade, not a low-resistance EMI ground-bond product.

For true low-resistance bolted ground bonds, specify SSP2569-65 Type A Ag/Cu silicone (0.0015 Ω·cm), SSP2368-65 Type B Ag/Al silicone (0.001 Ω·cm), or copper foil tape.

[2]

Galvanic corrosion is the electrochemical attack that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (moisture, salt, condensation). At an EMI gasket joint, the conductive filler in the gasket (typically silver-coated particles) and the housing metal (typically aluminum or steel) form a galvanic couple. Over months to years of service in humid or marine atmospheres, the less-noble metal corrodes preferentially, building up insulating oxide product at the gasket-housing interface.

The result: contact resistance climbs 10–100×, SE drops 20–40 dB at the joint, and the cabinet fails periodic re-certification. Prevention starts at spec: match the filler chemistry to the housing metal. Silver-aluminum (Ag/Al) on aluminum housings is galvanically benign. Silver-copper (Ag/Cu) on bare aluminum drives accelerated loss within 6–18 months in marine atmosphere. Reserve Ag/Cu for tin-plated, zinc-plated, or stainless housings.

For marine, coastal, or salt-spray duty (NEMA 4X / IP66), specify the nickel-aluminum corrosion-resistant grades SSP2529 silicone or SSP2551 fluorosilicone, which deliver 500–1,000+ hours per ASTM B117 vs. under 96 hours for standard grades. Use our galvanic-compatibility lookup tool above to validate your combination. [6] [1]

Standard silicone EMI elastomer (SSP502 nickel-graphite silicone base) handles ambient air, water spray, ozone, and most weathering without measurable degradation. What it doesn't tolerate is sustained contact with hydrocarbon fluids: jet fuel, diesel, gasoline, hydraulic oil, mineral oil, glycol/water coolant mixtures, or aggressive solvents. In those service environments standard silicone swells 20–40%, the elastomer loses cross-link density, the conductive filler partially exfoliates, and SE drops 15–30 dB, typically within 6–24 months.

Fluorosilicone (FVMQ) uses the same general silicone backbone but with trifluoropropyl side groups that resist fluid uptake. SSP502F nickel-graphite fluorosilicone grades (502F-50, 502F-60, 502F-80) hold SE through full-life exposure to fuel, oil, glycol, and most industrial solvents. For premium silver-filled fluorosilicone (M83528 QPL Types C and D), see SSP2486-70 (Type D Ag/Al, vs the equivalent competitor QPL silicone) and SSP2573-75 (Type C Ag/Cu, vs the equivalent competitor QPL silicone).

Specify fluorosilicone when the cabinet sees any of: aircraft / military fueling environment, mobile power-distribution with fuel-vapor exposure, CDU (coolant-distribution-unit) cabinets in liquid-cooled data centers, chemical-process control cabinets, or any application where a leak in an adjacent system could wet the gasket. Don't specify it for ordinary indoor switchgear, the cost premium isn't justified.

MIL-DTL-83528 is the U.S. Department of Defense detail specification for conductive elastomer EMI gaskets. The standard defines material classes by conductive filler chemistry (silver-aluminum, silver-copper, silver-nickel, silver-glass, nickel-graphite), grades by durometer and form, and qualification tests for volume resistivity (per ASTM D991), continuous service temperature, salt-fog endurance, and fuel/fluid compatibility. Around 2017 SAE took over administration as SAE-AMS-DTL-83528 (current revision: E).

Materials “aligned to MIL-DTL-83528” means the formulation, properties, and test methods follow the standard, not that any individual lot has been qualified by a third-party test lab against the full DSCC qualification protocol. For defense and aerospace work requiring formal qualification, specify the class number explicitly (Class 1 silver-aluminum, Class 2 silver-copper, etc.) and require lot-specific qualification documentation.

For commercial switchgear and industrial work, “aligned to MIL-DTL-83528” on the H-O converted part is sufficient; specify the SSP502 grade by name and your housing-metal galvanic compatibility constraint.

[1]

IEEE Std 299 (current edition: 2006, reaffirmed 2012) is the IEEE standard method for measuring shielding effectiveness of electromagnetic shielding enclosures. It defines the test setup, antenna types, source-to-receive geometry, and frequency-discrete measurement protocol for SE measurement from 100 kHz through 18 GHz. The standard does not certify the gasket alone, it measures the assembled enclosure's SE, which is the combination of the wall material, the seam construction, the gasket choice, and the door / panel geometry.

For commercial switchgear and motor-control-center work, IEEE Std 299 testing is generally not required. CISPR 11 or FCC Part 15 emission compliance is the discriminator. For data-center, telecom, and military applications, IEEE Std 299 testing (or its companion IEEE Std 299.1 for smaller enclosures) is often part of the customer acceptance protocol. When the customer's spec calls for “60 dB SE per IEEE Std 299 at frequencies XX”, that's a measured-enclosure-level performance target, not a gasket-only material spec.

[3]

Variable-frequency drives create broadband EMI through the high-dV/dt switching events at the inverter stage. The fundamental switching frequency (typically 2–20 kHz for IGBT, 20–100 kHz for SiC) is rarely the EMC problem, the emission spectrum is dominated by harmonics of the switching edges that extend from hundreds of kHz through several GHz. For classical IGBT drives (2–8 kHz switching, 5–15 kV/µs edges), the dominant emission band is 30 MHz–300 MHz, and standard SSP502 nickel-graphite grades deliver adequate SE.

For modern SiC drives (20–100 kHz switching, 30–100 kV/µs edges) the emission spectrum extends into 1–6 GHz, and silver-copper grades (SSP2569-65 Type A or SSP2571-85 Type K, both Ag/Cu at 0.0015–0.002 Ω·cm) or knitted-wire-mesh-over-silicone composite gaskets are the right call. Also specify UL 94 V-0 for the gasket on VFD cabinets, fire-rated enclosures and arc-fault hazard zones require it.

SSP502-V0 (502-40-V0, 502-60-V0) is the standard grade for VFD perimeter EMI sealing.

Volume resistivity (Ω·cm) measures the bulk material's resistance to current flow through its thickness, under a specified compression and probe geometry per ASTM D991. It's the most spec-relevant single number for an EMI gasket, lower volume resistivity correlates with higher SE at any given joint design and clamp force.

Typical numbers per actual manufacturer TDSs: SSP502 standard nickel-graphite silicone 0.07–0.125 Ω·cm (502-65 / 502-30 per SSP TDSs); SSP2368-65 Type B Ag/Al silicone 0.001 Ω·cm; SSP2569-65 Type A Ag/Cu silicone 0.0015 Ω·cm; SSP2573-75 Type C Ag/Cu fluorosilicone 0.002 Ω·cm; SSP2486-70 Type D Ag/Al fluorosilicone ~0.008 Ω·cm; SSP2529 Ni-Al silicone ~0.020 Ω·cm; BISCO EC-2130 < 1.00 Ω·cm per Publication #180-034; BISCO EC-2265 5 Ω·cm per Publication #180-359 (carbon-black filler, ESD grade).

Surface resistivity (Ω/square) measures current flow along the surface, not through the bulk. It's relevant for ESD dissipation applications but rarely the discriminator for EMI gasket selection. DC contact resistance (mΩ at specified clamp pressure) is a third measurement, taken across the gasket-housing interface at a specific bolt torque or clamp force, this is the spec that matters for bolted ground-pad applications, and varies by material and gasket geometry.

Ask the vendor for DC contact-resistance test data at your specific clamp pressure. When in doubt, ask the vendor for volume resistivity per ASTM D991 and ignore generic “low resistivity” marketing claims. [4] [7]

UL 94 (current edition 13, June 2024 update) classifies the flammability of polymeric materials. V-0 is the highest standard rating for a sample held vertically: burning stops within 10 seconds, no flaming drips that ignite the cotton placed beneath, no afterglow beyond 30 seconds. Most VFD and drive cabinets carry a UL listing (UL 508A, UL 508C, UL 60947-4-1 for the assembly), and the listing requires that all polymer materials inside the cabinet (including EMI gaskets at panel seams) meet V-0.

The reasoning is straightforward: a VFD cabinet houses high-energy semiconductor switches and the potential for arc-fault initiation. A non-V-0 gasket can propagate a fire from an internal arc event to adjacent equipment. Always specify V-0 for VFD / drive enclosures, motor-control-centers with adjustable-speed-drives inside, fire-rated electrical-room cabinets, and any cabinet that requires UL listing with internal polymer materials. SSP502-V0 (502-40-V0, 502-60-V0) is the standard V-0 EMI gasket choice.

BISCO EC-2130 is rated UL 94 V-1 at 3.2 mm and HBF at 1.6 mm per the material TDS. Specify SSP502-V0 grades, not EC-2130, where V-0 is mandatory. [5]

Conductive foil tape (copper or aluminum foil with conductive PSA) and conductive elastomer gasket solve different mechanical problems. Foil tape is right for static seams where an elastomer can't be mechanically retained, removable cover panels, lap seams between adjacent rack bays, conductive bridges over cable feedthroughs, and EMI retrofit / repair work on existing cabinets. The foil has lower volume resistivity than any elastomer (~0.002 Ω·cm for copper) and creates an excellent low-resistance bond at the seam.

Conductive elastomer gasket is right for any joint that opens and closes (hinged doors, removable access panels with retained-screw closures, drawer fronts) because the foil's PSA bond degrades under repeated cycling and the foil itself tears at sharp bend radii. The two combine well: on a single cabinet, use SSP502 at the hinged-door perimeter (high-cycle) and copper / aluminum foil tape at the static side-panel seams (no-cycle).

For galvanic compatibility, match the foil chemistry to the housing: copper foil on tin / zinc / stainless housings; aluminum foil on aluminum housings. [9]

The applicable EMC standard depends on the equipment classification and the market. FCC Part 15 Subpart B applies to unintentional radiators in the United States, most switchgear, motor-control-centers, and industrial cabinets fall under Class A (commercial / industrial environment, looser limits) or Class B (residential, stricter limits). CISPR 11 covers industrial, scientific, and medical (ISM) equipment globally, most VFDs, motor drives, and power-conversion equipment use it as their primary EMC reference; current edition 7.0 (2024).

CISPR 22 (now superseded by CISPR 32, current edition 2.2 / 2024) covers information-technology equipment, this is the standard data-center server racks, networking equipment, and computing cabinets typically test against. Most modern equipment meets multiple standards simultaneously. For an EMI gasket spec, what matters is the frequency band and the dB attenuation target, not which standard label is on the certification.

The standards generally agree on commercial / Class A limits in the 30 MHz–1 GHz range; they diverge above 1 GHz where CISPR 32 extends emission limits to 6 GHz for high-frequency switching equipment.

[10] [11] [12]

Salt-spray (salt-fog) exposure per ASTM B117 is the industry-standard accelerated test for corrosion endurance of EMI gasket-housing combinations. The test exposes the gasket-on-housing assembly to a 5% NaCl mist at 35°C and measures the hours-to-failure, where “failure” is typically defined as either visible white corrosion product at the interface, SE drop below the design target, or DC contact resistance rise above a threshold (commonly 10× initial).

Industry-typical targets: indoor commercial cabinets (96 hours is the standard spec; outdoor industrial cabinets) 500 hours; marine / coastal / IP66 cabinets, 1,000+ hours. Silver-aluminum grades (SSP2368-65 Type B silicone for aluminum housings, SSP2486-70 Type D fluorosilicone for aluminum + fuel exposure) perform well on properly passivated aluminum housings with chromate conversion coating; the specific hours-to-failure depends on the housing-metal preparation and is documented per gasket-housing pairing on the vendor TDS / test report.

SSP's third-party ASTM B117 testing of SSP2529 nickel-aluminum silicone measured 0.08% weight loss on chromate-conversion-coated Al 6061 after 168 hours, the most conservative documented endpoint in the catalog for galvanically aggressive housings. Verify the documented hours against the SSP TDS for your specific gasket-housing combination, vendor B117 numbers are reported for one specific pairing and don't necessarily apply to a different housing metal, plating, or surface preparation.

For salt-spray durations beyond what's published on the TDS, request a project-specific qualification run from SSP through H-O. [6]

H-O is a die-cutter and converter — every EMI gasket we ship is made-to-order to your drawing, including samples and prototypes. We maintain working material relationships with SSP (HEICO) for the SSP502 nickel-graphite EMI silicone family (30, 40, and 65 Shore A standard silicone, SSP502-V0 fire-rated grades, and SSP502F nickel-graphite fluorosilicone) and with the manufacturer for BISCO EC-2130 and EC-2265 soft conductive solid.

Some raw material is held on hand for faster turnaround; the SSP MIL-DTL-83528 QPL silver-filled grades (Type A Ag/Cu, Type B Ag/Al, Type C/D fluorosilicones) are typically ordered against your specific job from SSP in Ballston Spa, NY.

Samples typically ship in 3–5 business days for common configurations on materials we keep on hand. Standard production lead time after drawing approval is 2 weeks, including die-cut, molded, and laminated configurations. QPL silver-filled grades and complex multi-layer parts run on the standard production schedule. Expedited service is available when timing is critical. MOQ varies by material and part; prototype quantities through full production runs are equally accepted.