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How to Spec an EMI Shielding Gasket: What to Send H-O for a Quote
EMI gaskets attract underspecified RFQs because the part looks like a rubber picture frame. What the quote actually prices is the joint: the field the gasket must hold off and at what frequency, the metal it must not corrode against, the force the latch can really deliver, and the environment that will spend years trying to undo all of it.
This is the ten-item checklist the H-O applications team works from for switchgear doors, VFD cabinets, rack panels, and ground pads, drawn from the parent application page's own engineering-review list, plus what engineering does with each item and what comes back.
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The ten things to send, and what each decides
| Send this | What it decides |
|---|---|
| 1. SE target and its frequency band | The family tier. A single dB number with no frequency is not yet a spec: nickel-graphite covers most sub-1 GHz commercial work, and the QPL silver-filled grades hold the band where high-frequency content dominates. |
| 2. Governing standard context | FCC Part 15 / CISPR 11 / CISPR 32 emissions, MIL-STD-461, or a customer IEEE Std 299 enclosure protocol; and whether MIL-DTL-83528 QPL traceability is a contract requirement. |
| 3. Housing metal and plating | Galvanic compatibility: silver-aluminum filler on aluminum, silver-copper reserved for tin- or zinc-plated steel and stainless, nickel-aluminum corrosion-resistant grades for marine duty. |
| 4. Closure force and compression space | Durometer and construction: soft conductive sponge compresses at 5 to 10 psi where solid grades want roughly 20 to 40 psi, and the available groove or flange depth sets the profile. |
| 5. Where the leak is | Door perimeter, panel seam, aperture, vent pattern, or ground bond; a perimeter gasket, a foil-tape seam bridge, and a low-resistivity ground pad are different parts. |
| 6. Environment and exposure hours | Indoor, industrial, outdoor, marine (specify ASTM B117 salt-fog hours, 96 through 1000-plus, to severity), and any fuel, oil, glycol, or solvent exposure, which moves the base to fluorosilicone. |
| 7. Flammability class | UL 94 V-0 on the gasket TDS is treated as non-negotiable inside VFD and drive cabinets; the class belongs to the grade, and the TDS stays with the order file. |
| 8. Door cycle count and set expectation | Hinged switchgear doors see thousands of cycles over a 25 to 40 year life; the parent page targets compression set under 25 percent per ASTM D395 for hinged-door service. |
| 9. Geometry: DXF, STEP, or PDF, or a sample part | The die program, corner engineering, and form factor: die-cut sheet for flat-faced doors, with extruded profiles coordinated through a partner network where slot retention is the right call. |
| 10. Prototype and production volumes | Converting method and price structure. Every part is made to order; prototype quantities through full production runs are equally accepted, and MOQ varies by material and part. |
What engineering does with the list
Items 1 and 2 set the performance tier: the nickel-graphite standard family (MIL-DTL-83528 Type M, 0.07 to 0.125 ohm-cm per ASTM D991) for cost-controlled commercial cabinets, or the QPL silver-filled grades (0.001 to 0.0015 ohm-cm) where the target passes 110 dB or traceability is contractual. Item 3 picks the filler chemistry against the housing; item 6 can override it toward the nickel-aluminum corrosion-resistant grades or the fluorosilicone bases.
Items 4 and 5 pick the construction: solid elastomer, soft conductive sponge for stamped surfaces and light latches, conductive foil tape for removable-cover seams and rack-bay bridging, or a low-resistivity ground pad where item 5 says the job is DC contact resistance under bolt torque. Item 7 filters to the V-0 fire-rated family where the cabinet demands it; item 8 frames durometer against cycle count. Items 9 and 10 become the die program and the price structure, and the reply cites each recommended grade's TDS values with the test method named.
What happens after you send it
- Drawing review. Engineering reviews the call-out against the vendor TDS: SE target and frequency band, gasket compression, housing-metal galvanic compatibility, fuel and solvent exposure, and UL flammability rating.
- Material direction and quote. A family and grade direction with the TDS attached, the form factor (die-cut sheet, sponge, foil tape, or partner-network profile), and pricing at your quantities.
- Samples. Typically 3 to 5 business days for common die-cut configurations on materials we keep on hand.
- Production. Standard runs ship about two weeks after drawing approval; expedited service is available. Ongoing parts run with material traceability and lot-code TDS records.
Documentation available on request: material technical data sheet, certificate of conformance, lot traceability, and first-article inspection, under our ISO 9001:2015 certified quality management system. H-O is a die-cut converter, not a raw-material producer or test laboratory: enclosure-level SE belongs to IEEE Std 299 measurement of the assembled enclosure, and emissions compliance belongs to the equipment program.
The mistakes this checklist prevents
| Spec mistake | What it causes | Checklist item that catches it |
|---|---|---|
| A dB number with no frequency | The cabinet passes sub-1 GHz and fails where the SiC switching and fast interconnects work | Item 1, the band attached |
| Silver-copper filler on bare aluminum | Accelerated galvanic loss; resistance climbs 10 to 100 times within 18 to 36 months outdoors | Items 3 and 6 |
| Firm gasket on a lightly latched stamped door | The joint never reaches contact pressure; the seam leaks from day one | Item 4 |
| Standard silicone in a fuel or glycol zone | Swelling, filler exfoliation, and an SE drop of 15 to 30 dB within months | Item 6 |
| "Fire-resistant" assumed instead of read | The audit finds a TDS without the UL 94 class the drive cabinet required | Item 7 plus the TDS check |
| Durometer chosen against the cycle count | Compression set thins the gasket; SE drops 10 to 20 dB at the joint over the door's life | Item 8 |
Frequently asked questions
What is the single most useful sentence an EMI RFQ can contain?
The SE target with its frequency band and the housing metal, together: for example, a stated dB target across a stated band, on a stated plating. Those two items eliminate most of the catalog immediately, set the filler chemistry safely against the housing, and let the reply cite tested SE in the band your emissions actually occupy rather than a single number measured somewhere else.
Can H-O cross-reference the EMI grade on my print?
In most cases, yes. If your drawing calls out a conductive elastomer, sponge, or foil tape by a brand part number, engineering identifies a comparable grade from the lines we convert, matching on filler chemistry, volume resistivity per ASTM D991, durometer, SE band, environment, and UL flammability rating. It is an industry cross-reference, not a guaranteed drop-in, verified against the vendor TDS for your application before quoting.
Does H-O stock these materials, and what is the lead time?
Every gasket is made to order to your drawing, including samples. We maintain working material relationships with the conductive-elastomer and tape manufacturers and keep some raw material on hand for faster turnaround: samples typically ship in 3 to 5 business days for common die-cut configurations, standard production runs about two weeks after drawing approval, and expedited service is available. MOQ varies by material and part.
Do I need an extruded profile or a die-cut gasket?
By retention and geometry. Die-cut sheet gaskets serve flat-faced doors, covers, and ground pads, and are H-O's core conversion, with engineered corners and PSA backing where the assembly wants it. Slot-mounted retention calls for an extruded D-profile or O-profile, which H-O coordinates through a partner network alongside the converted parts. Send the joint cross-section and the answer falls out of the drawing review.
Send the checklist, get an EMI gasket quote
Attach the geometry and as many of the ten items as you have. If something is unknown, say so; the review proceeds with the assumption flagged.
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; standard production runs about two weeks after drawing approval; expedited service is available. MOQ varies by material and part.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
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Send H-O your drawing or describe the part—engineering reviews every RFQ and converts samples on your geometry.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- MIL-DTL-83528 / SAE-AMS-DTL-83528 (conductive elastomer types and QPL); IEEE Std 299 (assembled-enclosure SE measurement).
- FCC Part 15 Subpart B, CISPR 11, CISPR 22 / CISPR 32 (emissions limits); MIL-STD-461 (military EMC); IEC 61439 (LV assemblies).
- ASTM D991 (volume resistivity); ASTM B117 (salt spray); ASTM D395 (compression set); UL 94 (flammability classes, per grade).
- Manufacturer technical data sheets and third-party MIL-DTL-83528 test reports cited on the parent application page.
This checklist supports a quotation workflow; it does not constitute design guidance for any specific enclosure. Shielding effectiveness belongs to the assembled enclosure per IEEE Std 299 and emissions compliance to the equipment program; grade-level values are confirmed on the manufacturer's current technical data sheet at quote time. All parts are custom manufactured to order; minimum production run quantities vary by material and part.
H-O is a die-cut converter, not a raw-material producer or test laboratory, and does not certify finished enclosures.