Technical note · 2 November 2026 · EMC
Short answer: shielding effectiveness of a 19″ subrack is not set by the gasket you buy, it is set by the worst of six mechanical joints. Four of them need a gasket or a conductive surface; two are closed by geometry. Get the frame parts right and the result is predictable; add gaskets everywhere and you mostly add insertion force and cost. This note goes through the six joints one by one, with the catalogue part that closes each of them.
An enclosure is a current path, not a box. Interference couples into the seams, so the shielding effectiveness (SE) of the assembly is set by the joint with the highest transfer impedance — one screw hole without conductive contact can dominate the whole result. The mechanics of a 19″ subrack are defined by IEC 60297-3-100 / -101 and IEEE 1101.1; the shielding behaviour on top of that geometry is a matter of contact pressure, contact area and what happens to both over temperature cycles and repeated insertion.
Measurement is a separate question. For enclosures in the 0.1–2 m range, which covers our chassis, IEEE 299.1 defines the method and sets no pass limit — the frequency range and the required SE belong in the specification. A datasheet number without a standard, a distance and a frequency is decoration.
| # | Joint | Closed by | Catalogue part |
|---|---|---|---|
| 1 | Front panel to horizontal rail | Shielding strip, stainless, 10 pcs per kit | 24560-235 (84 HP, 416.56 mm) |
| 2 | Cover plate to horizontal rail | Shielding kit, stainless, 10 pieces | 24560-245 (84 HP) |
| 3 | Side panel to rear angle | Rear angle for stainless gasket (pair) | 24561-198 3 U · 24561-298 4 U · 24561-498 6 U |
| 4 | Side panel to rear angle, textile version | Rear angle for textile gasket (pair) | 24564-199 3 U · 24564-299 4 U · 24564-499 6 U |
| 5 | 19″ bracket to side panel | Bracket, rear side conductive, front anodised | 24560-197 · 24560-198 (handle holes) |
| 6 | Rail to rail, VPX systems | Cross member, M-profile and EMC combined | 34562-984 (84 HP) |
Two details decide whether these parts actually work. First, the gasket is only half of the joint: it presses against a mating surface that must be conductive. That is why the 19″ bracket is specified as rear side conductive and front anodised — anodising insulates, so the conductive side has to face the gasket, not the paint. Second, the rear angle differs between gasket types: 24561-198 takes a stainless strip, 24564-199 takes a textile gasket, and they are not interchangeable. Ordering the gasket without checking which angle is fitted is the most common mismatch we see on retrofits.
The same logic applies to guide rails: a coded EMC rail with an ESD clip provides the board-edge contact, and it has to be the rail, not a clip glued onto a plain rail, or the contact area walks out of position after a few hundred insertions. Our rail and accessory range is built on that basis.
| Stainless steel strip | Textile (fabric over foam) | |
|---|---|---|
| Contact pressure needed | Higher — the strip behaves as a spring | Lower — the foam compensates for surface flatness |
| Compression set | None in practice; recovers after opening | Takes a set if compressed hot and left closed for years |
| Repeated opening | Good, provided the strip is not deformed on assembly | Better for frequent access; the fabric wears first |
| Mating surface | Hard, machined or extruded aluminium; needs conductive finish | Forgiving on thin sheet, die-cast and plated plastic |
| Frame part | 24561-198 / -298 / -498 | 24564-199 / -299 / -499 |
| Where it is the right answer | Fixed installations, screwed covers, temperature cycling | Serviceable joints, thin housings, low insertion force |
Typical attenuation figures for conductive gaskets in this class fall in the tens of dB and depend heavily on contact pressure — public ranges of roughly 40–80 dB are quoted for the category as a whole. Treat that as an order of magnitude, not a specification, and fix the number with a test per IEEE 299.1 on the actual assembly.
Three process decisions undo a good gasket faster than any design error:
Because these are drawing-level decisions, they are the part of an EMC subrack we can control in our own plants: laser cutting, CNC punching, bending, tapping, masking, finishing and assembly are all in-house in Kunshan, with the cabinet work in Hefei. There is no subcontracted finishing step where masking instructions get lost.
Upgrading an installed subrack is usually cheaper than replacing it, because the cage geometry is already right. The work is a parts swap:
| Step | What changes | Part |
|---|---|---|
| 1 | Side panels or covers: plain to shielded | Retrofit shielding subrack kit, 3 U 295 mm |
| 2 | Rear angles for the gasket type you will use | 24561-198 / 24564-199 (3 U) |
| 3 | Panel-to-rail sealing | 24560-235 (front panel) · 24560-245 (cover plate) |
| 4 | Guide rails with ESD clips | Coded EMC rails, 160 / 220 mm |
| 5 | Conductive finish on mating faces | Masked at coating; or chromate conversion |
The 3 U kits are 24563-133 at 295 mm depth and 24563-131 at 175 mm. Both are subrack kits rather than loose parts, which matters for a retrofit: the depth and the rail positions come as one assembly instead of being re-specified part by part. Every part number here sits inside the 771-part cross-reference, so if the cage in front of you carries an incumbent brand number, that number is enough to start.
We do not publish an SE figure for a subrack, because a number without a test standard, a frequency range and a measurement distance is not comparable between suppliers. What we will do is state the mechanical facts — which joints are closed, what the contact surfaces are, what the gasket material is, and how the finish is masked — and then test the assembly with you against a specification you write. If a project requires a certified SE report, that is a test-house job on a defined sample, and we will supply the sample and the drawing package for it.
No. Four carry the current in a 19″ subrack — front panel to rail, side panel to rear angle, 19″ bracket to side panel, cover plate to rail. The other two are closed by geometry: coded EMC rails with ESD clips at the board edge, and a conductive cross member where the profile already provides contact.
Stainless for screwed assemblies that see temperature cycling: higher contact pressure, no compression set. Textile for joints opened often, thin sheet, die-cast or plated plastic. They need different rear angles — 24561-198 series versus 24564-199 series — and the two are not interchangeable.
Usually yes, and cheaper than replacing the cage. Side panels or covers, rear angles, panel-to-rail shielding strips, rails with ESD clips and a conductive finish on the mating faces. Retrofit kits come as assemblies: 24563-133 at 295 mm and 24563-131 at 175 mm depth.
Next step. Send the subrack drawing, or a photo of the rail cross-section and the rear angle, plus the frequency range you need to meet. We come back with the parts list per joint, which parts of your existing cage can be reused, and where the finishing has to be masked. Request a shielding review.
Send the cage drawing or a photo of the rail cross-section — we come back with the parts that close each joint, and which ones you can reuse.
