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Mica, Glass-Epoxy, Durostone, ManniGlas, or FST Neoprene: Choosing Arc and Fire Barrier Materials
An arc barrier and a fire barrier sound like the same part and are not. An arc barrier manages a fault event: plasma, pressure, radiant flash, and the conductive residue an arc leaves behind. A fire barrier manages combustion: ignition resistance, flame spread, and heat transmission. Some materials do both, but the specification only holds together when the drawing says which duty each layer owns.
This guide walks the six families the H-O arc flash and fire protection application page covers, ordered up its temperature ladder, with standards named by designation: IEEE C37.20.7 for arc-resistant switchgear testing, UL 94 for flammability classes, IEC 60112 for tracking, IEC 60243 for dielectric methods, ASTM D495 for dry arc resistance, and ASTM E662 / E162 for the smoke and radiant-flammability data that govern enclosed rooms.
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The ladder, from organic elastomers to mica
The parent page organizes its families as a four-step temperature ladder, and the discipline is to climb only as far as the band requires, because each family up the ladder costs more and converts harder.
Organic elastomers (FST neoprene, silicone foams) serve the lowest band in gasket and lining duty; glass-epoxy laminates carry structure into the elevated band; inorganic glass-fiber paper is non-combustible; and mica tops the ladder for arc-chute and highest-band duty. Each family's exact limits are the maker's designations on the TDS, not numbers anyone invents.
Muscovite and phlogopite mica: the chute materials
The arc chute is the hardest material assignment in the breaker: its plates face the interrupting arc directly, splitting and stretching it until it extinguishes. Muscovite mica sheet in FR / arc-rated grades is the standard answer, inorganic, non-carbonizing, and dimensionally stable through repeated thermal shock, in rigid plate for structural chute walls and flexible sheet where the geometry curves. Phlogopite mica is the maker-designated step up where the chute zone runs hotter than muscovite's class.
The two converted forms are not interchangeable: rigid plate machines and die-cuts but does not bend; flexible sheet conforms but does not carry structural load. Mica barrier sheet carries the same inorganic duty outside the chute: compartment liners and high-temperature barrier plates.
Glass-epoxy laminates: the structural barrier default
Phase barriers bolt to the frame, span unsupported widths, take the pressure pulse of a fault, and sometimes carry bus supports, which makes them laminate territory. Glass-epoxy laminate covers the volume duty: G10 for the general case, FR4 where the program wants the UL 94 V-0 class on the TDS, and G11 where the maker's elevated-temperature designations apply.
H-O waterjet-cuts and machines these laminates with finished edges so cut fibers do not wick moisture; rigid-sheet test methods are standardized in ASTM D229 and the IEC 60893 family on the makers' TDS.
Durostone composite: the arc-resistant structural step up
Durostone composite (UPM 203, UPM S16) is the arc-resistant structural isolation material, carrying UL 94 V-0 file classes and IEC 60112 comparative-tracking data on its TDS, with IEC 60243 dielectric data and the mechanical strength for carrier plates and supports around the chute. It is the answer when a phase barrier's environment is polluted or condensing and the tracking line on the TDS matters more than the dielectric line.
ManniGlas glass-fiber paper: the inorganic fire side
When a fault happens, the energy has to stay in its compartment. ManniGlas glass-fiber paper (1200, 1900, 1902, 2000) is the non-combustible barrier paper for radiant-heat and compartment duty, with UL 94 V-0 file classes and ASTM C177 thermal-conductivity data per TDS, die-cut into liners, strips, and shaped barriers, flat or laminated to an adhesive for assembly. It is fire-side, not structure: where the layer also needs stiffness, a glass-epoxy backing plate carries the load.
Heat-shield silicone foam: conformable protection beside hot zones
Beside continuously hot components, the RF-120 heat-shield silicone foam pairs a conformable gasket function with heat-shield duty, reporting ASTM D1056 compression, ASTM D149 dielectric, and ASTM D495 arc-resistance data on its TDS. It serves where conformability is needed and the maker's data supports the exposure; continuous radiant zones above its band climb the ladder to the inorganic families.
FST neoprene: the enclosed-room elastomer
Inside an enclosed electrical room or any space where people work near the gear (the environment NFPA 70E governs), the question expands from "will it burn" to "what does it emit": flame, smoke, and toxicity together. The FST-rated low smoke / low flame / low toxicity neoprene (65 Shore A) carries UL 94 V-0 and ASTM E662 specific-optical-density data on its TDS, with ASTM C1166 flame-propagation testing for gasket geometry.
The V-0 silicone sponge family's super-soft grade reports ASTM E162 / E662 data, letting gasketing and barrier share one documentation story; the inorganic families sidestep the smoke question by not burning.
Barrier Families on the Temperature Ladder
| Family | Duty | Structural? | Documentation on TDS | Typical role |
|---|---|---|---|---|
| FST neoprene + silicone foams | Fire-side, gasket band | No | UL 94 V-0; E662 smoke data | Enclosed-room gaskets and linings |
| Glass-epoxy G10 / FR4 / G11 | Both, within class | Yes | IEC 60243 dielectric; FR4 carries V-0 | Phase barriers, baffles, backing plates |
| Durostone composite | Arc-side structural | Yes | UL 94 V-0; CTI per IEC 60112 | Arc-resistant isolation, carrier plates |
| RF-120 heat-shield foam | Fire-side, conformable | No | ASTM D495 arc data; D149 dielectric | Shields beside hot components |
| ManniGlas glass-fiber paper | Fire-side, inorganic | No | UL 94 V-0 file class; ASTM C177 data | Radiant and compartment barriers |
| Muscovite / phlogopite mica | Arc-side, top of ladder | Rigid plate forms | Inorganic, non-carbonizing per maker designations | Arc chutes, splitters, highest-band barriers |
Illustrative and relative only; confirm each grade on its current technical data sheet. The ladder is ordered per the makers' designations; this article quotes no invented temperature limits.
Two questions that cut the list in half
First: does the barrier carry load? Laminates machine cleanly, hold threads, and keep their stiffness; papers and foams line, wrap, and shield while something else carries the load. Second: is the exposure continuous or fault-event-only? Organic materials, including good flame-retardant grades, age fast under continuous radiant load even when they never ignite, because a flammability class describes behavior in a flame test, not longevity under radiation. Both answers belong on the drawing, and both change the family before any data sheet is opened.
How H-O Products helps
H-O Products die-cuts, waterjet-cuts, and converts; we do not manufacture laminate, mica, paper, or elastomer in-house. What we do in Winsted, Connecticut is precision conversion to your drawing: mica chute plates die-cut or machined to the chute geometry, laminate barriers waterjet-cut with clean edges, glass-paper liners cut flat or laminated to adhesive, and FST gasketing converted with the maker's documentation carried on the order, under our ISO 9001:2015 certified quality management system, with material traceability and lot-code TDS records.
Frequently asked questions
What material is used for arc chutes in medium-voltage breakers?
Mica, and it has been for decades: muscovite mica sheet in FR / arc-rated grades for the standard duty, phlogopite where the maker's high-temperature designations demand more headroom. The material is inorganic enough not to burn, dimensionally stable through repeated thermal shock, and free of carbonizing binders that would leave a conductive track behind. Rigid plate serves structural chute walls; flexible sheet serves curved splitter geometry; the two forms are not interchangeable.
What is the difference between an arc barrier and a fire barrier?
An arc barrier manages a fault event: plasma, pressure pulse, radiant flash, and conductive residue; its key properties are arc resistance (ASTM D495), tracking resistance (IEC 60112 CTI), and dimensional stability under thermal shock.
A fire barrier manages combustion: ignition resistance, flame spread, and heat transmission; its key properties are the UL 94 class per TDS, non-combustibility, and thermal conductivity (ASTM C177 on the glass-paper TDS). Mica and Durostone are arc-side; ManniGlas is fire-side; glass-epoxy laminates serve both within their classes.
Do these materials make my switchgear arc-resistant per IEEE C37.20.7?
No single material does. IEEE C37.20.7 is a guide for testing complete switchgear assemblies for resistance to internal arcing faults; the accessibility-type designations the industry quotes (including Type 2B for designs maintaining protection with a low-voltage compartment door open) belong to tested designs, not to materials.
The families on this page are what those designs are built from, and H-O converts them to your drawing with the maker's documentation. Arc-resistance claims stay with your assembly test reports; material claims stay with the TDS.
When does smoke and toxicity (FST) data matter, and which materials carry it?
Whenever the space is enclosed or occupied: electrical rooms, substation basements, walk-in gear, the NFPA 70E work context. A material can hold a respectable flammability class and still fill a room with smoke, so the FST lines belong in the callout: ASTM E662 specific optical density and ASTM E162 radiant-panel data as reported on the TDS. The FST neoprene reports E662 with UL 94 V-0; the super-soft V-0 silicone sponge grade reports E162 / E662; the inorganic families sidestep the question by not burning.
Get an arc and fire barrier recommendation
Tell us the duty (arc-side or fire-side), the structural role, the temperature band and whether exposure is continuous or fault-event-only, and any UL 94, CTI, or FST requirement, and we will recommend a family and grade direction and quote converted parts to your drawing.
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.
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Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- IEEE C37.20.7 (guide for testing switchgear rated up to 38 kV for internal arcing faults; assembly-level); IEC 62271 (HV switchgear and controlgear); NFPA 70E (electrical safety in the workplace).
- UL 94 (flammability classes, per grade TDS); IEC 60112 (comparative tracking index); IEC 60243 (dielectric methods); ASTM D495 (high-voltage low-current dry arc resistance).
- ASTM E662 (specific optical density of smoke); ASTM E162 (surface flammability under radiant heat); ASTM D229 / IEC 60893 (rigid laminate methods); ASTM C177 (thermal conductivity, glass-paper TDS).
- Manufacturer technical data sheets: muscovite and phlogopite mica, glass-epoxy laminates, Durostone composite, ManniGlas glass-fiber paper, heat-shield silicone foam, FST neoprene.
This article summarizes arc and fire barrier material-selection principles using the families, ladder ordering, and published methods cited on the parent application page. Comparisons are qualitative; classes and values are per each grade's current technical data sheet, temperature bands follow the makers' designations, and no invented limits are stated. Arc-resistance ratings belong to complete assemblies tested under IEEE C37.20.7, not to materials.
All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a converter, not a raw-material producer, and does not certify finished switchgear.