Arc Flash & Fire Protection

Mica sheet, and it has been for decades. Arc-rated muscovite mica (rigid FR plate for chute walls, flexible sheet for curved liners) is the standard duty material: inorganic, dimensionally stable through thermal shock, and non-carbonizing, so the arc leaves no conductive track behind. Where the chute zone runs hotter than muscovite's class, the maker's phlogopite grades carry the higher temperature designations. H-O die-cuts and machines both to the chute geometry, with the maker's grade designation carried on the order. [7]

All three are woven-glass epoxy laminates from the same family (NP500A / NP510A / NP511). They differ in class, not chemistry type. G10 is the general-purpose grade and serves most phase barriers and baffles. FR4 is the flame-retardant member, carrying a UL 94 V-0 class on its TDS, specify it when the program requires the class on the barrier material itself. G11 carries the maker's elevated-temperature designation for barriers near heat sources.

Dielectric data is per IEC 60243 / ASTM D229 methods on the TDS. Name the grade on the drawing; 'G10/FR4' written interchangeably is how unclassed material ends up where V-0 was required. [4]

When the part lives in or beside the arc zone and needs tracking resistance and a V-0 class together with structural strength. Durostone UPM 203 and UPM S16 carry UL 94 V-0 file classes and comparative-tracking (CTI) data per IEC 60112 on their TDS, which is the combination arc-resistant structural isolation wants. G10 remains the economical choice for general barriers away from the arc zone. The two convert the same way (waterjet, machining), so the step up is a material-line change, not a process change. [5] [11]

An arc barrier manages a fault event: plasma, pressure pulse, radiant flash, and the conductive residue arcs leave on surfaces. 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 flammability class (UL 94 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. Write the duty on the drawing so the right property set governs. [1]

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, mica chutes, laminate barriers, inorganic liners, 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. [1]

From this page's families: FR4 laminate (NP510A), Durostone UPM 203 and UPM S16, the ManniGlas grades (V-0 file classes), and the FST neoprene all report UL 94 V-0 on their TDS. Plain G10 is typically unclassed. Mica is inorganic and non-combustible rather than classed. RF-120 reports its own flammability data per its TDS. The class belongs to the specific grade as tested by the material manufacturer, so name the grade on the drawing and keep its TDS with the order file. H-O supplies the manufacturer's documentation with the converted part. [4]

Comparative tracking index, measured per IEC 60112, ranks how well an insulating surface resists forming carbonized conductive tracks under contamination and voltage. Switchgear compartments collect dust and condensation, and a tracked barrier conducts. Designs fail by tracking long before they fail by bulk puncture. Check the CTI line on the TDS for any barrier in a polluted or condensing compartment (the Durostone TDS reports it.

Laminate makers publish it per grade), prefer inorganic sheet where contamination is severe, and detail parts so creepage paths stay long. [5]

Muscovite FR / arc-rated grades are the standard for MV breaker arc chutes and general high-band barriers. Phlogopite is the maker-designated step above it, retaining its properties into the higher temperature bands (the HP-series designations in the phlogopite line), so specify it where the zone runs hotter than muscovite's class or where the maker's application guidance calls for it.

Both come as rigid plate (flat, structural, machinable) and flexible sheet (curved liners). The form choice follows the geometry, not the mineral. Specify mineral, form, and the maker's grade designation on the drawing.

Both are inorganic, but they solve different problems. ManniGlas is a non-woven glass paper: light, conformable, economical, die-cut into compartment liners, radiant shields, and fire-barrier layers, with UL 94 V-0 file classes and ASTM C177 thermal-conductivity data on the TDS. Mica is a built-up mineral sheet: stiffer, denser, non-carbonizing under arc exposure, and the right answer inside the chute and at the highest-band barrier points.

Practical rule: ManniGlas for fire-barrier lining duty, mica for arc-facing and highest-band duty, and a laminate behind either where the part carries load. [12]

If the part also has to conform, seal, or cushion, BISCO RF-120 heat-shield silicone foam: it carries compression data per ASTM D1056 with dielectric (D149) and dry-arc (D495) data on the TDS, so it can gasket and shield at once. If the exposure is continuous radiant heat with no sealing function, prefer the inorganic layer, ManniGlas or mica, which does not age the way organics do under radiation.

The two are often laminated: an inorganic face toward the heat with an elastomeric layer behind for conformity. H-O builds that as one converted part. [13]

Whenever the gear lives in an enclosed or occupied space, an electrical room, a basement substation, a walk-in lineup, where what a burning material emits matters as much as whether it burns. The data lines are ASTM E662 (specific optical density of smoke) and ASTM E162 (surface flammability under radiant heat), plus the maker's toxicity statements. On this page, the FST neoprene reports E662 with UL 94 V-0.

The kSil super-soft silicone sponge reports E162 / E662 on the sealing side. The inorganic families sidestep the question by not burning. NFPA 70E frames the workplace-safety context these rooms operate under. [8] [3]

H-O converts. We take laminate sheet, mica plate, glass paper, and elastomer stock from the material manufacturers and waterjet-cut, die-cut, machine, slit, and laminate it to your drawing. We do not press laminates or mold elastomers in-house. For barrier work that means: waterjet-cut G10 / Durostone plates with finished edges, die-cut mica chute plates to the breaker geometry, ManniGlas liners kiss-cut on adhesive, and laminated stack-ups (inorganic face plus elastomeric backer) as one part.

Material traceability and lot-code TDS records ship with production. If your assembly needs a molded component alongside, we coordinate through a partner network.

The drawing (DXF, STEP, or PDF) or a sample part, plus the duty context: arc-side or fire-side role, structural or lining function, continuous vs fault-event exposure, any UL 94 class or CTI requirement from the program spec, and whether FST data is needed for an enclosed room. Every part is made to order. Sample and production lead times are listed in the process strip above and confirmed with your quote through the form below.

Tolerance depends on the material class, the thickness, and the cut method. Soft foams and sponges move more than rigid laminates or films, so the achievable band is material-specific. Flag the critical dimensions on your drawing. Engineering confirms the achievable tolerance band for your geometry at drawing review, before tooling is committed. That review, not a generic chart, is what goes into the quote.

Yes. Send the sample part and engineering measures it, confirms the geometry back to you at drawing review, and quotes from that confirmed geometry. A drawing is still the fastest path, because nothing has to be reverse-measured. A DXF, STEP, or PDF with the material call-out shortens the review.