Custom Electrical Insulation & Dielectric BarriersNomex®, Kapton®, G10/FR4, Mica & Arc-Flash Protection

Clearance is the shortest distance between two conductors measured straight through the air. Creepage is the shortest distance between the same two conductors measured along the surface of the insulation between them. They fail differently: air breaks down in a single event and recovers, while a surface degrades cumulatively — dust, moisture and contamination slowly build a conductive track that ends in flashover.

Because surfaces track at distances where air would still hold, the required creepage is almost always longer than the required clearance, and IEC 60664 sizes the two separately, by working voltage, pollution degree and the material group of the insulation. In practice that means the barrier geometry, not just the barrier material, is doing the insulating: ribs, slots and extended skirts exist to stretch the surface path without moving the conductors. Send the working voltage and the environment, and the distances can be checked against the geometry before the part is cut.

Dielectric strength is the electric field a material withstands before it punctures, quoted in kV/mm (or V/mil) and measured per ASTM D149. It is the headline number on every insulation data sheet, and the most commonly misused one, because it is not constant with thickness: the kV/mm value falls as the gauge rises, so doubling the thickness does not double the withstand.

That is why a barrier is specified at its actual gauge, from the TDS row for that gauge, with margin for temperature, moisture and ageing — never scaled linearly from a one-mil test value. Thin films like polyimide carry remarkably high strength in a few mils, which is what makes a busbar wrap possible at all; thicker papers and laminates deliver their withstand alongside mechanical toughness. Send the withstand requirement and the space available, and the family and gauge can be matched, then confirmed on the data sheet.

Start with temperature, then space, then handling. Aramid paper (Nomex®) is the forgiving default for winding and barrier work: inherently flame-resistant, thermally stable to its 220 °C class, and tough enough to fold, form and survive assembly. Polyimide film (Kapton® / Apical®) delivers the highest dielectric strength per mil, so it wins where the insulation must live in a few thousandths — busbar wraps, slot liners in tight machines, layer insulation in power electronics.

PEEK film sits between them: a strong, chemical-resistant dielectric that takes mechanical abuse a thinner film cannot, at the cost of a lower temperature class than polyimide. The three are often combined — a laminate of paper and film gets the toughness of aramid and the strength of polyimide in one part. Send the temperature class, the withstand and the space, and the direction follows quickly.

UL 94 is the standard flammability test for polymeric materials used in devices and appliances, and V-0 is its strictest common vertical-burn class: the specimen self-extinguishes quickly without flaming drips. Inside switchgear, panelboards, battery packs and telecom power plants, insulation commonly must carry a V-0 rating so that an electrical fault does not become a fire.

Two cautions. First, the class belongs to a specific grade at a specific thickness, not to a material family — a family can hold V-0 and unrated grades side by side, so the rating is confirmed on the source TDS for the grade and gauge being cut. Second, V-0 is a flammability class, not an arc rating; arc-flash survival is a separate, assembly-level question. State the flame requirement on the spec and the grade is selected to carry it.

Use a rigid laminate when the part has a mechanical job as well as an electrical one. G10/FR4 glass-epoxy and Durostone® composite hold voltage while carrying load: busbar supports and braces, standoffs, phase barriers that must stay flat under fault forces, slot wedges, and structural isolation plates. A film or paper insulates, but it cannot brace anything.

The trade is formability and space. Films and papers fold, wrap and conform to geometry in a few mils; laminates arrive as flat, machinable sheet and take fasteners, slots and machined edges. Fault forces are the deciding load case for switchgear barriers — a barrier that deflects into a conductor during a fault was never a barrier. If the part must resist bending or impact, start with the laminate; if it must wrap or fold, start with the film or paper; and use both where the assembly needs both.

An arc-flash barrier is built for a transient, violent event rather than steady-state insulation: a fault arc releases a pressure wave, plasma, molten metal and hot gas in milliseconds, and the barrier has to keep that event away from people and adjacent compartments while the protection clears it. The materials are chosen for high-temperature survival and flame class first — glass-epoxy laminates, mica sheet, glass-fiber paper and other flame-rated barrier stock, alone or as laminated builds.

Geometry matters as much as material: coverage without gaps, supported spans that will not deflect into live parts, and edges and fastener holes cut cleanly so installation does not create the weak point. The incident energy the barrier faces is a system property, quantified per IEEE 1584 from the fault current and the clearing time. The barrier is specified against that system requirement — send the equipment class and the zone geometry, and the build follows.

Reach for mica when the barrier must insulate at a temperature that would destroy an organic material. Mica is an inorganic mineral with excellent dielectric strength that it keeps at several hundred degrees, which is why it is the classic barrier around heater elements, in furnace-adjacent equipment, between busbars and frames in hot zones, and in arc-facing positions where a polymer would char, melt or lose its withstand. Glass-fiber paper plays the same inorganic role as a thin insulation and fire-protection ply.

Below those temperatures, mica usually loses to the alternatives: it is fragile, it does not take mechanical load the way a laminate does, and it does not fold the way a film does. So the rule is simple — ordinary temperatures favor films, papers and laminates chosen by geometry and load; extreme temperature with an electrical-isolation requirement favors mica or glass paper. Confirm the grade temperature rating and dielectric strength on the data sheet, and send the slot and hole detail, because clean converting is what keeps a fragile sheet usable.

Insulation ages thermally. Every material has a temperature class — the classic letter classes (105 A, 130 B, 155 F, 180 H, 220 °C for aramid systems) — that reflects how long it keeps its dielectric and mechanical properties at temperature. Run a material above its class and it does not fail immediately; it fails early, embrittling and losing withstand over months and years. That slow trade is invisible at commissioning and decisive over the equipment life.

This is why winding insulation is specified by class before anything else: the hottest spot in the machine, not the ambient, sets the requirement. It is also why the high classes are dominated by aramid paper, polyimide film and the inorganics. State the continuous operating temperature and the hot-spot allowance, and the family follows almost automatically — then the specific grade is confirmed against the manufacturer’s thermal-endurance data.

More gauge does add withstand, but not proportionally, and sometimes not usefully. Dielectric strength in kV/mm falls as thickness rises, so each added mil buys less than the one before it. Past the point where the puncture requirement is met with margin, extra thickness mostly buys cost, weight and assembly problems — and it does nothing at all for the failure mode that actually governs many designs, which is tracking along the surface.

If the creepage distance is short, a thicker barrier is no better than a thin one; the fix is geometry — a longer surface path, ribs, or a skirt — or a material with better tracking resistance, not more gauge. The clean method is: size creepage and clearance first per IEC 60664, then pick the thinnest gauge that meets the puncture withstand with margin at temperature on the TDS. Send both requirements and the part gets sized in that order.

Not in the way a material is certified to UL 94, and the distinction matters on a spec. IEC 60664 and IEEE 1584 are system-level standards: 60664 tells the equipment designer how much creepage and clearance the assembly needs; 1584 tells the facility engineer how much incident energy a fault would deliver. A sheet of laminate cannot hold either certification — what it holds are material properties that feed those calculations, like its comparative tracking index, dielectric strength, temperature class and flame class.

So the honest spec language is that a material supports compliance: its CTI places it in a material group that shortens the required creepage under 60664, its flame and temperature ratings qualify it for a barrier position sized under 1584. H-O quotes materials with the TDS values that feed your calculation, and does not claim system certifications on a material’s behalf. Send the standard you are designing to and the values you need, and the data sheet gets checked against them.

Send the job first: dielectric barrier, creepage control, arc-flash protection, structural isolation, winding insulation, or several at once. Then the electrical numbers — system voltage and the withstand requirement, and the creepage and clearance distances if the geometry already fixes them. Then the environment: continuous and peak temperature, moisture, oil or chemical exposure, and any flame-class requirement. Then the part itself: geometry or a drawing, the gauge or space available, adhesive and liner needs, and the prototype and annual volume.

With that set, engineering can match a family, a grade direction and a converting approach, then confirm the grade-level values against the manufacturer’s data sheet. The “What to send H-O” box below lists these. If you only have the symptom — “this barrier tracked,” “this gear needs arc baffles,” “this pack fails hipot” — that is a fine starting point; describe it and we will work back to the numbers.

H-O is a precision converter, not a raw-material producer. We do not make the aramid paper, film, laminate, mica or sponge stock; we buy sheet, roll and board stock from the material manufacturers and convert it to your drawing, by die-cutting, kiss-cutting, laser and waterjet cutting, machining, adhesive lamination, slitting and kitting, with material traceability and lot-level data-sheet records.

Every insulation part is made-to-order; we do not carry finished parts in stock and we do not advertise a no-minimum policy, though prototype quantities through full production runs are equally welcome and the minimum varies by material and part. Samples run typically 3–5 business days for common configurations, standard production about two weeks. Send your drawing or describe the insulation system through the form below for a specific quote.