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G10, Durostone, Mica, Nomex, or PEEK: Choosing Busbar, Transformer, and Motor Insulation
Busbar, transformer, and motor insulation arrives in three mechanical forms, and the form decides the family before the brand does. Structural parts (supports, plates, wedges) want laminate stiffness; formed parts (slot liners, layer insulation, wraps) want paper toughness; space-critical layers want film at tens of microns.
This guide walks the ten families the H-O busbar, transformer, and motor insulation application page covers, with the governing frameworks named by designation: NEMA LI 1 for the laminate grade system, IEC 60664-1 for creepage and clearance, IEC 60112 for tracking, IEC 60243 for electric strength, IEC 60085 and UL 1446 for thermal class and insulation systems, and UL 94 for flammability classes.
Per-grade values quoted are the maker-TDS and dossier figures cited on the parent page.
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The families, by the decision each one wins
Glass-epoxy laminate: the structural default
Glass-epoxy laminate holds busbar on centers, takes the magnetic forces of a fault, and keeps its dielectric properties while doing it.
The Norplex line maps directly to the NEMA LI 1 grade system: NP510 (G10) for general supports, NP511 (FR4) where a flammability listing is required (the dossier flags UL 94 V-0 for this family), and NP512 (G11) where strength retention at elevated temperature matters, in 1/32 through 1/4 inch sheet per the dossier.
H-O waterjet-cuts and machines these laminates with clean, delamination-free edges; sawing and routing left to chance produce fiber pull-out and micro-cracks that become moisture paths in a part that exists to take fault forces.
Durostone composite: when tracking or arc exposure drives the spec
Durostone composite is the step up when the environment is dusty, damp, or arc-exposed. Its TDS carries comparative tracking data per IEC 60112, electric strength per IEC 60243 (the EPC 203 grade reports 16 kV/mm), thermal-endurance methods per IEC 60216, and UL 94 V-0 listings on the UPM grades (UPM 203, UPM S16), the qualification package for arc-chute parts and tracking-critical isolation plates. Standard G10 and FR4 stay the economical answer for clean, sheltered positions.
Mica: the inorganic, non-carbonizing barrier
Muscovite mica is the established choice for MV phase barriers, arc chutes, and HV winding insulation because its inorganic surface does not form carbon tracks, in rigid FR plate, flexible sheet, tape, and paper forms per the dossier. Phlogopite mica extends the range into extreme-temperature zones; the HP5J class is rated toward 1000 °C per the maker literature. Thin rigid mica is brittle: specify it laminated to a backing where assembly handling is rough, and H-O converts the lamination as one part.
Aramid paper: the 220 °C class system backbone
Nomex aramid paper is the backbone of 220 °C class insulation systems under the IEC 60085 framing, with system qualification under UL 1446.
The dossier maps the grade range by role: 410 the standard grade for layer insulation, slot liners, and wraps (1 to 10 mil); 414 the high-density grade where stiffness and the heavier hand help (2 to 7.5 mil); 411 in its own niche; 464 the meta/para blend; and 818 the high-temperature pressboard for structural insulation. Aramid folds, creases, and survives insertion against lamination edges, which is why it owns the slot. For the calendered-versus-uncalendered decision in detail, see NOMEX 410 vs. 411: choosing aramid paper for motor and transformer insulation.
Polyimide and PEEK films: the thin, hard-working layers
Polyimide film (Kapton HN in 50 through 500 gauge classes, heat-sealable Kapton FN, Apical NP in 25 to 125 micron, per the dossier and maker literature) carries phase insulation and ground layers at minimum thickness, with dielectric strength per ASTM D149 on the maker TDS.
When the design brief is more power in less space, APTIV PEEK film steps up: the standard series (50 micron class per TDS) reports dielectric methods per ASTM D149/D150/D257 with tensile modulus classes from 2300 to 4500 MPa, and the XPI high-performance series adds IEC 60112, IEC 60243, IEC 60250, and IEC 60270 partial-discharge methods plus UL 746B long-term evaluation on its TDS, the data set demanding insulation engineers actually ask for.
Glass-fiber paper and solid silicone: the supporting cast
ManniGlas glass-fiber paper (1200, 1900, 1902, 2000) backs windings as the fire and thermal barrier: inorganic, with UL 94 listings and ASTM C177 thermal data per TDS. It is the back-stop, not the primary dielectric. BISCO solid silicone supplies the compliant dielectric pads and interface sheets in coil and HV assemblies, with tight-tolerance specialty grades where the stack is toleranced hard.
Insulation Families Side by Side
| Family | Mechanical form | Tracking / arc behavior | Temperature position | Typical role |
|---|---|---|---|---|
| Glass-epoxy G10 / FR4 / G11 | Structural laminate | Verify CTI group per grade TDS | G11 for elevated duty | Busbar supports, plates, general barriers |
| Durostone composite | Structural laminate | IEC 60112 data on TDS | Per maker designations | Arc-chute parts, tracking-critical plates |
| Muscovite mica / phlogopite | Rigid plate or flexible sheet | Inorganic, non-carbonizing | Phlogopite toward 1000 °C class | MV phase barriers, arc chutes, HV windings |
| Nomex aramid paper | Folds, creases, survives insertion | Per grade TDS | 220 °C class systems | Slot liners, layer insulation, wraps |
| Polyimide film | Thin film; wants support at folds | Per grade TDS | High-temperature thin-film standard | Phase and ground layers at minimum gauge |
| APTIV PEEK film (XPI) | Film with mechanical duty | IEC 60112 / 60243 / 60270 on TDS | Compact high-power designs | The most demanding thin barriers |
| ManniGlas glass-fiber paper | Paper | Inorganic | Fire / thermal back-stop | Behind windings and hot faces |
Illustrative and relative only; confirm each grade on its current technical data sheet. Required creepage and clearance come from the IEC 60664-1 tables applied to your design; CTI groups differ between grades of the same family.
Pick the mechanical form before the brand
A laminate where a paper belongs cracks at the fold; a paper where a laminate belongs buckles under fault force; and a film asked to do either needs a laminated construction. Where slot fill is the binding constraint, the converted answer is often both: a paper-film-paper lamination that H-O supplies as a single die-cut, creased part, pairing the film's dielectric strength with the paper's forming toughness. Specify crease orientation and burr-free edges on the drawing; a crack-free crease on a liner is a conversion specification, not luck.
How H-O Products helps
H-O Products converts; we do not press laminate or make paper in-house. We take laminate sheet, mica plate, paper, and film from the material manufacturers and waterjet-cut, die-cut, CNC knife-cut, slit, and laminate them to your drawing: clean laminate edges with no heat-affected zone, creased and formed slot liners cut to the machine's slot map, mica bonded to backings, and material traceability with lot-code TDS records under our ISO 9001:2015 certified quality management system in Winsted, Connecticut.
Rewind shops are repeat buyers here: the same liners, wedges, and separators, held on the die or CNC program for repeat orders.
Frequently asked questions
G10 vs FR4 vs G11: which laminate do I specify?
All three are NEMA LI 1 glass-epoxy grades and the Norplex line maps to them directly: NP510 (G10) is the general-purpose structural insulator; NP511 (FR4) adds the flammability listing (the dossier flags UL 94 V-0 for this family) and is the default where a listing is required; NP512 (G11) retains strength at elevated temperature. The dossier covers 1/32 through 1/4 inch sheet; verify per-grade values on the maker TDS.
When does Durostone composite replace standard glass-epoxy?
When tracking or arc exposure drives the spec. Durostone's TDS carries comparative tracking data per IEC 60112, electric strength per IEC 60243 (EPC 203 reports 16 kV/mm), thermal-endurance methods per IEC 60216, and UL 94 V-0 listings on the UPM grades, the qualification package for arc-chute parts and tracking-critical isolation plates in dusty or damp gear. Standard G10 and FR4 stay the economical answer for clean, sheltered positions.
Nomex paper or Kapton film for slot liners?
Mechanically different answers to the same electrical question. Aramid paper folds, creases, and survives insertion against lamination edges, which is why it is the slot-liner standard; polyimide film carries more dielectric strength per mil but wants support at folds. Where slot fill is the binding constraint, the converted answer is often a paper-film-paper lamination supplied as a single die-cut, creased part. Frame slot geometry and crease orientation on the drawing.
When is PEEK film worth specifying over polyimide?
When the design is compact and high-power and the film must carry mechanical as well as dielectric duty, or when the qualification package is the requirement. APTIV standard grades report dielectric methods per ASTM D149/D150/D257 with tensile modulus classes from 2300 to 4500 MPa per TDS, and the XPI series adds IEC 60243 electric strength, IEC 60270 partial-discharge methods, IEC 60112 CTI, and UL 746B long-term evaluation. For general wraps and barriers, polyimide remains the economical thin-film standard.
Get a busbar and winding insulation recommendation
Tell us the job (support, barrier, liner, or wrap), the working voltage and spacing, the thermal class, and any arc exposure, 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
- NEMA LI 1 (industrial laminates: the G-10 / FR-4 / G-11 grade system); IEC 60664-1 (insulation coordination: creepage and clearance).
- IEC 60112 (comparative tracking index); IEC 60243 and ASTM D149 (electric strength); IEC 60085 (thermal classes); UL 1446 (insulation systems); UL 94 (flammability, per grade); UL 746B (long-term evaluation, cited on the APTIV XPI TDS).
- IEEE C37.20 and IEC 61439 (the switchgear assembly standards these parts live inside).
- Manufacturer technical data sheets and dossier entries: Norplex glass-epoxy, Durostone composite, muscovite and phlogopite mica, Nomex aramid paper, Kapton and Apical polyimide, APTIV PEEK, ManniGlas, BISCO solid silicone.
This article summarizes insulation material-selection principles for busbar, transformer, and motor work using the families and published methods cited on the parent application page. Comparisons are qualitative; per-grade values quoted are maker-TDS and dossier figures and must be confirmed on the manufacturer's current technical data sheet. Required creepage and clearance come from the IEC 60664-1 tables applied to your design, and insulation-system qualification under UL 1446 belongs to the equipment program.
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 independently certify materials or finished assemblies.