NEMA Grade Selection Guide — Which Thermoset Laminate Do You Need?

NEMA grades define thermoset laminate types by reinforcement, resin system, and performance properties — selecting the wrong grade wastes cost margin or causes premature field failure, so this guide maps each grade to its intended application.

TL;DR — Key Takeaways

• NEMA grades are defined in NEMA LI-1 and mirrored (with minor differences) in ASTM D709
• The grade designation tells you the reinforcement (X = paper, C = cotton, G = glass) and resin (phenolic, epoxy, melamine, silicone)
• G10 and FR4 are both glass-epoxy but are different materials: G10 is UL 94 HB; FR4 is UL 94 V-0 (brominated flame retardant)
• For electrical insulation in switchgear, bus bars, and transformers, start with G10 or FR4 unless cost drives you to phenolic
• For structural mechanical parts with incidental electrical service, cotton-phenolic (CE/LE) is usually the right cost/performance balance

How NEMA Grades Are Structured

NEMA LI-1 (Industrial Laminated Thermosetting Products) groups grades by:

1. Reinforcement type: Paper (X), Cotton fabric (C), Linen fabric (L), Glass fabric (G), or Glass mat (GPO)
2. Resin system: Phenolic (most grades), Epoxy (G10/G11/FR4/FR5), Melamine (G5/G9), Silicone (G7), Polyester (GPO)
3. Special requirements: Flame retardancy (FR prefix), low-loss electrical (XXX), punchability (P suffix), high-temp (G11 vs G10)

The grade letter codes do not spell out these components directly — the table below decodes them.

Complete NEMA Grade Reference

Selection Logic by Application

High-Voltage Electrical Insulation

For standoffs, barriers, support structures, and spacers in equipment rated above 600V:

Best choice: G10 or FR4

• If UL 94 V-0 is required by code or specification → FR4
• If flame retardancy is not required → G10 (slightly lower cost, equivalent electrical performance)
• If continuous service temperature exceeds 130°C → G11 (G10) or FR5 (FR4 equivalent)

Do not use paper-phenolic (XX/XXX) for sustained HV duty where humidity can be present — moisture absorption drops dielectric strength by 35–45%.

Switchgear Arc Barriers and Arc Chutes

Best choice: GPO-3 or G5/G9

• GPO-3 is the industry standard for arc barriers in modern switchgear — UL 94 V-0, good arc resistance, cost-effective
• G5/G9 provides higher arc resistance for severe-duty arc chutes in circuit breakers
• See the Arc Chute Materials guide for detailed arc-quench performance data

PCB Substrates

Best choice: FR4 (nearly universal for standard PCBs)

• FR4 is the global default PCB substrate — UL 94 V-0, controlled Dk/Df, wide laminator availability
• G10 is not a drop-in substitute for FR4 in PCB applications — G10 lacks the required flame retardancy for IPC Class 1 boards
• High-temperature PCBs (power electronics, under-hood automotive) may require FR5 or specialty polyimide substrates

Mechanical Parts with Incidental Electrical Service

Gears, bushings, spacers, and structural brackets that see voltage but are primarily structural:

Best choice: Cotton-phenolic (CE or LE)

• Lower cost than G10 and FR4
• Excellent machinability — machines more like a metal than glass-epoxy
• Adequate electrical performance for < 600V dry service
• For wet or outdoor service, step up to G10

Cost-Sensitive Indoor Electrical Panels (Low Voltage)

Best choice: XX or XXX phenolic

• Lowest material cost in the thermoset family
• Adequate for 600V-and-below dry indoor service
• Excellent cold-punchability (XXXP) for high-volume punched terminal boards
• Not recommended where moisture, chemicals, or elevated temperature are factors

NEMA Grade Cross-Reference to Military Grades (MIL-I-24768)

See the full MIL-I-24768 Explained guide for complete military designation decoding.

Quick-Select Decision Table

More related guides

Applications

• Switchgear Insulation Materials
• Arc Chute Materials
• Transformer Insulation Materials
• Terminal Board Materials

Materials

• G10 Material Hub
• FR4 Material Hub
• Canvas-Phenolic Material Hub
• Linen-Phenolic Material Hub