NEMA G9 Grades: Phenolic Glass Melamine Laminate

NEMA LI 1 defines G9 as the glass-cloth-reinforced laminate bonded with melamine resin, distinguished from other NEMA glass grades primarily by its outstanding arc resistance (>180 seconds) and track resistance (CTI ≥600). There is one primary commercial grade designation — NEMA G9 — supplemented by the military specification MIL-I-24768/2 Type GME for defense procurement. This page explains what the grade designations mean, how G9 compares to related grades, and how to specify the right grade for your application.

At a Glance

• Only one commercial grade: NEMA LI 1 Grade G9 — melamine resin, woven glass cloth
• Military equivalent: MIL-I-24768/2 Type GME
• No FR-rated sub-grade (unlike G10 and FR4 distinction within epoxy glass)
• Primary differentiator from other NEMA grades: resin type — melamine vs. epoxy (G10 and FR4) vs. silicone (G7) vs. phenolic (G-3)
• Key grade-selection factors: arc resistance requirement, operating temperature, mechanical load, cost

NEMA LI 1 Grade G9: Definition and Minimum Requirements

NEMA LI 1 (Industrial Laminated Thermosetting Products) is the governing standard for all commercial thermoset laminates in the United States. Grade G9 is defined by both its composition (woven glass cloth + melamine resin) and its minimum performance thresholds:

The NEMA standard sets minimums; most commercial G9 exceeds these values, particularly arc resistance (which is already at the top of the D495 scale) and dielectric strength (often 420–450 V/mil in practice).

MIL-I-24768/2 Type GME: Military Grade G9

MIL-I-24768/2 is the military specification for glass-melamine laminate, designated Type GME. It closely parallels NEMA G9 in composition and performance requirements but adds:

• Tighter dimensional tolerances on sheet thickness and flatness
• Lot-specific testing requirements: arc resistance, dielectric strength, and flexural strength must be tested per lot, with test reports provided
• Traceability: material must be traceable to a qualified manufacturer list
• Specific conditioning procedures before electrical testing (48 hr at 50°C per MIL-STD-202)

MIL-I-24768/2 procurement is required for Navy, Army, and Air Force switchgear applications. When quoting G9 for military end-use, specify "MIL-I-24768/2 Type GME certified" and confirm the supplier maintains qualification.

How G9 Fits in the NEMA Glass Laminate Family

The NEMA glass laminate grades differ primarily in resin, not reinforcement (all use woven E-glass cloth). The grade selection determines the temperature rating and the electrical surface behavior:

Key observations:

• G9 vs. G10 and FR4: G9 has 3–4× higher arc resistance and substantially higher CTI. G10 and FR4 has superior tensile strength and lower cost. Select G9 when arc or track resistance governs.
• G9 vs. G7: Both achieve >180 sec arc resistance and CTI ≥600. G7 adds 50°F+ of continuous use temperature via its silicone resin but at significantly higher material cost. If max temperature is ≤350°F, G9 is the cost-effective choice.
• G9 vs. G-3: G9 outperforms G-3 in arc resistance, CTI, and moisture absorption. G-3 is lower cost but is not appropriate for arc-chute or high-track-resistance applications.

Grade Selection Decision Tree

Use this logic to confirm G9 is the right grade:

1. Is arc resistance or track resistance the primary electrical concern?

   • Yes → proceed to step 2
   • No → consider G10 and FR4 for general insulation, G-3 for low-cost general use

2. Is the continuous operating temperature ≤350°F?

   • Yes → G9 is appropriate
   • No → specify G7 (phenolic glass silicone) for temperatures up to 400°F+

3. Is this a military or defense procurement?

   • Yes → specify MIL-I-24768/2 Type GME with lot certification
   • No → NEMA LI 1 Grade G9 is sufficient for commercial switchgear

4. Does the design require high tensile or impact strength?

   • High impact required → reconsider G10 and FR4 (tensile ~40,000 psi vs. G9's ~20,000 psi); G9 if arc resistance still governs
   • Standard switchgear structural loads → G9 is adequate

Flame and Flammability Rating

G9 does not carry a UL 94 V-0 or HB rating as a standard designation; NEMA G9 is defined by NEMA LI 1 test methods, not UL 94. However, G9 is inherently self-extinguishing due to the glass cloth reinforcement and melamine resin chemistry. Where a UL 94 V-0 rating is contractually required, confirm with the specific supplier whether their G9 product has been UL 94 evaluated.

G10 and FR4 carries a UL 94 V-0 rating as part of its "FR" (flame retardant) designation. If a UL 94 V-0 certification on the material itself is required and G9 properties are acceptable, confirm the rating with your supplier before committing to the spec.

Procurement Notes

Standard commercial G9: Order by NEMA LI 1 Grade G9, form (sheet/rod/tube), nominal dimensions, and quantity. Material is manufactured by major laminate producers and is a stock item at specialty plastics distributors.

Military G9 (MIL-I-24768/2 Type GME): Requires a qualified manufacturer (check the QPL). Lead times are typically 4–12 weeks for certified lots. Request a Certificate of Conformance and lot-specific test report with your order.

Custom thicknesses: Standard sheet thicknesses run 0.031 in through 4.000 in. Non-standard thicknesses may require minimum order quantities and 6–12 week lead times.

For full sizes and availability, see the G9 specifications page.

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