Phenolic Glass Melamine Sheet

NEMA G9 melamine-glass laminate sheet is the arc-barrier specialist among glass-reinforced laminate flat stocks — combining 180–240+ second arc resistance, very low water absorption (0.1–0.5%), and 155°C (311°F) Class F continuous service in panels suitable for high-voltage switchgear arc barriers, outdoor electrical enclosure panels, and Class F motor insulation barriers at lower cost than G7 silicone-glass.

TL;DR — NEMA G9 Sheet Quick Facts

Standard Sizes — NEMA G9 Sheet

Per NEMA LI 1:

Standard thickness increments: 1/16, 1/8, 3/16, 1/4, 3/8, 1/2, 5/8, 3/4, 1, 1¼, 1½, 2 inches.

G9 sheet availability is broader than G7 but narrower than G5 or G10 — confirm availability for non-standard thicknesses at quotation.

Properties Relevant to Sheet Form

G9 melamine-glass sheet excels in arc resistance and moisture stability while providing mechanical strength competitive with G7:

Where G9 beats G7 in flat-stock applications:

• Higher room-temperature flexural and compressive strength (stiffer panel per unit thickness)
• Equal or better arc resistance in many test conditions
• Lower cost per panel than G7 for the same size and thickness

Where G7 is preferred over G9:

• When 180°C Class H thermal rating is required (G9 is Class F only)
• When the installed environment exceeds 155°C sustained

For most switchgear arc barrier and Class F insulation applications, G9 is the better value versus G7.

For the full datasheet, see Phenolic Glass Melamine properties.

Typical Applications — Sheet Form

G9 sheet applications concentrate on arc resistance and moisture stability in outdoor and industrial electrical installations:

Switchgear arc phase barriers and arc chutes — G9 sheet cut into phase barrier panels and arc chute sidewalls in medium-voltage (4.16–34.5 kV) metal-enclosed switchgear. The 240+ second arc resistance means the panel withstands multiple fault-clearing events without carbonizing through — critical for phase-barrier integrity that, if lost, can escalate a single-phase fault to a three-phase bus fault.

Outdoor electrical enclosure insulating panels — G9 sheet's very low water absorption (0.1–0.5% at 24 hours) makes it the preferred panel material for outdoor-rated electrical equipment: junction boxes, metering enclosures, transformer terminal boxes, and substation equipment installed in rain-exposed locations where paper or fabric phenolic would absorb moisture and lose dielectric strength.

Class F motor stator insulation panels — IEC 60034 Class F insulation systems (155°C rated) in medium and large AC motors require inter-phase barriers and coil cover sheets rated to Class F. G9 sheet at 155°C continuous satisfies this requirement at lower cost than G7 (180°C) while meeting the actual thermal class requirement.

Bushing and terminal board panels in medium-voltage equipment — G9 sheet machined into terminal boards and bushing mounting panels in pad-mounted transformers and network protectors where the combination of medium voltage (4.16–15 kV), outdoor installation, and arcing exposure at the terminal makes G9's properties mandatory.

Industrial power distribution arc isolation panels — Horizontal bus compartment arc barriers and arc path deflectors in 480 V and 4.16 kV switchboards, motor control centers, and panelboards where short-circuit fault energy can cause sustained arcing at the bus and the barrier must contain the arc.

High-humidity electrical apparatus insulating panels — Chemical plant, coastal industrial, and tropical-service electrical equipment where panel board moisture absorption from the environment over years of service would compromise a standard phenolic grade. G9's melamine resin resists moisture uptake far better than paper or fabric phenolic.

Machining Notes — Sheet

G9 sheet machines similarly to G5 glass-phenolic with the same requirement for carbide or PCD tooling:

Sawing: Carbide-tipped blade (60–80 tooth); diamond blade for production volume. G9 melamine-glass can be slightly harder to saw than G5 due to the stiffer melamine resin matrix — maintain blade sharpness and use consistent feed rate.

Routing and milling: Solid-carbide spiral bit; climb milling preferred at final pass. G9 sheet edges are cleaner than G7 silicone-glass due to the better resin-to-fiber adhesion of melamine — expect lower edge fiber fraying.

Drilling: Solid-carbide drill, 400–600 SFM. Backer board required at exit face. G9 drills with excellent hole wall quality — the hard melamine resin matrix supports the glass fiber during drilling and minimizes pull-out.

Punching: G9 sheet at 1/16"–3/16" thickness can be punched at room temperature using sharp steel dies — the melamine resin formulation (without a specific "P" punching modifier) allows modest punching if dies are sharp and clearance is correct. For production punching, confirm with the supplier whether a specific punching-grade G9 is available.

Laser cutting: G9 melamine-glass sheet can be laser-cut; melamine combustion products are toxic — thorough exhaust ventilation and laser fume extraction are mandatory. Laser cutting produces a clean edge in G9 due to the resin's char behavior.

Dust control: HEPA exhaust ventilation; NIOSH P100 respirator; closed machining area. Melamine decomposition products and glass fiber are both respiratory concerns.

See Phenolic Glass Melamine Machining Guide.

Standards and Compliance

Request a Certificate of Conformance citing NEMA LI 1 Grade G9 on every order. For Class F motor insulation qualification, request the thermal classification documentation.

More related guides

Applications

• Electrical Insulation — Phenolic & Laminate Options
• Aerospace Interior Plastics

Industries

• Electrical Power & Distribution
• Defense & Military Plastics
• General Industrial Plastics

Compare materials

• G7 vs. G9 Laminate Comparison
• Phenolic Paper vs. Glass Phenolic

Other NEMA G9 forms

• Phenolic Glass Melamine Rod
• Phenolic Glass Melamine Tube