Views: 0 Author: Site Editor Publish Time: 2026-08-17 Origin: Site
Electrical insulation components must perform reliably under voltage, heat, moisture, mechanical load and, in some applications, electrical arcing. Choosing a material based only on mechanical strength or price may result in electrical tracking, dimensional instability, premature aging or failure to meet the applicable standard.
Sheet Molding Compound (SMC) is a ready‑to‑mold thermoset composite commonly made from unsaturated polyester or vinyl ester resin, chopped glass fiber, mineral fillers and functional additives. It is generally processed by compression molding and can combine electrical insulation, mechanical strength, corrosion resistance, dimensional stability and efficient high‑volume production.
These characteristics make electrical‑grade Sheet Molding Compound suitable for meter boxes, electrical enclosures, switchgear components, busbar supports, insulating barriers, terminal boards, circuit‑breaker housings and other electrical parts.
However, not every SMC grade provides the same electrical performance. The correct material must be selected according to the operating voltage, installation environment, fire requirements, mechanical load, component geometry and molding process.
This guide explains the main properties that buyers and engineers should evaluate when choosing Sheet Molding Compound for electrical insulation applications.
Table of Contents
Electrical‑grade Sheet Molding Compound is an SMC formulation designed to provide controlled electrical insulation and, when required, flame‑retardant performance.
A typical electrical‑grade SMC formulation contains:
Thermosetting polyester or vinyl ester resin
Chopped glass fiber reinforcement
Mineral fillers
Thickening agents
Low‑shrink or low‑profile additives
Flame‑retardant additives
Pigments
Internal release and processing additives
The resin system affects chemical resistance, thermal behavior, water absorption and electrical insulation. Glass fiber provides strength, stiffness and dimensional stability. Fillers and additives are used to adjust flame retardancy, material flow, shrinkage, surface quality, color and cost.
Because these ingredients interact with each other, simply increasing the glass fiber or flame‑retardant content does not necessarily produce a better material. A successful electrical‑grade Sheet Molding Compound must balance electrical, mechanical, thermal and processing properties.
JLON supplies SMC materials for electrical, industrial and structural applications. In addition to standard grades, the formulation can be adjusted according to the customer’s component, molding conditions and required performance.
Sheet Molding Compound can be compression‑molded into complex parts incorporating ribs, bosses, mounting holes, metal inserts and integrated fastening features.
Common electrical insulation applications include:
Electrical meter boxes
Distribution boxes and cabinets
Electrical enclosures
Switchgear parts
Circuit‑breaker housings
Busbar supports
Insulating barriers
Terminal boards and terminal blocks
Transformer components
Cable distribution components
Outdoor utility enclosures
Railway electrical components
Industrial control equipment
Electrical equipment covers and bases
Different components require different combinations of properties.
An outdoor meter box may prioritize flame retardancy, weather resistance, impact strength and low water absorption. A busbar support may place greater emphasis on tracking resistance, dielectric strength, thermal resistance and dimensional stability. A circuit‑breaker housing may require arc resistance, heat resistance and reliable material flow around a complex mold cavity.
For this reason, the general description “electrical‑grade SMC” is not enough to identify the correct material.
Dielectric strength indicates how much electrical stress an insulating material can withstand before electrical breakdown occurs. It is commonly expressed in kilovolts per millimeter, or kV/mm.
A higher value generally indicates greater resistance to electrical breakdown. However, the reported result depends on several factors:
Test method
Specimen thickness
Electrode configuration
Voltage application rate
Material conditioning
Temperature and humidity
Voids or defects in the specimen
When comparing Sheet Molding Compound suppliers, buyers should not compare only the numerical dielectric‑strength values. The corresponding test standards and test conditions should also be reviewed.
JLON grade 5002(L), an electrical insulation and flame‑retardant Sheet Molding Compound, has a specified dielectric strength of at least 12 kV/mm.
This value provides useful material‑level information, but the final molded component should still be validated at its actual wall thickness and operating voltage. Fiber orientation, weld lines, metal inserts, molding defects and surface contamination can all affect the electrical performance of a finished part.
The Comparative Tracking Index (CTI) measures the resistance of a solid insulating material to electrical tracking across its surface under wet and contaminated test conditions.
Electrical tracking occurs when a conductive path gradually develops on the material surface. It can be caused by electrical stress combined with moisture, dust, salt or other contaminants. Once a carbonized conductive path forms, insulation performance may deteriorate rapidly.
CTI is expressed in volts. A higher CTI generally indicates stronger resistance to surface tracking.
Under the commonly used material‑group classification:
Material Group I: CTI of 600 V or higher
Material Group II: CTI from 400 V to below 600 V
Material Group IIIa: CTI from 175 V to below 400 V
Material Group IIIb: CTI from 100 V to below 175 V
The exact selection must follow the applicable component standard and insulation‑coordination requirements. CTI may influence the required creepage distance, but a high CTI value does not independently prove that the finished component is compliant.
JLON 5002(L) electrical‑grade SMC has a specified CTI of at least 600 V. This makes it a potential material for applications requiring high tracking resistance, subject to confirmation against the customer’s test method, product design and certification requirements.
CTI and PTI are related, but they should not be treated as identical properties.
CTI means Comparative Tracking Index. It is used to determine the material’s tracking‑resistance level by testing at different voltages.
PTI means Proof Tracking Index. It verifies whether a material can withstand a specified test voltage under defined conditions without tracking failure.
If a drawing or technical specification states “PTI 600,” it should not automatically be recorded as “CTI 600.” The buyer and SMC supplier should confirm:
Whether CTI or PTI is required
The applicable test standard
Required test voltage
Number of specimens
Conditioning requirements
Acceptance criteria
When requesting an electrical insulation SMC quotation from JLON, customers should provide the original drawing or standard whenever possible. This reduces the risk of selecting a grade based on an incorrectly interpreted abbreviation.
Arc resistance measures how long the surface of an insulating material can resist forming a conductive path when exposed to a high‑voltage, low‑current electrical arc. The result is commonly expressed in seconds.
This property may be important for:
Switchgear components
Circuit‑breaker housings
Terminal components
Insulating barriers
Components near switching contacts
Parts exposed to intermittent electrical arcing
JLON 5002(L) Sheet Molding Compound has a specified arc resistance of at least 180 seconds.
Arc resistance should not be confused with arc‑flash protection or the ability of a complete enclosure to contain a high‑energy electrical fault. Those are system‑level requirements involving the material, component design, wall thickness, assembly method, pressure release and applicable equipment standard.
The arc‑resistance value reported on an SMC technical data sheet describes the material under specified laboratory conditions. Finished‑component validation remains necessary.
Many electrical components require flame‑retardant SMC. However, the phrase “flame retardant” is incomplete unless it is supported by a specific test standard, classification and tested thickness.
Possible fire‑performance requirements include:
UL 94 classification
Limiting Oxygen Index
Glow‑wire testing
Ignition resistance
Flame‑spread requirements
Smoke and toxicity limits
Halogen‑free requirements
Industry‑specific fire standards
Before choosing flame‑retardant Sheet Molding Compound, confirm:
Which fire test standard applies?
What classification is required?
At what specimen thickness?
Is third‑party certification necessary?
Is a halogen‑free formulation required?
Are smoke and toxicity limits specified?
Does the required color affect the tested formulation?
JLON 5002(L) is designed as a flame‑retardant electrical insulation grade. The exact classification should be added from the corresponding test report before the information is published or included in a customer specification:
Flame‑retardant classification: [TO BE ADDED]
Test standard: [TO BE ADDED]
Tested thickness: [TO BE ADDED]
A flame rating should never be claimed solely based on the formulation. It should be supported by a valid test report covering the relevant grade and thickness.
Electrical equipment may experience continuous operating heat, temporary temperature peaks or localized temperature rise near conductors and electrical contacts.
Heat Deflection Temperature, commonly abbreviated as HDT, is one property frequently reported on an SMC technical data sheet. It indicates the temperature at which a specimen reaches a defined deformation under a specified mechanical load.
JLON 5002(L) has a specified HDT of at least 200°C.
However, HDT is not the same as the continuous operating temperature. Long‑term thermal suitability may require evaluation of:
Thermal aging
Temperature index
Mechanical‑property retention
Electrical‑property retention
Dimensional stability
Oxidation or discoloration
Duration of heat exposure
Mechanical load applied to the component
When an application has a specified continuous service temperature, customers should provide that information separately instead of selecting the SMC grade only according to its HDT.
Moisture can reduce surface resistance, influence dielectric performance and increase the risk of electrical tracking. Low water absorption is especially important for:
Outdoor electrical enclosures
Coastal environments
Humid industrial facilities
Underground electrical systems
Marine equipment
Components exposed to condensation
Equipment requiring a long service life
When comparing water‑absorption data, buyers should confirm the test method, immersion time, water temperature, specimen thickness and result unit.
JLON 5002(L) is described as having low water absorption. The numerical value and test method should be added to the technical table when confirmed:
Water absorption: [TO BE ADDED]
Test method: [TO BE ADDED]
For outdoor components, water absorption should be considered together with UV resistance, weathering, sealing design, corrosion resistance and temperature cycling.
Although the primary function may be electrical insulation, many molded SMC parts also carry mechanical loads.
Important mechanical properties may include:
Flexural strength
Flexural modulus
Tensile strength
Impact resistance
Compressive strength
Screw‑holding capability
Insert retention
Creep resistance
JLON 5002(L) contains 25% glass fiber and has a specified flexural strength of 170 MPa. Its nominal density is 1.8 g/cm³.
These properties can support a range of electrical components, but final suitability depends on the geometry and load conditions of the molded part.
For example, a large electrical cabinet cover needs sufficient stiffness to avoid excessive deflection. A busbar support requires mechanical strength and dimensional stability under combined electrical and thermal loads. A component containing metal inserts must resist cracking during molding, assembly and service.
Higher glass fiber content can improve stiffness and mechanical strength, but it may also affect material flow, surface appearance and fiber orientation. The appropriate glass fiber content should therefore be selected according to both performance requirements and molding conditions.
Low shrinkage is important for electrical components with:
Precise mounting holes
Metal inserts
Flat sealing surfaces
Long creepage paths
Tight assembly tolerances
Large covers or panels
Multiple integrated features
JLON 5002(L) is a low‑shrink Sheet Molding Compound. Low mold shrinkage can help reduce warpage, sink marks, dimensional variation and assembly problems.
Nevertheless, molded dimensions are not controlled by material formulation alone. They are also affected by:
Mold design
Charge pattern
Material flow
Fiber orientation
Molding pressure
Mold temperature
Curing time
Part ejection
Cooling conditions
For precision parts, customers should provide drawings and tolerance requirements so that the SMC material and molding process can be evaluated together.
The selected electrical‑grade SMC must fill the mold correctly and produce stable parts under the manufacturer’s actual equipment conditions.
Important processing information includes:
Press capacity
Mold dimensions
Mold temperature
Molding pressure
Curing cycle
Charge weight and charge pattern
Material flow distance
Minimum wall thickness
Deep ribs or complex features
Metal inserts
Surface‑quality requirements
An SMC formulation with insufficient flow may cause short filling, incomplete ribs, visible weld lines or trapped air. Excessive flow may increase fiber separation, resin‑rich areas, flash or non‑uniform mechanical properties.
JLON can evaluate or adjust SMC flow and formulation according to the customer’s component geometry and molding process, subject to technical validation and minimum order requirements.
The following data summarizes one JLON Sheet Molding Compound grade intended for electrical insulation and flame‑retardant applications.
Property | JLON 5002(L) |
|---|---|
Material | Sheet Molding Compound |
Primary application | Electrical insulation |
Glass fiber content | 25% |
Density | 1.8 g/cm³ |
Flexural strength | 170 MPa |
Heat Deflection Temperature | ≥200°C |
Dielectric strength | ≥12 kV/mm |
Comparative Tracking Index | ≥600 V |
Arc resistance | ≥180 seconds |
Mold shrinkage | Low shrinkage |
Water absorption | Low |
Flame classification | [TO BE ADDED] |
Test methods | [TO BE ADDED] |
The values above should be confirmed against the latest JLON technical data sheet. The final molded component should also be tested according to its applicable product standard.
Application | Important SMC properties | Additional considerations |
|---|---|---|
Meter boxes | Electrical insulation, flame retardancy and impact strength | Weather resistance, sealing and color stability |
Distribution enclosures | CTI, dielectric strength and dimensional stability | Outdoor exposure and wall thickness |
Busbar supports | CTI or PTI, arc resistance and mechanical strength | Creepage distance and temperature rise |
Switchgear parts | Arc resistance, flame retardancy and dielectric strength | Dimensional accuracy and thermal performance |
Circuit‑breaker housings | Arc resistance, heat resistance and mechanical strength | Complex mold flow and metal inserts |
Insulating barriers | Dielectric strength, flatness and flame retardancy | Thin sections and dimensional tolerances |
Terminal boards | Tracking resistance and dimensional stability | Hole positioning and insert retention |
Outdoor utility cabinets | Low water absorption and impact resistance | UV exposure, weathering and corrosion |
Transformer components | Electrical insulation and heat resistance | Thermal aging and humidity |
Railway electrical parts | Electrical and mechanical properties | Applicable flame, smoke and toxicity standards |
To help JLON recommend an appropriate Sheet Molding Compound, customers should provide as much of the following information as possible:
Component name and application
Drawing or 3D model
Indoor or outdoor use
Operating voltage
Continuous and maximum temperatures
Required CTI or PTI
Required dielectric strength
Required arc resistance
Flammability standard and classification
Mechanical‑property requirements
Part dimensions and wall thickness
Metal inserts or screw‑fixed areas
Required color and surface finish
Molding press capacity
Current molding conditions
Target technical data sheet
Required certifications
Estimated annual demand
If an existing material is being replaced, its technical data sheet and a molded sample can help JLON perform a preliminary comparison.
Replacement should be based on the relevant electrical, mechanical, thermal and processing properties rather than only on the commercial grade name.
Dielectric strength is important, but it does not represent every aspect of electrical insulation performance. CTI, arc resistance, moisture resistance, flame behavior and the finished component design must also be considered.
CTI and PTI describe related tracking tests but have different purposes. Customers should specify the correct test, required voltage and applicable standard.
HDT is a short‑term deformation test under a specified load. It does not independently define the material’s acceptable long‑term operating temperature.
Identical‑looking values may not be directly comparable when specimen thickness, conditioning, electrode configuration or test standards differ.
A technically suitable material can still produce defective parts if its flow and curing behavior do not match the mold and press.
An SMC formulation may be designed for flame resistance without holding the exact certification required for the final component. Always verify the test report, grade and tested thickness.
A meter box, busbar support and circuit‑breaker housing have different performance priorities. One electrical‑grade Sheet Molding Compound may not be suitable for every electrical insulation application.
JLON supplies SMC and BMC materials for electrical, industrial and structural applications.
Instead of offering only one fixed Sheet Molding Compound grade, JLON can work with customers to evaluate requirements including:
Electrical insulation
CTI and tracking resistance
Flame retardancy
Glass fiber content
Mechanical strength
Heat resistance
Mold shrinkage
Material flow
Surface quality
Color
Water absorption
Cost and production efficiency
Customers can provide a component drawing, target technical data sheet, existing sample or required test standard for preliminary grade evaluation.
JLON 5002(L) is one available electrical insulation and flame‑retardant SMC grade. Other Sheet Molding Compound formulations can be evaluated according to the final component and customer requirements.
Material selection and formulation adjustments remain subject to testing, production feasibility and final customer approval.
Sheet Molding Compound is a ready‑to‑mold thermoset composite containing resin, chopped fiber reinforcement, fillers and functional additives. It is generally processed by compression molding to produce strong and dimensionally stable parts with complex shapes.
No. Conventional SMC may provide some electrical resistance, but demanding electrical applications require verified dielectric strength, tracking resistance, arc resistance, flame performance and environmental durability.
The required CTI depends on operating voltage, pollution degree, creepage distance, component design and the applicable standard. A CTI of at least 600 V represents high tracking resistance, but it does not independently confirm finished‑component compliance.
Flame‑retardant SMC uses a resin and additive system designed to limit ignition or flame propagation. The claimed performance should always identify the test standard, classification and tested specimen thickness.
Yes. JLON can evaluate adjustments to glass fiber content, resin system, flame retardancy, shrinkage, flow, mechanical performance, electrical properties, color and surface quality according to the application and validation requirements.
SMC can provide electrical insulation, corrosion resistance, design integration and reduced maintenance compared with metal. Whether it can replace metal depends on structural loads, fire requirements, grounding design, installation environment and the applicable equipment standard.
Customers should provide the component drawing, required technical properties, application environment, molding conditions, color, certification requirements and estimated annual demand. If available, an existing technical data sheet or material sample is also helpful.
Choosing Sheet Molding Compound for electrical insulation requires a balanced evaluation of electrical, thermal, mechanical, environmental and processing performance.
Dielectric strength is important, but it should be considered together with CTI or PTI, arc resistance, flame retardancy, water absorption, heat resistance, mechanical strength, dimensional stability and molding behavior.
JLON 5002(L) provides 25% glass fiber, a density of 1.8 g/cm³, flexural strength of 170 MPa, HDT of at least 200°C, dielectric strength of at least 12 kV/mm, CTI of at least 600 V and arc resistance of at least 180 seconds.
JLON can also evaluate customized Sheet Molding Compound formulations according to specific electrical insulation, mechanical performance and molding requirements.
Send JLON your component drawing, operating voltage, required electrical properties, flame standard, molding conditions and annual demand. Our team will help evaluate a suitable SMC material for your electrical insulation application.
