An ASTM D178 Class 4 insulation mat is the highest-rated class in the ASTM D178 standard for electrical insulating rubber mats. It is designed to protect workers in the most demanding high-voltage electrical environments, where operating voltages reach up to 36,000 volts AC (36 kV).
Class 4 mats represent the pinnacle of electrical protection in the ASTM D178 range. They are tested to withstand 50,000 V (50 kV) dielectric voltage, making them the definitive choice for power transmission substations, EHV switchyards, and high-voltage testing laboratories that operate at or near 36 kV.
Technical Specifications of ASTM Class 4 Switchboard Mats
| ASTM Class | Class 4 |
| Max Use Voltage (AC) | 36.0 kV (36,000 V) |
| AC Proof Voltage | 40.0 kV (40,000 V) |
| Dielectric Withstand | 50.0 kV (50,000 V) |
| Recommended Thickness | 12.7 mm |
| Standard Roll Width | 1.0 m (customisable up to 1,220 mm) |
| Standard Roll Length | 10.0 m (max 15 m — above 6.4 mm) |
| Weight per Roll | Approx. 190 kg |
| Colour | Black (standard); custom colours on request |
| Anti-Skid Surface | Fine ribbed top, textured bottom |
| Material | Premium elastomer compound |
| Type | Type I (standard) | Type II (ozone, flame, oil resistant) |
| Product Code (Type I) | IM-ASTM-C4T1-BLAFT-12.7MM |
| Product Code (Type II) | IM-ASTM-C4T2-BLAFT-12.7MM |
Where is an ASTM D178 Class 4 Mat Used?
Class 4 mats are installed exclusively in the highest-voltage environments. They are the required choice for:
- Extra High Voltage (EHV) substations and transmission switchyards operating at 33 kV to 36 kV.
- National grid power transmission facilities and grid control rooms.
- High-voltage testing laboratories (circuit and equipment testing zones).
- Large-scale power generation plants like turbine hall HV areas.
- Offshore oil and gas platforms with primary HV distribution at 33 kV.
- Large aluminium smelting and steel plants with EHV supply networks.
- Rail electrification overhead equipment (OHE) depots and 25 kV supply points.
- Industrial facilities with direct 33 kV supply from the transmission grid.
If your site includes live work or switching operations near 33 kV to 36 kV equipment, Class 4 is the mandatory safety specification.
Why is Class 4 the Thickest ASTM D178 Mat?
At 12.7 mm, nearly half an inch, the Class 4 mat is the thickest in the range. This thickness is a direct result of the engineering requirements for 36 kV protection:
- Dielectric barrier: 12.7 mm of high-grade elastomer provides enough insulation depth to safely contain the electrical stress at 36 kV and pass the 50,000 V withstand test.
- No breakdown under proof testing: The entire roll surface is proof tested at 40,000 V, a test that a thinner mat at this class would fail.
- Mechanical robustness: At 190 kg per roll, Class 4 mats are built to withstand heavy industrial foot traffic, tool drops, and the mechanical wear of demanding substation environments.
- Superior comfort: The 12.7 mm cushion significantly reduces fatigue for maintenance engineers who may stand for hours during switching and maintenance operations.
Comparing All ASTM D178 Classes: For Quick Reference
| Class | Max Voltage | Proof Voltage | Withstand | Thickness | Weight/Roll |
| 0 | 1.0 kV | 5.0 kV | 10.0 kV | 3.2 mm | 42 kg |
| 1 | 7.5 kV | 10.0 kV | 20.0 kV | 4.8 mm | 68 kg |
| 2 | 17.0 kV | 20.0 kV | 30.0 kV | 6.4 mm | 92 kg |
| 3 | 26.5 kV | 30.0 kV | 40.0 kV | 9.5 mm | 140 kg |
| 4 | 36.0 kV | 40.0 kV | 50.0 kV | 12.7 mm | 190 kg |
Type I vs Type II: Class 4 Electrical Mats
At the Class 4 level, the choice of Type matters more than ever. These are environments with the highest electrical stress and often the harshest conditions:
- Type I Class 4: For EHV indoor switchgear rooms and substations with controlled environments.
- Type IIA Class 4: For outdoor switchyards where ozone from arc discharge and UV exposure can degrade standard rubber.
- Type IIB Class 4: For transmission substations and testing labs with significant arc flash and fire risk.
- Type IIC Class 4: For cable trenches, oil-filled equipment zones, and areas where hydraulic fluids may contact the mat.
All Type II variants can be combined (IIA + IIB + IIC) in a single Class 4 mat for maximum environmental protection.
Safety Compliance & Certifications
Duratuf AmeriVolt Class 4 mats meet and exceed global safety standards. Every batch is accompanied by a test certificate from internationally accredited laboratories.
How to Install & Handle ASTM Class 4 Mats
Due to its weight (approximately 190 kg per roll), Class 4 mats require careful handling:
- Use appropriate material handling equipment (trolleys, forklifts) for transport
- Lay flat with at least two people, never attempt solo installation
- Clean and inspect the floor surface thoroughly before laying
- Position to cover the entire work area, no gaps near live equipment
- No adhesive or tape is required because the mat’s weight and textured base keep it secure.
- Inspect before every use like cuts, tears or punctures in a Class 4 mat must be treated as a safety emergency.
- Store rolled (not folded) in a cool, dry, UV-protected environment.
AmeriVolt ASTM D178 Class 3 Insulation Mats are engineered for high-voltage installations. With ready stock across 7 warehouses in India and the UAE, we can ship fast to your project site anywhere in the world.
