The insulated sheet is checked for dielectric strength as follows:
| Thickness | Dielectric strength |
|---|---|
| 2.0 mm | 30 kV |
| 2.5 mm | 45 kV |
| 3.0 mm | 65 kV |
The proof voltage checked for different mat thicknesses is as follows:
| Thickness | Proof voltage |
|---|---|
| 2.0 mm | 10 kV |
| 2.5 mm | 20 kV |
| 3.0 mm | 36 kV |
The mat is checked at these voltages in direct contact with water. This proves how safe the mat is even during faults of any type occurring during operation and handling of switchgear and allied equipment.
In the event of a fault, arc current does not flow through the mat — it takes the path outside the mat.
All the above tests are conducted through the Central Power Research Institute (CPRI), Government of India — the country's premier testing lab for electrical equipment. These insulated mats are also specified in CPWD Specifications Part IV for sub-stations, making their use mandatory for the protection and safety of workmen.