Electrical Insulation Mats
Electrical systems that use AC or DC voltage, i.e., up to 66KV AC and 24V DC require the employer to provide an electrically insulated mat to protect the worker from electrocution.
Electrically insulated mats are generally used at electrical substations, lift machine rooms, transformer rooms, switchboard rooms, electrical panel areas, around bus bars, generator rooms, etc.
Classes of Electrical Insulation Mats
Standards for electrically insulated mats are stated under Indian Standard IS15652:2006. Under the standard, there are four classes of electrically insulated mats.
Class A – Maximum Use Voltage: 3.3 kV AC / 240V DC
Class B – Maximum Use Voltage: 11 kV AC
Class C – Maximum Use Voltage: 33 kV AC
Class D – Maximum Use Voltage: 66 kV AC
Class B, C, and D do not have a standardization for maximum use DC voltages but recommend that it is generally safe to use up to 1.4 times the corresponding AC voltage used.
These electrically insulated mats should also be resistant to acid, oil, and low temperatures. Mats are generally stamped or labelled by the manufacturer to indicate the class of the mats.
Electrically insulated mats should be manufactured from Elastomer (rubber), which must be free from any insertions that could lead to the deterioration of its insulating properties.
The upper surface of the mats is required to have small aberrations (i.e., a rough surface without edges) to avoid slippery effects. In contrast, the lower surface should be plane or could have an anti-slip resistant finish without affecting the dielectric property of the mat.
Manufacturers generally produce the mats in rolls that can vary in size from lengths ranging from 5,000mm and widths ranging from 1,000mm.
It is pertinent to note that the width of these electrically insulated mats varies according to the class of the mat.
Class A – Minimum thickness: 2.00mm
Class B – Minimum thickness: 2.50mm
Class C – Minimum thickness: 3.00mm
Class D – Minimum thickness: 3.50mm
Manufacturers of these mats are allowed a maximum tolerance of +/-10% in the nominal thickness of the specification of each class of mats.
There is no requirement/specification for the color of the mat. However, manufacturers can make them in a color of their preference using color additives without any metallic derivatives.
The standard specifies that for all the classes of the mats, the minimum insulation resistance with tap water (i.e., wet condition) will be 1,00,000 MΩ when measured with 5,000V Megger or 1,00,000 MΩ with 500V Megger.
The maximum leakage current specification for all the classes of mats when measures should also not exceed 10μA.
In addition, the material of these mats should have a suitable degree of flame retardance.
When purchasing an electrically insulated mat, a user must check that the mat is marked with the following:
- Class of the mat
- Manufacturer’s Lot No.
- Manufacturer’s Roll No.
- The Standard’s mark inscription
In the case of matting in rolls, the marking usually appears at least every meter underneath the mat.
An electrically insulated mat user should also exercise due care and diligence in maintaining it once it is in service. Mats should be regularly washed with normal water and soap to keep them clean. Petrol, diesel, grease, spirits, paints, thinners, chemicals, and alkalis should not be spilled onto the mat. In case of any accidental drop of such substances onto the mats, the mats should be cleaned up immediately.
Once these mats are put into service, they generally have an average lifespan that can range between 10 to 15 years under normal indoor working conditions unless damaged visually under any abnormal use. Therefore, it is usually recommended to do an annual visual inspection to check and record the condition of the mat. In addition, it is a good recommended practice to have the mat annually dielectrically tested. Should the mat fail its dielectric test, it should be removed from service.
One should always examine the mat for any damage that might affect the dielectric characteristics of the mat. If found, cracks, tears, or small pinholes should cause the mat to be removed from service and discarded.