PTR Hartmann

Insulation Material Groups

(in accordance with EN 60664-1:2007 and VDE 0110-1)

For the purposes of the above mentioned standards, materials are classified into four groups according to their CTI values. These values are determined in accordance with IEC 60112 using solution A. The groups are as follows:

  • Insulation materials group I               600 ≤ CTI 
  • Insulation materials group II              400 ≤ CTI < 600 
  • Insulation materials group IIIa           175 ≤ CTI < 400 
  • Insulation materials group IIIb           100 ≤ CTI < 175. 

The proof tracking index (PTI) is used to verify the tracking characteristics of materials. A material may be included in one of these four groups on the basis that the PTI is not less than the lower value specified for the group