Many insulative properties of polyamides depend on the moisture content and temperature of the material. For this reason, actual operating conditions should always be taken into account. As with flame retardancy, many different, local test standards are available. Here is an overview of the major international tests.

Volume resistivity
The volume resistivity shows the resistance of a material to the flow of current. It can be measured according to different test standards; the values mentioned here are measured according to ISO 1325. Graph 1 shows the volume resistivity of Polynil P50L versus temperature, whereas graph 2 illustrates the effect of moisture.


Comparative Tracking Index (CTI)
The comparative tracking index (IEC 112 or UL746) is carried to test the resistance of plastics against superficial tracking currents under humid conditions. The maximum voltage that can be measured in this test is 600V; Polyamides exhibit excellent CTI values.

On the UL card, the PLC's are given to the the CTI:
>600 V: PLC 0
400-600 V: PLC 1
250-400V: PLC 2
175-250V: PLC 3
100-175 V: PLC 4
<100V: PLC 5

Di electric strength
The di-electric strength is the voltage at which the insulative properties of a material are destroyed. An arc passes through the material at this point. The di-electric strength is depended on temperature, moisture content and wall thickness. The graph below illustrates the effect of temperature.