IEC 60112 - Battery Design

IEC 60112 is an international standard published by the International Electrotechnical Commission (IEC) that defines the test method for determining the comparative tracking index (CTI) and proof tracking index (PTI) of solid insulating materials. Tracking — the formation of conductive carbonised paths across an insulator surface due to electrical stress and contamination — is a critical failure mode in high-voltage electrical equipment including battery management systems, power electronics, and battery pack enclosures.

Published by: International Electrotechnical Commission (IEC)
Current edition: IEC 60112:2020 (5th edition)
Adopted as: EN IEC 60112:2020 (Europe), BS EN IEC 60112:2020 (UK)

Scope

IEC 60112 applies to solid electrical insulating materials used in the construction of electrical equipment. It is primarily used to characterise the resistance of insulating materials (plastics, composites, ceramics) to surface tracking under the combined influence of electric field and electrolyte contamination. The test method is applicable to materials used in battery pack enclosures, BMS PCBs, connector housings, cell holders, and busbars insulation.

CTI and PTI Explained

The comparative tracking index (CTI) is the numerical value of the voltage in volts at which a material withstands 50 drops of electrolyte solution without tracking failure. Materials are classified into groups based on their CTI value: Group I (CTI ≥ 600 V), Group II (400 ≤ CTI < 600 V), Group IIIa (175 ≤ CTI < 400 V), and Group IIIb (100 ≤ CTI < 175 V). Higher CTI values indicate better tracking resistance and allow reduced creepage distances in equipment design.

The proof tracking index (PTI) is a pass/fail test verifying that a material withstands a specified voltage for a specified number of drops — used when a specific voltage threshold must be confirmed rather than the full CTI curve established.

Relevance to Battery Engineering

IEC 60112 CTI values are referenced in safety standards such as IEC 62368-1, IEC 60664-1, and UL 508 to determine required creepage distances between conductors on PCBs and in enclosures. For battery system designers, knowledge of the CTI group of insulating materials used in BMS PCBs, connector housings, and pack enclosures is essential for meeting the clearance and creepage requirements in product safety standards. Selecting materials with higher CTI ratings can reduce required creepage distances, enabling more compact designs at higher voltages.

Disclaimer: This is not a definitive guide, just an indication and it is important that you always go back to the source for legislation.