Comparative Tracking Index

The Comparative Tracking Index or CTI is used to measure the electrical breakdown (tracking) properties of an insulating material. Tracking is an electrical breakdown on the surface of an insulating material wherein an initial exposure to heat chars the material, and the char is more conductive than the original insulator, producing more current flow, more heat, and eventually complete failure.


A large voltage difference gradually creates a conductive leakage path across the surface of the material by forming a carbonized track. Testing method is specified in IEC standard 60112.

To measure the tracking, 50 drops of 0.1% ammonium chloride solution are dropped on the material, and the voltage measured for a 3 mm thickness is considered representative of the material performance. Also term PTI (Proof Tracking Index) is used: it means voltage at which during testing on five samples the samples pass the test with no failures.

Performance Level Categories (PLC) were introduced to avoid excessive implied precision and bias.

The CTI value is used for electrical safety assessment of electrical apparatus, as for instance carried out by Underwriters Laboratory in USA and many other laboratories in the world. The minimum required creepage distances over an insulating material between electrically conducting parts in apparatus, especially between parts with a high voltage and parts that can be touched by human users, is dependent on the insulator's CTI value. Also for internal distances in an apparatus by maintaining CTI based distances, the risk of fire is reduced.

Creepage distance requirement depends on the CTI. Material which CTI is unknown are classified in IIIb group. There's no CTI requirement for glass, ceramic, and other inorganic material which don't breakdown on surface.

The better the insulation, the higher the CTI (positive relationship). In terms of clearance, a higher CTI value means a lower minimum creepage distance required, and the closer two conductive parts can be. [1]

Tracking Index (V) PLC
600 and Greater 0
400 through 599 1
250 through 399 2
175 through 249 3
100 through 174 4
< 100 5

In design of medical products, the CTI is treated differently. Material groups are classified as shown below, per IEC 60601-1:2005, International Standard published by the International Electrotechnical Commission:

Comparative Tracking Index (CTI) Material Group
600 ≤ CTI I
400 ≤ CTI < 600 II
175 ≤ CTI < 400 IIIa
100 ≤ CTI < 175 IIIb


  1. ^ "Tech Brief Comparative Tracking Index" (PDF). Retrieved January 29, 2018.

External links

  • Underwriters Laboratory definition of CTI [1]
  • IEC 60601-1:2005 Medical electrical equipment - Part 1: General requirements for basic safety and essential performance [2]
  • IEC 61010-2-033:2012 specifies safety requirements for METERS. The METERS that have a primary purpose of measuring voltage on a live MAINS CIRCUIT [3]
Aluminium diethyl phosphinate

Aluminium diethyl phosphinate is a chemical compound with formula Al(C4H10O2P)3. It decomposes above 300 °C.

CAMPUS (database)

CAMPUS (acronym for Computer Aided Material Preselection by Uniform Standards) is a multilingual database for the properties of plastics. It is considered worldwide as a leader in regard to the level of standardization and therefore, ease of comparison, of plastics properties. It also supports diagrams to a large extent. CAMPUS is based on ISO standards 10350, for single-point value e.g. the density, and 11403, for diagrams, e.g. the Stress–strain curve.

Electrical breakdown

Electrical breakdown or dielectric breakdown is when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event (as in an electrostatic discharge), or may lead to a continuous arc if protective devices fail to interrupt the current in a power circuit.

Under sufficient electrical stress, electrical breakdown can occur within solids, liquids, gases or vacuum. However, the specific breakdown mechanisms are different for each kind of dielectric medium.

Nylon 66

Nylon 66 (nylon 6-6, nylon 6/6 or nylon 6,6) is a type of polyamide or nylon. There are many types of nylon: the two most common for textile and plastics industries are nylon 6 and nylon 66. Nylon 66 is made of two monomers each containing 6 carbon atoms, hexamethylenediamine and adipic acid, which give nylon 66 its name.


Plastic is material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and so can be molded into solid objects.

Plasticity is the general property of all materials which can deform irreversibly without breaking but, in the class of moldable polymers, this occurs to such a degree that their actual name derives from this specific ability.

Plastics are typically organic polymers of high molecular mass and often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, however, an array of variants are made from renewable materials such as polylactic acid from corn or cellulosics from cotton linters.Due to their low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in a multitude of products of different scale, including paper clips and spacecraft. They have prevailed over traditional materials, such as wood, stone, horn and bone, leather, metal, glass, and ceramic, in some products previously left to natural materials.

In developed economies, about a third of plastic is used in packaging and roughly the same in buildings in applications such as piping, plumbing or vinyl siding. Other uses include automobiles (up to 20% plastic), furniture, and toys. In the developing world, the applications of plastic may differ—42% of India's consumption is used in packaging.Plastics have many uses in the medical field as well, with the introduction of polymer implants and other medical devices derived at least partially from plastic. The field of plastic surgery is not named for use of plastic materials, but rather the meaning of the word plasticity, with regard to the reshaping of flesh.

The world's first fully synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term 'plastics'. Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger who has been called "the father of polymer chemistry" and Herman Mark, known as "the father of polymer physics".The success and dominance of plastics starting in the early 20th century led to environmental concerns regarding its slow decomposition rate after being discarded as trash due to its composition of large molecules. Toward the end of the century, one approach to this problem was met with wide efforts toward recycling.

Polybutylene terephthalate

Polybutylene terephthalate (PBT) is a thermoplastic engineering polymer that is used as an insulator in the electrical and electronics industries. It is a thermoplastic (semi-)crystalline polymer, and a type of polyester. PBT is resistant to solvents, shrinks very little during forming, is mechanically strong, heat-resistant up to 150 °C (or 200 °C with glass-fibre reinforcement) and can be treated with flame retardants to make it noncombustible. It was developed by Britain's Imperial Chemical Industries (ICI).PBT is closely related to other thermoplastic polyesters. Compared to PET (polyethylene terephthalate), PBT has slightly lower strength and rigidity, slightly better impact resistance, and a slightly lower glass transition temperature. PBT and PET are sensitive to hot water above 60 °C (140 °F). PBT and PET need UV protection if used outdoors, and most grades of these polyesters are flammable, although additives can be used to improve both UV and flammability properties.

IEC standards
ISO/IEC standards

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.