Relative Thermal Index (RTI), Thermal Index (TI), and Long Term Thermal Aging (LTTA) for Materials Testing
Relative Thermal Index & Thermal Index Tests
ELTEK Labs conducts a wide range of thermal index tests to various industry standards.
- Relative Thermal Index (RTI) refers to thermal classification of a material by comparing the performance of a new (candidate) material against the performance of a known or reference material. Two materials are involved.
- Thermal Index (TI) refers to thermal classification of a material by projecting the pattern (thermal aging curve) to a pre-selected time coordinate; not a known or reference material. Only the candidate material is involved.
- Thermal Index testing, RTI or TI, is intended to evaluate thermal decomposition as the only, or main, cause of loss of performance property.
General Information
This general category must be separated into specific type of materials as each sub-group has different performance properties and requirements.
The industry has identified three essential properties which can result in establishing thermal classifications for various types of materials. Not all three properties are related to all sub-categories. The pattern of properties and the sub-categories is as follows.
Three Essential Properties
| Electrical | Mechanical, Tensile or Flexural | Impact | |
| Polymeric Materials / Plastics / Engineering Polymers | X | X | X |
| Injection Molding Resins | X | X | X |
| Film / Paper / Tape | X | X | |
| Laminated / Composite Sheet | X | X | |
| Powder Coatings | X | ||
| Photovoltaic Back Sheets | X | X | Tear Resistance |
| Photovoltaic Top Sheet | Under industry review to determine the correct test methods | ||
| Magnet Wire Coatings | X | ||
| Magnet Wire | X | ||
| Insulating Varnishes/ Impregnating Resins | X | X | |
| Single and Multi-layered Wire | X | ||
| Sleevings and Tubings | X | ||
Special Note: Flammability Rating may be necessary for some categories of RTI or TI evaluations.
ELTEK Labs tests all types of polymeric materials such as films, papers, tapes, laminated sheets, composite sheets, rigid sheets and many others types.
ELTEK Labs conducts Relative Thermal Index [RTI] and Thermal Index [TI] tests using the Fixed Time Frame Method or the Fixed Temperature Method in accordance with:
International Electrotechnical Commission [IEC]
IEC 60216-6: Ed. 2.0: Electrical insulating materials – Thermal endurance properties
- Part 6: Determination of thermal endurance indices (TI and RTE) of an insulating material using the fixed time frame method
IEC 60216-5: Electrical insulating materials – Thermal endurance properties
- Part 5: Determination of relative thermal endurance index (RTE) of an insulating material
IEC 60216-1: Electrical insulating materials – Thermal endurance properties
IEC 60216: Electrical insulating Materials – Thermal Endurance Properties
- Part 2: Determination of thermal endurance properties of electrical insulating materials
IEC 60172: Test Procedure for the Determination of the Temperature Index of Enameled Winding Wires
IEC 60243: Electrical Strength of Insulating Material – Test methods
- Part 1: Tests at Power Frequencies (This test method is structured for both Relative Thermal Index and Thermal Index)
IEC 61857: Electrical Insulation Systems – Procedures for thermal evaluation
- Part 1: General requirements – Low Voltage
- Part 21: Specific requirements for general-purpose models – Wire-wound applications
To arrange thermal index testing, request a quote online now or call 636-949-5835.
International Standards Organization [ISO]
ISO 180: Plastics – Determination of Izod Impact Strength (This test method is structured for both Relative Thermal Index and Thermal Index)
ISO 527: Plastics – Determination of Tensile Properties (This test method is structured for both Relative Thermal Index and Thermal Index)
ISO 178: Plastics – Determination of Flexural Properties (This test method is structured for both Relative Thermal Index and Thermal Index)
ISO 8256: Plastics – Determination of Tensile-Impact Strength (This test method is structured for both Relative Thermal Index and Thermal Index)
To arrange thermal index testing, request a quote online now or call 636-949-5835.
UL
UL Standards are more focused on the structure of thermal aging projects while organizations such as ASTM are focused on the test methodologies to evaluate the properties.
UL 746-B: Polymeric Materials – Long Term Properties
- Plastics: All sections
- Mechanical without Impact
- Mechanical with Impact
- Electrical
- Polypropylene: Section 20.2
- Powder Coating: Section 20.3 tested applied over steel
- Bus Bar Insulation: Section 20.3 tested applied over copper and/or aluminum
- Films and Papers: Section 15
UL 1446: Insulation Systems – General
- Magnet Wire Coating
- Magnet Wire for full thermal aging
- Magnet Wire for 1-temperature aging
- Varnishes / Impregnating Resins
- EIS for full thermal aging (refer to our EIS section of our website)
- EIS 1-temperature and/or 2-temperature (refer to our EIS section of our website)
UL 1441: Sleeving
UL 224: Tubing
UL 5703: Determination of the maximum Operating Temperature Rating of Photovoltaic (PV) Backsheet Materials
To arrange thermal index testing, request a quote online now or call 636-949-5835.
American Society for Testing of Materials [ASTM]
ASTM method D-2304: Standard Test Method for Thermal Endurance of Rigid Electrical Insulating Materials
ASTM method D-149: Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-256: Standard test Methods for Determining the Izod Pendulum Impact Resistance of Plastics (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-638: Standard Test Method for Tensile Properties of Plastics (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-790: Standard Test Methods for Flexural Properties of Unreinforced and reinforced Plastics and Electrical Insulating Materials (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-882: Standard Test Method for Tensile Properties for Thin Plastic Sheeting (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-1822: Standard Test Method for Tensile-Impact Energy to Break Plastics and Electrical Insulating Materials (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-3801: Standard Test Method for Measuring the Comparative Burning Characteristics of Solid Plastics in a Vertical Position (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-6272: Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials from Four-Point Bending (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-2307: Standard Test Method for the Thermal Endurance of Round Magnet Wire (This test method is structured for Thermal Index)
ASTM method D-3251: Standard Test Method for the Thermal Endurance Characteristics of Electrical Insulating Varnish Applied Over Film-Insulated Magnet Wire (This test method is structured for Thermal Index)
ASTM method D-4881: Standard test Method for Thermal Endurance of Varnished Fibrous- or Film- Wrapped Magnet Wire
ASTM method D-3145: Standard Test Method for Thermal Endurance of Electrical Insulating Varnishes by the Helical Coil Method (This test method is structured for Thermal Index)
ASTM method D-1932: Standard Test Method for Thermal Endurance of Flexible Electrical Insulating Varnishes. (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-1830: Standard Test Method for Thermal Endurance of Flexible Sheet Materials used for Electrical Insulation by the Curved Electrode Method (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-695: Standard Test Method for Compressive Properties of Rigid Plastics (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-1938: Standard Test Method for Tear-propagation of Plastic Film and Thin Sheeting by a Single-Tear Method (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-2288: Weight Loss of Plasticizers on Heating (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM practice D-3045: Standard Practice for Heat Aging of Plastics Without Load (This test method is structured for both Relative Thermal Index and Thermal Index)
ASTM method D-1876-01: Standard Test Method for Peel Resistance of Adhesives (This test method is structured for both Relative Thermal Index and Thermal Index)
To arrange thermal index testing, request a quote online now or call 636-949-5835.
National Electrical Manufacturers Association [NEMA]
NEMA MW 1000: Magnet Wire; section 3.58: Thermal Endurance (This test method is structured for Thermal Index)
To arrange thermal index testing, request a quote online now or call 636-949-5835.
