# Motor Winding Insulation Life vs Temperature Calculator > Source: https://netray.co/tools/motor-winding-insulation-life-temperature-calculator > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Thermal margin and expected insulation life of a motor from class, ambient, rise and hot spot allowance, with an ambient sweep. ## Category maintenance ## Industry Manufacturing ## Audience - Reliability engineer - Electrical maintenance - Condition monitoring analyst ## Tool **Kind:** calculator **Inputs:** #### Insulation class limit **Key:** class_temp **Type:** select **Default:** 155 **Options:** ##### Class B (130 C) **Value:** 130 ##### Class F (155 C) **Value:** 155 ##### Class H (180 C) **Value:** 180 #### Ambient temperature **Key:** ambient **Type:** number **Default:** 40 **Min:** -20 **Max:** 100 **Step:** 1 **Unit:** C #### Measured winding temperature rise **Key:** rise **Type:** number **Default:** 85 **Min:** 0 **Max:** 200 **Step:** 1 **Unit:** C **Help:** Average rise, for example from resistance method or thermal imaging with correction. #### Hot spot allowance **Key:** hotspot **Type:** number **Default:** 10 **Min:** 0 **Max:** 30 **Step:** 1 **Unit:** C **Help:** Difference between average winding and hottest spot. #### Design life at class limit **Key:** base_life **Type:** number **Default:** 20000 **Min:** 1000 **Step:** 1000 **Unit:** h **Help:** Commonly quoted around 20,000 h at the rated limit; confirm with the motor maker. #### Operating hours per year **Key:** hours_year **Type:** number **Default:** 7500 **Min:** 100 **Max:** 8760 **Step:** 100 **Unit:** h **Outputs:** #### Estimated hot spot temperature **Key:** hot **Expr:** ambient + rise + hotspot **Format:** decimal **Description:** Degrees C. #### Margin to class limit **Key:** margin **Expr:** class_temp - hot **Format:** decimal **Description:** Negative means the winding runs above its class. #### Life multiplier **Key:** multiplier **Expr:** pow(2, (class_temp - hot) / 10) **Format:** decimal #### Expected insulation life **Key:** life_h **Expr:** base_life * multiplier **Format:** integer **Primary:** true #### Expected life in years **Key:** life_y **Expr:** life_h / hours_year **Format:** decimal **Primary:** true **Chart:** #### Expected insulation life (hours) vs ambient temperature **Type:** line **X:** ambient **From:** 20 **To:** 70 **Steps:** 26 **Series:** - life_h **Disclaimer:** The halving-per-10-degrees rule is a rule of thumb from Arrhenius ageing. Real life also depends on voltage stress, moisture, contamination and starts. ## Content **Intro:** Heat is the main ageing agent for motor insulation. As a rule of thumb, every 10 degrees C above the rated temperature roughly halves insulation life, and every 10 degrees below roughly doubles it. This tool turns your temperature readings into a life estimate. **Sections:** #### How to use it **Body:** Pick the insulation class from the nameplate. Enter the ambient temperature at the motor, the measured winding rise and an allowance for the hot spot, which is higher than the average winding temperature. The calculator reports the hot spot, the margin to the class limit, the life multiplier and the expected life in hours and years. The chart shows how a hot summer or blocked ventilation changes the outlook. #### The method **Body:** Insulation ageing follows the Arrhenius relationship, which gives an approximately exponential link between temperature and life. The rule of thumb simplifies it to life = base life x 2 to the power ((class limit - hot spot) / 10). Class B, F and H limits are 130, 155 and 180 degrees C. Many motors are specified with a lower rise than their class permits, which gives extra life margin that this tool shows. **Bullets:** - Class F motor used at class B rise gains very large life margin - High ambient, dust, blocked fins and voltage imbalance all erode the margin - Use thermography as an indicator, then confirm with winding resistance #### Common mistakes **Body:** Reading the case temperature and treating it as winding temperature will understate the heat inside. Ignoring ambient above 40 degrees C, running on a variable frequency drive without checking cooling at low speed, and ignoring repeated starts are other frequent mistakes. Treat the estimate as a ranking tool to find motors that deserve attention, not as a prediction of failure date. **Bullets:** - Using case temperature as winding temperature - Forgetting derating at altitude or high ambient - Ignoring low-speed cooling on drives **Cta:** Netray can combine motor nameplate data from your ERP asset register with temperature readings to rank motors by thermal margin. **Faq:** #### What is the 10 degree rule for motors? **Answer:** It states that insulation life roughly halves for every 10 degrees C of sustained operation above the rated temperature and doubles for every 10 degrees below. It is an approximation of Arrhenius ageing. #### What are the insulation class temperatures? **Answer:** Class B is 130 degrees C, Class F is 155 degrees C and Class H is 180 degrees C maximum winding temperature. Usable rise is lower once ambient and hot spot allowances are taken off. #### Can I trust the life figure? **Answer:** Treat it as a relative indicator. Voltage spikes from drives, moisture, vibration and start frequency can shorten life well beyond what temperature alone suggests. #### How do I measure winding temperature? **Answer:** The resistance method gives average winding temperature. Embedded RTDs or PTC sensors give direct readings. Infrared on the frame is only a rough proxy and needs correction. ## Search terms motor insulation life calculator, 10 degree rule motor winding life, insulation class temperature limits, motor winding temperature life halves, thermal life of electric motor, class F class B insulation life, motor overheating life estimate, motor temperature rise calculator --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json