Question 1

What is an IEC 61039 classification code?

Accepted Answer

IEC 61039:2025 assigns an insulating liquid a code of the form CLASS–CATEGORY–NUMBER, e.g. L-NTUO-2960121. L is the class (lubricants/industrial oils); the four category letters give family (N, electrical insulation), application (T/C/S/Y), antioxidant (U/I) and fire point (O/K/L); the seven digits encode the reference standard, a sub-class, net calorific value, lowest cold-start temperature and biodegradability.

Question 2

What do the fire-point letters O, K and L mean?

Accepted Answer

O is a fire point below 300 °C, K is a fire point at or above 300 °C (the less-flammable esters and silicones), and L means the fire point is not detectable. Per the published IEC 61039:2025 (Clause 5.3) exactly 300 °C falls in the K class.

Question 3

How do I read L-NTUO-2960121?

Accepted Answer

L = lubricant class; N = electrical insulation; T = transformer application; U = uninhibited (no antioxidant); O = fire point < 300 °C; 296 = IEC 60296 (mineral oil); 0 = no sub-class; 1 = net calorific value ≥ 42 MJ/kg; 2 = cold-start temperature 0 to −10 °C; 1 = inherently biodegradable.

Question 4

Is "K-class" the same as the class letter?

Accepted Answer

No. "K-class" is colloquial. The formal class is L; K is only the fourth category letter (fire point ≥ 300 °C). The tool keeps this distinction explicit.

Question 5

Where does the data come from?

Accepted Answer

Every letter, digit boundary and worked-example code reproduces IEC 61039:2025 (Ed 3) Clauses 5.2–5.4 and Table 2. Values that the standard does not define (e.g. an "unknown" net calorific value) are shown as a "?" placeholder and the code is flagged incomplete rather than guessed.

IEC 61039 Insulating-Liquid Code

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Methodology

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IEC 61039 Insulating-Liquid Code

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Methodology

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