Power resistor

How am I supposed to read this resistor thermal rating graph?

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Currently trying to learn to read resistor datasheet, specifically thermal rating.
I want to have a general idea of what the temperature of resistor will be at certain power.

First question is, is there some place I can look up and learn to read resistor datasheet in detail ?

Second, I found these graphs online, when looking to buy a resistor I need, and I am having trouble understanding the graphs or I am unsure to what they represent exactly, can you help out ?

Here are the graphs :

This is graph 1, power consumption curve is unclear to me 

This is graph 2, power reduction curve and surface temperature are unclear

Graph 2



asked 38 mins ago

komrad2236's user avatar


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  • 2Those curves show that if the ambient temperature gets higher you can’t dissapiate as much power as at room temperature without overheating the resistor. The value is given in % of rated power. – kruemi 29 mins ago
  • I agree with @komrad2236. So for example, for resistor (100W 4Ω), max voltage V40c you can apply at room temperature below 40C is Power40c = V40c x I40c = (V40C ** 2) / 4Ω. Now at temperature 220C, P220c = 20% of P40c, … – tlfong01 2 mins ago  Edit  

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