Why is SEU different amperage than Romex ?

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Stevenfyeager

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United States, Indiana
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electrical contractor
Why is SEU or SER different amperage rating than Romex ? Why are the SE cables rated higher than Romex ? SE uses the 75 column and NM uses the 60 column, am I right ? They are both jacketed. Just different type of insulation ? With 6-3 Cu costing $ 5 to $ 6 per foot here, does anyone use #4 SER for ranges now ? ($1.25 ft) (Both rated for 55 amps?) Thank you.
 
Stevenfyeager said:
Why is SEU or SER different amperage rating than Romex ? Why are the SE cables rated higher than Romex ? SE uses the 75 column and NM uses the 60 column, am I right ? They are both jacketed. Just different type of insulation ? With 6-3 Cu costing $ 5 to $ 6 per foot here, does anyone use #4 SER for ranges now ? ($1.25 ft) (Both rated for 55 amps?) Thank you.
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Said this recently in another thread on the topic, but Ive been using #6 SER pretty much my entire 22 year career. Hardly ever used 6 or 8 NM even pre covid.
 
Stevenfyeager said:
Why is SEU or SER different amperage rating than Romex ? Why are the SE cables rated higher than Romex ? SE uses the 75 column and NM uses the 60 column, am I right ? They are both jacketed. Just different type of insulation ? With 6-3 Cu costing $ 5 to $ 6 per foot here, does anyone use #4 SER for ranges now ? ($1.25 ft) (Both rated for 55 amps?) Thank you.
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One possibility is that NM cable is most commonly used where the small conductor rule applies anyway. SER is conductor type more likely to be used on large scale feeders while NM cable is more likely to be used on 30A and less circuits.
 
Not necessarily an answer, but in residential the smaller sizes (14-12-10) where you see NM, the 240.4 ampacity restrictions which apply to most of your terminations, regulate those sizes to their 60° rating anyway
 
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