4" PVC RMC

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Alwayslearningelec

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Hello. Have 40- 4" RMC PVC coated conduits running on roof about 500'. Would derating need ot be taken into consideration and how would that be calculated? Below is ther info. 500' on roof and 170' inside building.

Trip (A)Modeled LengthWirefill
2700670' - 7 1/4"4#600MCM CU+1#500MCM G
 
Look at this table in the 2008 NEC:

Table 310.15(B)(2)(c) Ambient Temperature Adjustment for Conduits Exposed to Sunlight On or Above Rooftops
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Alwayslearningelec said:
Interesting. Wonder why?
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This is the 2008 NEC, since then they have removed this table from the code so most of this roof nonsense is moot. Why XHHW is exempt is anyone's guess. If you need to comply with the 2008 requirement use XHHW.
 
Why are we referencing 2008 NEC? Is there even any jurisdictions still using 2008? That is a 16 year old document by now, and actually is getting close to 17 years since it was first released.
 
2023 NEC is simple, if raceway or cable is less than 3/4 inch above the roof, you need to add 30C to your outdoor temperature.

Note this means you still possibly need to make adjustments if your raceway/cable is 3/4 or more above the roof, all depends on what the outdoor temperature can be like in your application, there just isn't as much for extreme temp adders like they put in back in 2008 NEC.
 
kwired said:
Why are we referencing 2008 NEC? Is there even any jurisdictions still using 2008? That is a 16 year old document by now, and actually is getting close to 17 years since it was first released.
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The OP is in NYC which is on the 2008 NEC.
 
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