Derating wires in conduit.

[ted stringfellow]

When derating wires in conduit does it matter if conduit is horizontal or vertical? Also does it matter if the load is continuous? If so, can you tell me the code section? thanks.

 

[A/A Fuel GTX]

No and No. Conductors for continuous loads are already adjusted by the 1.25% rule.

 

[raider1]

I agree with Fuel, 310.15(B)(3)(a) does not consider vertical VS horizontal nor continuous VS non-continuous.

Chris

 

[G._S._Ohm]

A vertical conduit may have convection air currents which should make some difference, but evidently too small for NEC purposes.

 

[ted stringfellow]

derate

derate

Thank You for the replies.Was thinking without a continious load there would be less heat build up also with vertical conduit the
wire is not laying in bottom,less heat.The installation has a 2 inch conduit,33 inches long.Has 6# 10,2#8 and 4# 12

 

[Dennis Alwon]

Thank You for the replies.Was thinking without a continious load there would be less heat build up also with vertical conduit the
wire is not laying in bottom,less heat.The installation has a 2 inch conduit,33 inches long.Has 6# 10,2#8 and 4# 12

I understand your thinking on this but the NEC has never approached it since it would be hard to know if the conduit wouldn't have conductors clumped to one side or not.

 

[jusme123]

Thank You for the replies.Was thinking without a continious load there would be less heat build up also with vertical conduit the
wire is not laying in bottom,less heat.The installation has a 2 inch conduit,33 inches long.Has 6# 10,2#8 and 4# 12

Conduit size is not a factor when derating, these same conductors you have listed above could be installed in a 4" conduit, the derating will be exactly the same.