Power Cable Ampacity Correction

[pristava]

Is it necessary to provide Cable Ampacity Derating factors for the ambient temperature of 105 deg.F or 40 deg.C inside Chemical Plant Building. ( conductor 90degC)
I am in Canada where Canadian Electrical Code provides factors 0.87-0.90 but other engineers are not accepting that idea.
Thanks.

 

[davidbeach]

I don't know the CEC, but the NEC would require derating. I couldn't say how often that derating is actually applied.

 

[wareagle]

The NEC requires that the ampacity be derated because table 310.16 give the ampacity of conductors at 30C 86F.
When the temp rises to 40 C you must derate.
The factors for 40C are for different insulations as follows:
60C conductor 0.82
75C conductor 0.88
90C conductor 0.91.
If you are using 90C/75C conductor you may derate using the 0.91 factor but the resultant ampacity may not exceed the 75C rating.

 

[wareagle]

"I am in Canada where Canadian Electrical Code provides factors 0.87-0.90 but other engineers are not accepting that idea."
Why won't the engr's accept derating?

 

[pristava]

Why won't the engr's accept derating?
Good Question. Existing part of the plant has area with that temperature where derating has not been provided. Also owner of the building is not accepting derating.
Generally I agrre with you that derating must be provided.

 

[cuky2000]

Enforcement of the CEC... Electrical Inspectors and Chief Electrical Inspectors enforce standards through design reviews, inspections, investigations, etc. Penalties can range from fines of tens of dollars to several thousands of dollars depending on the nature of the infraction.

Suggestion: Propose to your client to obtain an independent opinion to clarify possible code violation and determine the liability implications for the plant and for the professional engineers taking exception applying temperature derating factor to the cable.

Good luck