Cable Temp derating

Status
Not open for further replies.

edgmike

Member
Location
New Orleans
I have a cable, Gexol single conductor power cable, w/ a conductor ampacity at a temperature rating at 95deg C, 45 deg C ambient but I need to know what the overall derating is so I can select those cables at 90deg C operating and 40deg C ambient.

The NEC Table 310.16 has correction factors for Ambient Temp so I can adjust that from 45 down to 40deg. It also has the Temp Rating of Conductors at 60deg, 75deg, and 90deg but not 95deg. Not sure how to derate from 95deg C to 90deg C.

thx
 

bdarnell

Senior Member
Location
Indianapolis, IN
Occupation
Retired Engineer
You don't derate the cable's rating. It is what it is. What type cable is this ? Is it a mining cable or DLO or something along those lines ?

Either way, if you are using it in an NEC application, you have to select the cable's ampacity from the 75 deg. column. You can use the 90 deg. column for ampacity adjustment.
 

edgmike

Member
Location
New Orleans
It is very much like a DLO. Very flexible, finely stranded. We use them in the offshore industry, Class I, Div 1 or 2 depending on armored or unarmored.

The cable itself is good up to 110deg and 45deg (which look great on the manufactures ampacity table! 376A for a 4/0). The bus and DS breaker connectors are only good to 90deg and we are in a 40deg ambient so I wanted to determine how much current raises the operating temp of the cable to 90deg C in 40deg C ambient conditions to check vs table 310.16. I suspect 335A @ 95/45 will be very close to 237 at 90/40 per table 310.16.
 

Brookie

Member
Formula - Adjustment for Other Conditions

Formula - Adjustment for Other Conditions

Let's see if I can type this in a way that you can read it?

You can adjust ampacities from published data by using one of the following formulas:

For Copper Conductors

I' = I * Sqrt [(Tc'-Ta') / (Tc-Ta) * (234+Tc) / (234+Tc')]

For Aluminum Conductors

I' = I * Sqrt [(Tc'-Ta') / (Tc-Ta) * (228+Tc) / (228+Tc')]

Where: Tc = Conductor operating temperature (published)
Ta = Ambient temperature (published)
Tc' = Conductor operating temperature (corrected)
Ta' = Ambient temperature (corrected)
I = Ampacity (published)
I' = Ampacity (corrected)
 
Status
Not open for further replies.
Top