Ambinet Air Temperature for Conductor Derating
Ambinet Air Temperature for Conductor Derating
(OP)
Looking to see if the 24 hour average ambient temperature can be used for conductor derating or do I need to use the maximum ambient temperature seen at ay given time (even tho it may only be for 5 minutes as an example.
I assume if I need to use the maximum ambient temperature the thermal time constant for 600v conductors is low.
Thanks.
b
I assume if I need to use the maximum ambient temperature the thermal time constant for 600v conductors is low.
Thanks.
b






RE: Ambinet Air Temperature for Conductor Derating
RE: Ambinet Air Temperature for Conductor Derating
RE: Ambinet Air Temperature for Conductor Derating
or:
IEEE 242/2001 CH.9.5.2.4 Development of intermediate characteristics:
“Cable, with the thermal inertia of its own and of its surroundings, takes from 1 h to 6 h to change from initial to final temperature as the result of a current change. Consequently, overloads substantially greater than its continuous rating may be placed on a cable for this range of times.”
If the 600 V cable lays on a free air-on racks, for instance-a cable of less than 2 awg the thermal constant K is only 20 min [0.33 h] but a cable with copper conductor more than 250 MCM directly buried in ground K will be 6 hours.
By-the-way, in my opinion IEEE 399 does not specifies the maximum ambient temperature but it indicates usual limits. The following chapter states the adjustment factors if the ambient could be different from “usual":
IEEE 399/1997 ch.13.4 Ampacity adjustment factors.