Application of 110.14(C)(1)(b) and 215.2(A)(1) in Conductor sizing

[UnfortunatePotato]

Problem:

• I am trying to choose a 90°C conductor to land on my 75°C terminals.

Givens:

• Equipment is 75°C rated.
• Equipment terminals are 75°C rated.
• Wire insulation is 90°C rated.
• Continuous load
• 40°C ambient temperature
• 4 current carrying conductors

Thought Process:
I am allowed to use a 90°C conductor according to 110.14(C)(1)(b)(2)

I follow the 215.2(A)(1) to determine my conductor derate:

• 215.2(A)(1)(a): The load is continuous so I need at least a 0.8 derate (which is the inverse of 125%).
• 215.2(A)(1)(b):
  • 40°C ambient temperature on 90°C conductor is 0.91 derate from Table 310.15(B)(2)(a).\
  • 4 current-carrying conductors results in 0.8 derate from Table 310.15(B)(3)(a).
  • Multiplying these together results in 0.728 derate.

Taking the more conservative derate according to 215.2(A)(1) means my conductor ampacity derate needs to be 0.728. Now, because I am using 90°C conductor on a 75°C terminal the derates apply to the 90°C column in 310.15(B)(16). Finally, my interpretation of 110.14(C) says that this wire can only be used so long as the derated conductor ampacity results in a lower ampacity than the 75°C

From 110.14(C)
The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correct, or both.

From 110.14(C)(1)(b)(2)
Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors.

Is this a correct understanding and application of conductor ampacity derates? In a situation where my combined ambient + CCC derate is lower than 0.8, then is it also correct to apply the continuous current derate to the 90°C wire and check that against the 75°C entry?

 

[SSDriver]

You are close but

Problem:

• I am trying to choose a 90°C conductor to land on my 75°C terminals.

Givens:

• Equipment is 75°C rated.
• Equipment terminals are 75°C rated.
• Wire insulation is 90°C rated.
• Continuous load
• 40°C ambient temperature
• 4 current carrying conductors

Thought Process:
I am allowed to use a 90°C conductor according to 110.14(C)(1)(b)(2)

I follow the 215.2(A)(1) to determine my conductor derate:

• 215.2(A)(1)(a): The load is continuous so I need at least a 0.8 derate (which is the inverse of 125%).
• 215.2(A)(1)(b):
  • 40°C ambient temperature on 90°C conductor is 0.91 derate from Table 310.15(B)(2)(a).\
  • 4 current-carrying conductors results in 0.8 derate from Table 310.15(B)(3)(a).
  • Multiplying these together results in 0.728 derate.

Taking the more conservative derate according to 215.2(A)(1) means my conductor ampacity derate needs to be 0.728. Now, because I am using 90°C conductor on a 75°C terminal the derates apply to the 90°C column in 310.15(B)(16). Finally, my interpretation of 110.14(C) says that this wire can only be used so long as the derated conductor ampacity results in a lower ampacity than the 75°C

From 110.14(C)
The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correct, or both.

From 110.14(C)(1)(b)(2)
Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors.

Is this a correct understanding and application of conductor ampacity derates? In a situation where my combined ambient + CCC derate is lower than 0.8, then is it also correct to apply the continuous current derate to the 90°C wire and check that against the 75°C entry?

This portion in RED is incorrect the way you wrote it. If you look at 110.14(c) it says it is PERMITTED to use the higher rated wire insulation ampacity for corrections and 110.14(c)(1)(b) says if the equipment is rated over 100 amps you must use the 75*C column (not 60* in other words if equipment is not labled) and if you want to use a column above that, the equipment must be rated for it (90*C on both sides of the wire). Usually this will be a lug in a junction box rated at 90*C with 90*C wire running to 90*C equipment or lug in a j-box.

If your using 90*C wire, make your corrections off the 90*C column. If this is connecting to 75*C terminations/equipment you would compare that to the 75*C column. Which ever number is lower that is what the wire is rated for. All of your corrections would be off the wire insulation rating. If your wire after making corrections on it is still rated higher than 75*c column that means your wire is OK to use but you cant have an ampacity/load on that circuit higher than the 75*C rating. If your ampacity on the wire using the 90*C column is lower than the 75*c column than that wire would be rated at the lower number (90*C after corrections) and not the 75*C column.

EX: 90*c wire on 75*C equipment
Wire Rating at :
90*C (after corrections): 115 amp
75*C (no corrections): 100 amp
Result: your wire is rated for 100 amp

EX: 90*C wire on 75*C equipment
Wire Rating at :
90*C (after corrections): 120 amp
75*C (no corrections): 130 amp
Result: your wire is rated for 120 amp

"
b) Termination provisions of equipment for circuits
rated over 100 amperes, or marked for conductors larger than
1 AWG, shall be used only for one of the following:
(1) Conductors rated 75°C (167°F)
(2) Conductors with higher temperature ratings, provided
the ampacity of such conductors does not exceed the
75°C (167°F) ampacity of the conductor size used, or up
to their ampacity if the equipment is listed and identified
for use with such conductors
"

 

[Dennis Alwon]

I believe the two of you meant the same thing. I took it to mean the final overcurrent protective device cannot be larger than the 75C column after de-rating

 

[david luchini]

Is this a correct understanding and application of conductor ampacity derates? In a situation where my combined ambient + CCC derate is lower than 0.8, then is it also correct to apply the continuous current derate to the 90°C wire and check that against the 75°C entry?

The continuous current factor applies to the 75C rating, not the 90C rating.

 

[Carultch]

I believe the two of you meant the same thing. I took it to mean the final overcurrent protective device cannot be larger than the 75C column after de-rating

Unless 240.4(B) can apply, making it "protected" by a slightly greater rating of the OCPD.