210.19 (A) 1 Exception #2

[xformer]

Hello,
Can someone give a practical example for 210.19 (A) 1 Exception #2? I am looking for a way to explain the situation better.

 

[augie47]

Which Code cycle.. don't see such in '14 or '17

 

[Dennis Alwon]

It is in the 2020

210.19(A)(1) General. Branch-circuit conductors shall have an ampacity not less than the larger of 210.19(A)(1)(a) or (A)(1)(b) and comply with 110.14(C) for equipment terminations. (a)Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size shall have an ampacity not less than the noncontinuous load plus 125 percent of the continuous load in accordance with 310.14. (b)The minimum branch-circuit conductor size shall have an ampacity not less than the maximum load to be served after the application of any adjustment or correction factors in accordance with 310.15.

Exception No. 1 to (1)(a): If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampacity of the branch-circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load in accordance with 110.14(C).

Exception No. 2 to (1)(a) and (1)(b): Where a portion of a branch circuit is connected at both its supply and load ends to separately instal⁠led pressure connections as covered in 110.14(C)(2), it shall be permitted to have an allowable ampacity, in accordance with 310.15, not less than the sum of the continuous load plus the noncontinuous load. No portion of a branch circuit installed under this exception shall extend into an enclosure containing either the branch-circuit supply or the branch-circuit load terminations.

 

[don_resqcapt19]

I believe it was in the 2017 code only for feeders and the 2020 code expanded it to branch circuits.

Lets say the load for the branch circuit is 350 amps. For a normal installation, you would install 500 kcmil with a 75°C ampacity for this circuit. Using the exception, you would install 500 kcmil from the breaker to power distribution block in an junction box.. You would install 350kcmil, from the power distribution block to a second junction box at the load end, and then install 500 kcmil from that connection point to the load.
In my opinion, there is no practical use for this exception, unless maybe you pulled in the wrong size conductor on the original install. To do this in a new install, you are adding a lot of labor, and additional points of failure. I guess if the run is long enough, it may be cost effective to use this exception.

If I am the one paying the power bill, this exception will not be used and I will be paying for the additional I²R losses for the life of the installation. If the circuit is heavily loaded and running most of the time, the extra costs on my power bill would pay for the normal sized conductors within a few years.

 

[xformer]

I am not understanding why they would allow the central part of the circuit to run a lil hotter than the front and back sides.

 

[don_resqcapt19]

I am not understanding why they would allow the central part of the circuit to run a lil hotter than the front and back sides.

Because the only reason we can't normally use 90°C ampacities is the temperature rating of the equipment at both ends of th circuit.