De-rate calculations

[Garbluck]

4.25kW system with Enphase Micro-Inverters (M-215) Ontario area

The inspector wants derate calculations in the plans. I've been busting my balls trying to figure this out ): Here's the response.


Everything I find in CEC with 45 celsius just doesn't show up on the tables... I'm so bad

 

[ggunn]

4.25kW system with Enphase Micro-Inverters (M-215) Ontario area

The inspector wants derate calculations in the plans. I've been busting my balls trying to figure this out ): Here's the response.

View attachment 11625
Everything I find in CEC with 45 celsius just doesn't show up on the tables... I'm so bad

NOE: All this is assuming the CEC is the same or very similar to the NEC:

If you have more than three current carrying conductors in a conduit, you have to derate their ampacity, and the table the inspector pointed out shows by how much for how many conductors.

Likewise, the table referenced by the inspector shows by how much 30 degree C ampacity has to be derated for different temperature ranges; find your range on the side of the chart and read across to the conductors you are using.

The rooftop adder is going to be significant for you if your conductors are close to the roof; I never put them below the 3-1/2" breakpoint. See the chart he referenced.

As an example, if you start with conductors rated at 30A at 30 degrees C, and you have 4 CCC's which gives you a derate of 0.8 (from memory; look it up), and the 45 degree C gives you a 0.8 derate ( I dunno; look it up), and your distance off the roof gives you a derate of 0.8 (likewise), then your ampacity is 30A * 0.8 * 0.8 * 0.8, or 15.36A.

The math is simple but all of this stuff should have been considered in the design phase of the project and the conductors sized accordingly. Good luck.