Kyle J
Member
- Location
- Southern Utah
As I'm preparing for the upcoming NABCEP exam, I'm trying to figure out the correct calculation to determine ampacity of the inverter output circuit.
See Mike Holt's book, "Understanding NEC requirements for Solar Photovoltaic Systems", pg. 348 Figure 690-43 and pg. 350 Figure 690-48.
Mike has a reference for Figure 690-43 ampacity: *690.8(A)(3) which states, "(3) Inverter Output Circuit Current. The maximumcurrent shall be the inverter continuous output currentrating. "
However, in Mike's example he is taking the inverter continuous output nameplate rating x 1.25.
690.8(B) states, "Circuit conductors shall be sized to carry not less than the larger of 690.8(B)(1) or (2)."
(B)(1) states to add 125% to max currents in 690.8(A)
As I read the NEC, I believe the calculation to add 125% to inverter output (in the above examples, 24A) is correct.
However, Mike appears to reference 690.8(A)(3) on both pages, but does not add 125% to the example on pg. 350. Is Mike's reference incorrect? Should the reference be 690.8(B)(1)?
Thanks for all who read & reply to this, either way in the book's examples the conductor size is OK for the calculated current but I'm wondering, "What if…?" in the NABCEP exam there is a question similar that has some tighter ampacity calculations. Do I use (A)(3) or the higher of (B)(1) or (2)?
See Mike Holt's book, "Understanding NEC requirements for Solar Photovoltaic Systems", pg. 348 Figure 690-43 and pg. 350 Figure 690-48.
Mike has a reference for Figure 690-43 ampacity: *690.8(A)(3) which states, "(3) Inverter Output Circuit Current. The maximumcurrent shall be the inverter continuous output currentrating. "
However, in Mike's example he is taking the inverter continuous output nameplate rating x 1.25.
690.8(B) states, "Circuit conductors shall be sized to carry not less than the larger of 690.8(B)(1) or (2)."
(B)(1) states to add 125% to max currents in 690.8(A)
As I read the NEC, I believe the calculation to add 125% to inverter output (in the above examples, 24A) is correct.
However, Mike appears to reference 690.8(A)(3) on both pages, but does not add 125% to the example on pg. 350. Is Mike's reference incorrect? Should the reference be 690.8(B)(1)?
Thanks for all who read & reply to this, either way in the book's examples the conductor size is OK for the calculated current but I'm wondering, "What if…?" in the NABCEP exam there is a question similar that has some tighter ampacity calculations. Do I use (A)(3) or the higher of (B)(1) or (2)?