pv source circuit wire sizing

[wwhitney]

The exception does not specify "or lack thereof where not required". It only refers to 100% continuous duty rated equipment with overcurrent devices.

The phrase "an assembly, together with its overcurrent device(s)" to me covers an assembly with 0 or more OCPD, and is not restricted to assemblies with 1 or more OCPD. At best it is ambiguous. But the physics supports my interpretation, as the 125% factor for continuous loads is only due to OCPD limitations.

Cheers, Wayne

 

[ggunn]

The phrase "an assembly, together with its overcurrent device(s)" to me covers an assembly with 0 or more OCPD, and is not restricted to assemblies with 1 or more OCPD. At best it is ambiguous. But the physics supports my interpretation, as the 125% factor for continuous loads is only due to OCPD limitations.

Cheers, Wayne

This argument is moot. Most people use #10 PV wire for DC source circuits; even the 75 degree ampacity far exceeds what it needs to be.

 

[Zee]

This argument is moot. Most people use #10 PV wire for DC source circuits; even the 75 degree ampacity far exceeds what it needs to be.

Sure, most use #10......and with 10A or less, it is more than adequate. Regardless which algorithm is used, #10 is fine usually.

At the same time, it is fair to say we discuss some of the less obvious situations here.
Including:
1. #12 is used at times (I have seen 9 @ #12 wires in a 1/2" EMT). (so 8 @ CCC's in a raceway is also a major derate factor)
2. Combining two PV strings into one is fairly common..... not to mention three! Now we are talking 20A.... maybe 30A.
3. At times there are significant "# of CCC's in a raceway" derate factors to apply and /or ambient temp. derates..... as much as 50%.
4. We now have PV mods over 10A, and more....soon enough we will need to re-consider whether #10 is enough in some cases, even for a single string.
E.g. opti strings are already at 15A.

 

[ggunn]

Sure, most use #10......and with 10A or less, it is more than adequate. Regardless which algorithm is used, #10 is fine usually.

At the same time, it is fair to say we discuss some of the less obvious situations here.
Including:
1. #12 is used at times (I have seen 9 @ #12 wires in a 1/2" EMT). (so 8 @ CCC's in a raceway is also a major derate factor)
2. Combining two PV strings into one is fairly common..... not to mention three! Now we are talking 20A.... maybe 30A.
3. At times there are significant "# of CCC's in a raceway" derate factors to apply and /or ambient temp. derates..... as much as 50%.
4. We now have PV mods over 10A, and more....soon enough we will need to re-consider whether #10 is enough in some cases, even for a single string.
E.g. opti strings are already at 15A.

Well, OK, but what I use always works. For a given wire size I derate the 90 degree ampacity for conditions of use (ambient temp and conduit fill), I derate the 75 degree ampacity for continuous use (yeah, I know, but X 1.25 is the same as divide by 0.8), and both results have to be > 1.25 X Isc. There may be fringe cases where this is more conservative than it needs to be but it always errs to the side of caution and 95% of the time #10 is plenty big. I do the math and move on.

 

[ggunn]

This is the difference between an exam question and the real world. An exam will ask what the smallest wire is that I can use in a given situation while in the real world the question is whether I can use the buttload of #10 I have in the truck.