Old age is messin' with me (again). I can't get my brain to comprehend Note (7) to Chapter 9 Tables.
Can someone translate this.
Specifically I was working on a teaching assignment where my conduit nipple fill allows 163.75 #12s (2.178 conduit area/0.0133 wire area).
In the real world this would make no difference but in the academic world with Note 7, would I be allowed 164 wires or 163 ?
In the academic world, you have to round down on conduit fill calculations.
In the real world, you have to do so as well.
I'm guessing that this is 2" IMC, with wire type THWN-2? That is the closest my conduit sizer got, to the 60% fill limit for nipples. I also don't recommend depending on the 60% nipple fill limit, unless you really have to, because it takes skill to fit that wire through. In fact, with two wires it is impossible to fill higher than 50%, but two wires in a nipple is a blindspot of the code.
Another point: the diameters given for the common wire types are upper limits of what can be manufactured, and meet the industry standard for that kind of wire. If you have control over what manufacturer supplies the wire, you can use the nominal OD values from the datasheet, instead of the values in the chapter 9 tables. I don't recommend doing this, because it is rare that the person making the plan set has precise control of wire selection.
This can happen in my trade with PV wire, which doesn't have an NEC standard diameter table yet. I have to specify on the drawing set "PV Wire refers to Encore products. Cross check all conduit fill calculations, if a different manufacturer will be procured." And Encore PV wire is the most common in my area anyway, so it usually isn't a problem.
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