Fortunately most 1" trade size conduit is somewhat larger than 1" actual. Now since 12-2NM is 0.40" wide (400 mil), that means 2 in conduit requires 1.016" conduit ID. So if the other cable is Y width, it's literallyĪnd if both wires are the same size W, then minimum I evaluates to 2.54 * W for 2 wires of W width in conduit. Now, this extends for 2 wires in conduit, where only 31% conduit fill is allowed (because of the strong tendency for 2 wires to bind, especially when they are wide cables). That means to be legal, this must be true:Īssuming 1 wire in conduit, the conduit ID must be 138% of the wire width. With 1 wire in a conduit, the one wire can't fill more than 53% of the conduit. OK, so say your conduit is I width in interior cross section. The area of the wire isĪnd our unit is circular inches (or circular mils if we started with mils). Suppose your wire is W inches width in the widest dimension. So a "circular inch" is not a weird unit, and is in fact used in electrical already in the fashion of the KCMil. A circular inch is 1 million CMil or 1000 KCMil. KCMil or MCM mean 1000 of those circular mil units. So a circular mil means the area of a circle 1/1000" across. Mil or M means "Mil", or 1/1000 (of an inch).C means circular area, instead of square area.When you get into large wires, the copper dimension starts to be expressed in a unit called K C Mil, or M C M. Get pi out of the picture: Think in circular inches For two 12/2 UF, you'll need at least 1-1/4" conduit. I can't imagine how it was ever accomplished! It carries no more current than 4x THHN wires, which go effortlessly through 3/4" EMT.įor two 12/2 NM cable, you need at least 1" conduit (by calculations below) but it'll still be a difficult pull. I just tore the conduit out wires and all I cannot get the NM out of the conduit, it's in there so tight. I just recently tore out an installation where someone chicken-choked two 12/3 NM into a 3/4" EMT conduit. This is just for exposure protection and I am not clear what the best practices are. I know I shouldn't put cable in conduit for the full run, which I am not doing. Would this be acceptable to pull two 12-2 cable per 3/4" conduit at least for the first 2 outlets or do I need to put in a junction box along the way and then just run a 1/2" down to the outlet? I'd really prefer not to do this. It isn't a wet or damp location, I just want it protected from any possible accidents. I would prefer to not have to run multiple conduits per box and was hoping I could use 3/4" LT or PVC - again just for the vertical section from the attic to the outlet. I would like to run this exposed section, about a 10 ft vertical run per outlet, in conduit. The run would be via the attic and the cable would just be exposed on the vertical run from the attic down to the outlet. I would like to go from the panel to the first outlet, then to the second and then the 3rd. I am putting in a few new outlets in an enclosed patio, running a new circuit through the attic using 12-2.
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