How many 14/2 romex cables can I, according to NEC (or safely), put in a 1/2 pvc conduit? For background: the conduit will be buried until surfacing in a junction box; using burial-rated "romex"black but want the additional security of conduit.
Use individual THWNs here instead, or else prepare to face the full wrath of the fill rules (and the electrician that comes over to rescue your pull job!)
A 1/2" schedule 80 PVC conduit has 56mm2 of usable fill for individual wires, or 75mm2 of usable fill for a single wire or cable. A 14AWG THWN takes up about 6.3mm2 of fill; however, a multiconductor cable's fill is computed as if it were a round wire with a diameter equal to the major diameter (long dimension) of the cable (Note 9 from chapter 9 of the NEC):
(9) A multiconductor cable, optical fiber cable, or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.
As a result of this, given that a 14/2 UF cable has dimensions of 0.185" by 0.385", as per Encore Wire's specsheet, or 4.7mm by 9.8mm in handier units, we then get an effective fill area for a single 14/2 UF cable of just over 75mm2!
Given that a single 14AWG bare copper conductor for the EGC counts for 2.1mm2 of fill, you can get 4 hots and 4 neutrals (i.e. 4 circuits) + 1 EGC (which all 4 circuits can share) into your conduit without busting the 56mm2 fill limit and allowing the conductors to carry their full permitted 15A still due to the way the derate rules work. Compare that to the 75mm2 UF cable not quite fitting down the conduit by Code, making you emit profanity all the way through the pull, while only providing a single circuit to wherever this is going.
(Of course, this conduit will let you run a bigger feeder there if you want multiple circuits at the destination, too -- you could get 3 10AWG THWNs + a bare 10AWG ground down there and power your 4 15A circuits from a subpanel that way, instead of stuffing more 14AWG wires down the conduit.)
At the first junction box at the start of the conduit, you terminate the Romex cable. When there are several things of different colors, that is cable. Individual things are wire.
Through the conduit, you run special stuff called THWN. This is not a cable. This is sold as individual wires and you need 3: black white and green or bare. They make this in solid or stranded, I recommend stranded. These will go very easily down the conduit. You will not believe how flexible it is. You cannot make THWN by tearing the jacket off Romex.
Use wirenuts to attach each color to the corresponding romex wire.
At the other end of the conduit, do the same thing to transition back to Romex for your last bit of distance.
Code requires you fully assemble the conduit before pulling wires through it. You can't lay the wire out and slide sticks of conduit over it. That's why Romex is almost impossible to pull.