How Many Low Voltage Wires Fit in 1/2 Inch Liquidtight?
A user asked the app how many low voltage wires can go in 1/2 inch liquidtight. There is no single count printed in the Code for this one, because low voltage cables come in many diameters. What the NEC gives you is the fill method, and once you know your cable diameter the answer takes one minute of math.
The 40 percent rule
Chapter 9 Table 1 of NEC 2023 limits a raceway with three or more wires to 40 percent of its internal cross sectional area, and Note 9 tells you to treat a multiconductor cable as a single conductor using its actual diameter. Table 4 lists 1/2 inch liquidtight flexible nonmetallic conduit type B with a total internal area of about 0.314 square inches, which puts the 40 percent allowance at roughly 0.125 square inches. Liquidtight flexible metal conduit in 1/2 inch is nearly identical. So the working number to remember is 0.125 square inches of cable in a 1/2 inch liquidtight run.
Now apply it to real cables. An 18/2 thermostat or bell wire around 0.15 inches in diameter has an area of about 0.018 square inches, so six to seven of them fit. A Cat6 cable at 0.24 inches diameter is about 0.045 square inches, so two fit and a third busts the limit. An 18/5 sprinkler or thermostat cable near 0.20 inches diameter comes in around 0.031 square inches, allowing four. Cable diameter is printed on the box or spec sheet; measure with calipers if in doubt, and calculate area as diameter squared times 0.7854.
Does the fill rule even apply to Class 2?
Fair question, since Article 725 relaxes many Chapter 3 rules for Class 2 and Class 3 circuits. When you choose to install those cables in a raceway, the raceway fill limits of 300.17 and Chapter 9 still apply to keep pulls from damaging insulation, and inspectors enforce it that way. Heat is rarely the issue at Class 2 power levels; jam and pull damage are. Also keep Class 2 conductors out of raceways that carry power conductors unless one of the 725.136 exceptions applies, such as a barrier or the power circuit being there solely to supply the connected equipment.
Practical advice from the field: liquidtight has more friction than EMT, so staying near half of the allowed fill makes long pulls and future additions painless.