Guide · Conduit & connectors
Liquid-tight conduit fill chart: how many THHN conductors fit in LFNC-B
Conduit fill is a simple area calculation, but the LFNC-B numbers are different from EMT and PVC because the internal diameter is different. Here are the internal areas, the 40% fill limit and a ready-reckoner for THHN/THWN conductors.
The rule
NEC Chapter 9, Table 1 allows a raceway to be filled to 53% of its internal area with one conductor, 31% with two conductors, and 40% with three or more. The internal area of each LFNC-B trade size comes from Chapter 9, Table 4 (Article 356 section); conductor areas come from Table 5. Note 4 to Table 1 also allows the next-higher whole number of conductors when the calculation lands at 0.8 or more.
LFNC-B internal area and 40% fill
Trade size |
Total internal area (in²) |
40% fill (3+ wires) |
31% fill (2 wires) |
53% fill (1 wire) |
|---|---|---|---|---|
3/8″ |
0.192 |
0.077 |
0.059 |
0.102 |
1/2″ |
0.314 |
0.125 |
0.097 |
0.166 |
3/4″ |
0.541 |
0.216 |
0.168 |
0.287 |
1″ |
0.873 |
0.349 |
0.270 |
0.462 |
1-1/4″ |
1.528 |
0.611 |
0.474 |
0.810 |
1-1/2″ |
1.981 |
0.792 |
0.614 |
1.050 |
2″ |
3.246 |
1.298 |
1.006 |
1.720 |
Maximum THHN / THWN / THWN-2 conductors (all the same size)
Conductor |
Area (in²) |
3/8″ |
1/2″ |
3/4″ |
1″ |
1-1/4″ |
1-1/2″ |
2″ |
|---|---|---|---|---|---|---|---|---|
14 AWG |
0.0097 |
8 |
13 |
22 |
36 |
63 |
81 |
134 |
12 AWG |
0.0133 |
5 |
9 |
16 |
26 |
46 |
59 |
97 |
10 AWG |
0.0211 |
3 |
6 |
10 |
16 |
29 |
37 |
61 |
8 AWG |
0.0366 |
1 |
3 |
6 |
9 |
16 |
21 |
35 |
6 AWG |
0.0507 |
1 |
1 |
4 |
7 |
12 |
15 |
25 |
4 AWG |
0.0824 |
1 |
1 |
2 |
4 |
7 |
9 |
15 |
3 AWG |
0.0973 |
1 |
1 |
1 |
3 |
6 |
8 |
13 |
2 AWG |
0.1158 |
— |
1 |
1 |
3 |
5 |
7 |
11 |
1 AWG |
0.1562 |
— |
1 |
1 |
1 |
4 |
5 |
8 |
Worked example: pool pump
A 240-volt pool pump on a 20-amp circuit needs two 12 AWG hots and a 12 AWG equipment grounding conductor: three conductors × 0.0133 in² = 0.0399 in². The 40% limit for 1/2″ LFNC-B is 0.125 in², so 1/2″ liquid-tight is fine, with plenty of room to add a second pump circuit later. In practice many installers choose 3/4″ for pulling ease and future capacity.
Worked example: 3-ton condenser
A condensing unit on a 40-amp circuit with 8 AWG copper: two 8 AWG hots plus a 10 AWG ground = 2 × 0.0366 + 0.0211 = 0.0943 in². That is under the 1/2″ limit of 0.125 in², so 1/2″ works on paper, but a 3/4″ whip is the usual choice: the disconnect knockouts are typically 3/4″ and the pull is easier.
Other things that limit fill
- Derating. More than three current-carrying conductors in a raceway triggers ampacity adjustment (310.15(C)). Fill may allow 9 wires; the ampacity table may not.
- Pull length and bends. LFNC is limited to 360° of bends between pull points; long runs with many wires pull hard through flexible conduit.
- Connector throat. The liquid-tight connector’s inside diameter is smaller than the conduit; check that the bundle passes the fitting.
Parts
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