NEC Tables · Conduit Fill · Chapter 9

NEC conduit fill table

How many wires fit in the pipe — every trade size, every common conduit type, with the 40% rule math shown instead of hand-waved.

Free · NEC 2023 · Updated
21 conductors
3/4 · 14 AWG
maximum THHN/THWN-2 conductors at 40% fill (3+ wires)
Exam trapThe 40% limit applies at 3 or more conductors. Two conductors get only 31%, one gets 53% — and conduit nipples under 24 in. are allowed 60%. Chapter 9, Note 4 is where the exam hides this.

These maximum-conductor counts are computed from the NEC the way the code intends: each conduit’s usable 40% area (Chapter 9, Table 4) divided by the wire’s cross-section (Table 5). That is exactly how Annex C is built — and how you verify a count when the inspector asks. Counts shown are THHN/THWN-2; mixed wire sizes need the calculator.

EMT

Trade size14 AWG12 AWG10 AWG8 AWG6 AWG4 AWG3 AWG2 AWG1 AWG1/0 AWG2/0 AWG3/0 AWG4/0 AWG
1/212953211100000
3/42116105422111000
13526169643221111
114614428161176533221
112836138221698754332
213810063362616131187654
212241176111644628242015121087
336426616796694236302219151310
312476347218126915647392924201714
46084432791611167160503731262218
58336073832201599883695143363024
612028765523182301411191007462524336

PVC Sch 40

Trade size14 AWG12 AWG10 AWG8 AWG6 AWG4 AWG3 AWG2 AWG1 AWG1/0 AWG2/0 AWG3/0 AWG4/0 AWG
1/211853211000000
3/4201595422111000
13425159643221111
114594327151175533221
112815937211598654322
21359862352515131187544
2121931418951372219161210875
32992181377957352925181513108
312401292184106764740332420171412
4517377238137996051433227221815
58145943742151559581685042352924
61178859541312225138117987361514235

PVC Sch 80

Trade size14 AWG12 AWG10 AWG8 AWG6 AWG4 AWG3 AWG2 AWG1 AWG1/0 AWG2/0 AWG3/0 AWG4/0 AWG
1/28642110000000
3/4161274311110000
12820137532211110
11451372313965432211
112705132181387543322
2118865431221311976543
212169123784532191614108765
3265193122705031262216131197
31235826116494684235302218151210
4464338213123885446382824201613
57365363381951408673614538322622
61055769485279201124105886555463831

RMC

Trade size14 AWG12 AWG10 AWG8 AWG6 AWG4 AWG3 AWG2 AWG1 AWG1/0 AWG2/0 AWG3/0 AWG4/0 AWG
1/212953211100000
3/42216106422111000
13626169743321111
114624528161276533221
1128562392216108754332
214010264372616141187654
2122001469253382320161210876
33092251428159363025191613119
312412301189109784841342521181412
45313872441401016252443227231915
58336073832201599883695143363024
612028765523182301411191007462524336

IMC

Trade size14 AWG12 AWG10 AWG8 AWG6 AWG4 AWG3 AWG2 AWG1 AWG1/0 AWG2/0 AWG3/0 AWG4/0 AWG
1/2141063211100000
3/42417116422211100
139281810743322111
114674931181276543222
1129166422417109754432
214910968392817141297654
2122111549756402421171311976
33262381508662383227201714119
312436318200115835143362722191513
45624092581481076656473429242016
587964140423316810387735445383126
612689255833362421491261067866554538

FMC

Trade size14 AWG12 AWG10 AWG8 AWG6 AWG4 AWG3 AWG2 AWG1 AWG1/0 AWG2/0 AWG3/0 AWG4/0 AWG
3/84321000000000
1/213963211100000
3/42116105422111000
13324158633221111
114523824131065432211
112765535201497644322
21349861352515131187544
2122021479353382320161210876
32912121337755342924181512108
312396289182105754639332420171411
4518377238137996151433227221815

Values derived from the 2023 National Electrical Code for exam study. Verify installations against the adopted code and local amendments.

Race your codebook — 3 lookups on this table

Q1

A restricted industrial establishment has a Class I, Division 1 area classified that way solely because of inadequate ventilation. The owner wants to install a gas detection system so the area can instead use equipment and wiring methods suitable for Class I, Division 2. Which section permits this reclassification and sets the alarm threshold?

  1. A 500.7(K)(4)
  2. B 500.7(K)(3)
  3. C 500.7(K)(2)
  4. D 500.7(D)
Show answer & explanation

Correct: C — 500.7(K)(2)

500.7(K)(2) covers the specific case of a location classified Division 1 due to inadequate ventilation, allowing Division 2 methods when a gas detection system alarms at 40 percent LFL. 500.7(K)(3) instead addresses an enclosed building/space adjoining a Division 2 area being derated to unclassified, and 500.7(D) is the unrelated purged-and-pressurized protection technique.

Q2

An electrician is installing gas sensors inside a control panel that houses instrumentation measuring flammable process gas, intending to rely on the detection system so the panel's electrical equipment can be treated as suitable for Class I, Division 2. Which section governs this specific application and its alarm setpoint?

  1. A 500.7(K)(3)
  2. B 500.7(K)(1)
  3. C 500.7(K)(4)
  4. D 500.7(K)(2)
Show answer & explanation

Correct: C — 500.7(K)(4)

500.7(K)(4) specifically addresses the interior of a control panel with flammable-gas instrumentation, setting the alarm at 40 percent LFL. 500.7(K)(2) applies to areas classified Division 1 from poor ventilation, 500.7(K)(3) to enclosed buildings/spaces, and 500.7(K)(1) only lists the general equipment and documentation requirements common to all uses of this technique.

Q3

An installer is selecting a protection method for equipment being installed in a Class I, Division 1 hazardous location and wants the full list of acceptable protection techniques along with which ones are suitable for that specific classification. Which section lists all the recognized protection techniques and points to the table showing their suitability by location?

  1. A 500.7
  2. B 500.6
  3. C 500.7(A)
  4. D 500.6(A)
Show answer & explanation

Correct: A — 500.7

500.7 is the parent section that lists protection techniques (A) through (P) and references Chapter 9, Table 13 for suitability by location, while 500.6 and 500.6(A) instead cover equipment marking/material group classifications, not protection techniques.

Keep going

Conduit Fill Calculator Mixed wire types & sizes Table 9.4 — conduit dimensions The areas behind these counts Conduit Types NEC guide
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