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Bettesworth Construction
building wire

Can You Pull Romex Through Conduit? NM-B, Conductors, and Wet-Location Rules

You should not strip NM-Bโ€™s inner wires and use them as conduit conductors. Location, product markings, fill, ampacity, and local code determine the right wiring method.

By Bettesworth Construction Team 4 min read
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It depends what you mean by โ€œpull Romex through conduit.โ€ The insulated wires inside NM-B cable should not be stripped out and used as individual conduit conductors; Cerrowire says they lack the required markings. Intact NM cable is also not permitted in wet locations such as exterior or underground conduit, according to IAEI guidance. A raceway installation generally calls for individual conductors listed and marked for the routeโ€™s conditions, with local code, fill, and ampacity checked separately.

First, distinguish the two wiring methods

โ€œRomexโ€ is commonly used to mean nonmetallic-sheathed cable. The manufacturer guidance cited here specifically addresses Type NM-B, so it should not be assumed to settle every question about every cable type or installation.

  • Intact NM-B cable: The outer jacket remains around the insulated conductors as the cable is routed.
  • Individual conductors in a raceway: Separate insulated wires are pulled through conduit. Removing the NM-B jacket and using its inner wires this way is a different proposalโ€”and Cerrowire says not to do it.

The answer for a particular route depends on its environment, the productโ€™s listing and markings, fill and ampacity, and the electrical code adopted by the local jurisdiction.

Why you should not strip NM-B conductors for conduit

Cerrowireโ€™s Electrical FAQs answers no to whether NM-Bโ€™s inner insulated conductors can be stripped out and used in conduit. It explains that although the conductors may meet thickness and other applicable requirements associated with THHN wire, they are prohibited from carrying the surface markingsโ€”such as โ€œTHHN,โ€ โ€œ-B,โ€ or an ampacity or temperature ratingโ€”that are required for single conductors pulled into conduit.

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Use individual conductors that are listed and marked for their intended conditions instead. THHN/THWN-2 building wire is a common conductor category to consider for raceways, but the productโ€™s actual markings must establish suitability for the specific route. The cableโ€™s inner wires do not become suitable raceway conductors simply because they fit inside the conduit.

How location changes the answer

Dry indoor route

NM cable is intended for normally dry locations. Whether a particular dry-location use of intact NM-B inside a raceway is permitted depends on the installation details and locally adopted code; the cited sources do not establish a blanket approval or prohibition for every such use. Do not treat a conduit as automatically making an otherwise unsuitable cable acceptable.

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Exterior or underground conduit

IAEIโ€™s 2014 article, โ€œCable Wiring Methods,โ€ says conduits run outside or underground are considered wet locations and that NM cable is not permitted there. A racewayโ€™s interior can be exposed to moisture even when the conduit appears sealed. For such a route, the conductors or cable must be listed for wet-location conditions under the applicable code.

NFPA code-development material for the 2025 NEC cycle likewise addresses wet interiors of raceways in wet locations above grade and calls for wiring installed there to be listed for wet locations. That preliminary report is code-development material, not proof of what your jurisdiction has adopted. Confirm the applicable requirements locally.

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What to check before choosing a wiring method

Permission to use a wiring method, conduit fill, and ampacity are separate checks. A route that appears to have enough physical space may still use an unsuitable wiring product or fail another code requirement.

  1. Identify the cable or conductor. Confirm whether the proposal is intact NM-B or individual conductors, and check the productโ€™s listing and surface markings.
  2. Classify the route. Determine whether the raceway is in a normally dry location or a wet location, including exterior and underground portions.
  3. Verify fill. Check the locally adopted codeโ€™s fill rules for the actual cable or conductor arrangement. NFPA public-comment material for the 2022 NEC cycle points to Chapter 9, Table 1 in discussing cable fill, but that proposal material is not a substitute for adopted code text.
  4. Check ampacity and installation conditions. Conductor ampacity can depend on the wiring method and installation conditions. IAEIโ€™s 2014 discussion includes temperature and ampacity considerations for NM cable; its article is not a current, jurisdiction-specific code determination.
  5. Confirm local requirements. Check the adopted NEC edition and amendments with the authority having jurisdiction (AHJ) or a qualified local electrician before installation.
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Practical decision guide

Proposed approach What the cited guidance establishes What to do
Strip NM-Bโ€™s inner wires and pull them through conduit Cerrowire says no: the inner conductors lack the required surface markings for single conductors pulled into conduit. Use individual conductors listed and marked for the routeโ€™s conditions.
Run intact NM cable through conduit in a dry location The sources do not establish a blanket rule covering every dry-location installation. Check the exact route, installation details, and locally adopted code.
Run NM cable in exterior or underground conduit IAEIโ€™s 2014 guidance identifies these conduits as wet locations where NM cable is not permitted. Choose wiring listed for wet-location conditions and verify local requirements.

For a specific job, a qualified electrician can check the route, conductor markings, fill, ampacity, and local amendments together. Do not rely on a wireโ€™s appearance or fit as evidence that the installation is permitted.

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