The homeowner's question

Open an attic hatch in Greater New Orleans and you will see several kinds of wire doing several kinds of jobs — yellow cable stapled along joists, gray cable heading out toward a shed, metal-armored cable disappearing into a panel, single wires inside conduit on an outside wall. Are those the right wires in the right places, or is somebody's shortcut waiting to fail?

The short answer

Every wire type pairs a conductor with insulation matched to a location; cables add an outer jacket. Inside dry walls, the standard is Romex — the yellow- or white-sheathed cable. Its real name is NM-B (nonmetallic-sheathed, type B); Romex is Southwire's brand name that became the word everybody uses. Where the location is wet or damp — underground, in a slab in direct contact with the earth, in pool-equipment locations Article 680 treats as wet — the wire needs a wet-location rating: UF-B cable, THWN-2 conductors inside conduit, or metal-clad cable listed for wet locations. A roofed carport or porch may be damp if it is protected from beating rain and runoff; classify the actual location by its exposure — conductors listed for damp locations are the minimum there, and Romex is barred from damp locations too. Under a house, check with your parish or city AHJ first — some local jurisdictions treat crawlspaces as damp locations and do not permit NM-B there. MC not listed for wet locations, and Romex anywhere damp or wet, are the wrong wire in the wrong place.

What you are seeing

A few sights from real service calls around here. In the attic, Romex (NM-B) runs stapled along joists — normal, as long as it stays dry and protected from damage. Under the house, check with your parish or city AHJ — some local jurisdictions treat crawlspaces as damp and do not permit NM-B there. Outside, a gray cable buried to a detached shed or an outdoor receptacle — that wiring method must be listed for the installation, such as UF-B or wet-rated conductors in a suitable raceway. Low-voltage landscape lighting uses a cable listed for that system. On an exterior wall, conduit with single conductors inside — if that conduit sits in a wet location, exposed to weather, the conductors inside should carry a \"W\" in their rating, because the inside of a raceway in a wet location counts as a wet location. Under cover, conductors listed for damp locations are the minimum, and the raceway, boxes, and fittings must also be suitable for the location. And in older homes, cloth-wrapped or steel-armored cable from a previous era — yesterday's guide to old wiring in New Orleans homes covers what an inspection finds in those systems.

What is actually happening

The National Electrical Code (NEC) draws its lines around water. A \"wet location\" in Code terms covers installations underground or in concrete slabs and masonry in direct contact with the earth, places subject to saturation with water, and unprotected locations exposed to weather. The rule that surprises homeowners: the interior of a raceway — conduit or another enclosed channel — in a wet location is itself a wet location. Conduit is not a raincoat. A conductor inside a conduit in a wet location has to be rated for wet locations on its own merits, conduit or not. A \"damp location\" is the middle case — protected from weather but subject to moderate moisture, like a covered porch or a crawlspace. Conductors listed for damp locations are the minimum there; in practice that usually means individual wet/damp-rated conductors in raceway, UF-B where appropriate, or another listed wiring method.

NM-B — Romex — (NEC Article 334) is permitted only in dry locations in the homes this article is about — not wet or damp ones. NM-B can often be run through an exterior wood-framed wall cavity to feed an outdoor receptacle or light; the cable location is dry, while the exterior box, device, and cover must be rated for their exposure. Type AC armored cable (Article 320) is dry-location only as well: no damp or wet locations, no corrosive conditions, no places subject to physical damage. \"BX\" commonly means Type AC — dry-location cable — not a generic term for all armored cable. Older \"BX\" may be AC or, in some regions, colloquially MC; identification should come from the markings on the cable, not the nickname. Type MC metal-clad cable (Article 330) may be suitable for wet locations only when listed or identified for that use. Two common compliant approaches: MC with wet-rated conductors inside, or MC listed with moisture-impervious construction or jacketing. Two further limits apply separately: direct burial or concrete encasement requires cable identified for that application, and NEC 330.12 bars MC where exposed to destructive corrosive conditions — cinder fills, strong chlorides, caustic alkalis, or chlorine/hydrochloric-acid vapors — unless the sheath/armor itself is resistant or protected by resistant material.

THHN, the single-conductor wire most electricians pull through conduit, carries its own trap. Plain THHN is rated for dry and damp locations at 90°C — not wet locations. The wet-location members of the family are THWN (75°C) and THWN-2 (90°C in dry, damp, and wet locations). THHN sold today is commonly dual-marked THHN/THWN-2 — but the marking on the wire is what counts, not the habit of calling everything in the conduit \"THHN.\" UF-B (Article 340) is the cable built for the wet side: permitted underground including direct burial, and in wet, dry, or corrosive locations. UF-B conductors carry 90°C insulation (340.112), but NEC 340.80 limits UF-B ampacity — how much current the wire can safely carry — to that of 60°C conductors. The lower number governs. Do not size a UF-B run from the 90°C column. (CerroWire's CerroMax UF-B sheet states the same split.)

Two more members of the cast, briefly. The cable running down the mast into your meter is often service-entrance (SE) cable (Article 338) — listed for service conductors, and also permitted as branch circuits or feeders under 338.10(B) when installed per that section. The mast run carries service conductors. It is not a homeowner add-on point; any splice or tap must comply with the service-conductor rules and be handled by a qualified electrician. Do not treat the mast or meter equipment as a convenient splice point. The conduit itself comes in flavors — rigid PVC (352), EMT (358 — not where subject to severe physical damage), rigid metal (344), flexible metal conduit, \"Greenfield\" in trade slang (348), liquidtight \"seal tite\" (350) — each matched to its own exposure and damage risk. The point now is that raceway and conductor are chosen together, for the same location. Pool equipment carries its own additional rules under NEC Article 680 — a wet rating is the starting point there, not the whole rule.

Low-voltage wiring gets a brief word here. Doorbell wire, A/C and thermostat wire, security and shielded wire are listed for low-voltage, power-limited circuits — commonly 24 VAC or less in homes, though Class 2 circuits may operate at up to 30 V RMS AC or 60 V DC. They are not substitutes for 120/240-volt branch-circuit wiring: a cable's printed voltage rating alone does not make it an approved wiring method for a line-voltage circuit — follow its listing and the applicable Code requirements, and using low-voltage cable for a line-voltage circuit is a fire and shock hazard. That is why a single piece of equipment can have both kinds of wiring running to it — line-voltage cable feeding the power, low-voltage cable carrying the control signal from a transformer on that equipment's circuit — each doing its own job. Ethernet and coax carry signals and may carry limited power in listed systems — Ethernet can carry PoE power. Fiber carries light, not electricity (hybrid fiber cable with separate copper conductors is the exception). None of them is general-purpose branch-circuit wiring.

Local note — Greater New Orleans: Some local AHJs treat crawlspaces as damp locations and do not permit NM-B there. This is a local enforcement position or amendment issue, not a blanket national NEC prohibition. Confirm the requirement with the parish or city electrical inspector before opening up or replacing under-floor wiring.

What a professional checks

When an electrician opens up a wiring question in a Greater New Orleans home, the sequence runs like this:

\nRead the jacket. The print on the cable or conductor names the type — NM-B (Romex), UF-B, MC, AC, THHN/THWN-2 — and its rating. If the print is gone or unreadable, check the tag, reel, or carton and the listing information — an unreadable marking is a reason to investigate, not automatic proof of a violation.
\nMatch the wire to the location. Dry interior wall: NM-B is at home. Under the house, check with your parish or city AHJ — some local jurisdictions treat crawlspaces as damp and do not permit NM-B there. Underground, slab in direct contact with the earth, saturation-prone spots, pool-equipment locations Article 680 treats as wet: the wire needs a wet-location rating. A conduit run in a wet location gets wet-rated conductors, because the inside of a raceway in a wet location is a wet location. A roofed carport or porch may be damp if it is protected from beating rain and runoff — classify the actual location by its exposure; conductors listed for damp locations are the minimum there, and NM-B is barred from damp locations too. And check that low-voltage cable is only on low-voltage circuits — doorbell, thermostat, and security cable is not an approved wiring method for a line-voltage circuit.
\nCheck the armored cable. AC (often called BX) belongs in dry locations only. MC in a wet spot needs its corrosion-resistant outer jacket — bare interlocked armor in a wet location is the wrong wire. In a crawlspace classified as damp, check the listing, the conductors inside, the fittings, and corrosion — and let the authority having jurisdiction (AHJ) call it. Modern AC carries a bonding strip that, together with the armor, serves as the ground path; some older armored cable lacks a bonding strip, and its armor may not provide a reliable equipment-grounding path.
\nCheck the terminations and the conduit. Fittings, boxes, and conduit bodies in wet locations need to be rated and intact.
\nLook for the flood line. Cable listed for dry locations that has been under floodwater should be replaced — NEMA's water-damage guidance calls for replacement of dry-location wire and cable after water exposure. Wet-location cable may be evaluated for reconditioning if its ends were not exposed to water and it is not damaged, but that is a qualified person's judgment call, made with the manufacturer's guidance, not a homeowner's.
\nTrace the symptom. A breaker that keeps tripping on a circuit with the wrong wire in a wet place needs investigation — the trip pattern alone cannot prove the cause, and moisture-exposed wiring should be evaluated before parts are replaced. Our guide to why breakers trip walks through reading the trip pattern — instant, delayed, or random — before anyone swaps parts.

The safety, code, and repair boundary

Homeowners can safely read jacket markings on exposed cable and note where each run goes — useful information to hand your electrician. Read from a safe position; do not walk joists or disturb insulation to reach a cable. Do not open the panel, pull devices, or cut into cable to find out more. New circuits, rewiring, and anything involving service-entrance cable, aluminum branch wiring, or flood-damaged cable belong to a licensed, experienced electrician, and whether it needs a permit and inspection depends on the work and your parish or city AHJ. Louisiana adopted the 2020 NEC statewide effective January 1, 2023; your local AHJ has the final word where local amendments apply.

One more: if the wire in question is aluminum branch wiring, do not touch it. Do not attempt pigtail repairs with ordinary wire nuts; use only listed aluminum-to-copper connection methods and have the work evaluated by a qualified electrician.

What to ask the contractor

\"What type is this cable, and is it rated for this location?\"
\"Is this run in a wet location by Code definition — and is the conductor inside rated for it?\"
\"This MC run is in a damp spot — is it listed for this location, and are the conductors inside and the fittings holding up against corrosion?\"
\"What does the flood line mean for this cable — replace or recondition, and who makes that call?\"
\"If you pull a new run here, what type are you pulling, and will it need a permit and inspection?\"

Learn from a Pro — free homeowner guides at abestpros.com/learn-from-a-pro, no ads, no paywall.

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Which Wire Goes Where in Louisiana Homes?

The types and uses of wires commonly used in Louisiana’s homes.

Understanding how wire choices make a difference

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