CON-4 — Cable Assemblies and Flexible Cords
Key Takeaways
- Cable abbreviations identify different listed assemblies: NM, UF, AC, MC, SE, and USE have distinct dry/wet, underground, physical-damage, grounding, and interior-use boundaries.
- Type NM is generally a dry-location method, while Type UF can be identified for direct burial and wet locations; neither listing eliminates required physical protection.
- Type AC uses its armor and internal bonding strip as a recognized grounding path, while Type MC grounding depends on the particular listed construction and often uses an included equipment grounding conductor.
- Flexible cord is permitted for portability, movement, vibration, pendants, and specified equipment connections, but 400.8 generally prohibits using it as concealed or fixed building wiring.
Exam checkpoints
| Checkpoint | What to verify |
|---|---|
| 1 | Cable abbreviations identify different listed assemblies: NM, UF, AC, MC, SE, and USE have distinct dry/wet, underground, physical-damage, grounding, and interior-use boundaries. |
| 2 | Type NM is generally a dry-location method, while Type UF can be identified for direct burial and wet locations; neither listing eliminates required physical protection. |
| 3 | Type AC uses its armor and internal bonding strip as a recognized grounding path, while Type MC grounding depends on the particular listed construction and often uses an included equipment grounding conductor. |
Read the complete cable marking
A cable assembly is a listed wiring method, not just several insulated conductors under a jacket. Identify the exact type, conductor insulation, equipment-grounding construction, voltage and temperature markings, sunlight resistance, direct-burial marking, and any use limitations before applying its article. A raceway sleeve can protect a cable from damage, but it does not convert a dry-location cable into a wet-location cable.
Type NM cable under Article 334 is widely used for concealed dwelling wiring and other permitted dry-location work. Ordinary Type NM and NMS are not permitted in wet or damp locations, in corrosive conditions, embedded in poured cement or concrete, or where exposed to physical damage. Type NMC has a corrosion-resistant, moisture-impervious jacket and broader damp or corrosive uses, but the actual marking and 334.10/334.12 still control. An exterior raceway and an underground raceway are wet inside, so ordinary NM cable is not made acceptable there merely by pulling it through conduit.
Type UF cable under Article 340 can be used in wet locations and, where identified, for direct burial. It can also be used in many places where NM is permitted. Direct-burial permission does not mean the exposed cable can emerge from grade without protection, cross a driveway at any depth, or be installed where subject to physical damage. Apply the cover and emerging-from-grade protection rules in 300.5 and preserve the cable jacket at fittings and bends.
Distinguish AC from MC
Type AC cable under Article 320 has insulated conductors in flexible interlocked metal armor and includes an internal bonding strip in intimate contact with the armor. The qualifying armor-plus-bonding-strip path is recognized as an equipment grounding conductor by 250.118. Type AC is ordinarily a dry-location method and is prohibited in wet locations, where subject to physical damage, and in destructive corrosive conditions. At cut ends, install the required bushing or equivalent protection between conductors and armor and use fittings listed for Type AC.
Type MC cable under Article 330 is a broader family. Depending on its listed construction, it can be used indoors or outdoors, exposed or concealed, in cable tray, in specified hazardous locations, in wet locations, or for direct burial. Those permissions are conditional: the cable must be identified for the environment and its jacket, metallic sheath, conductors, and fittings must satisfy the applicable rule. MC cable is prohibited where subject to physical damage and where the environment will damage an unprotected sheath.
Do not assume every MC armor is the fault-current path. Many MC assemblies contain a full-size insulated or bare equipment grounding conductor. Certain listed MC constructions qualify through a sheath or armor-and-bonding-conductor combination under 250.118. Inspect the marking and listing; do not copy the Type AC bonding-strip rule onto ordinary MC cable. Also do not add an AC-style anti-short bushing to an MC termination as a universal NEC rule—follow the MC fitting listing and manufacturer instructions.
Separate SE from USE
Article 338 distinguishes Type SE cable from Type USE cable. Type SE is intended for aboveground service-entrance use and can be used for permitted feeders and branch circuits under 338.10(B). Where used as interior feeder or branch-circuit wiring, all conductors must be insulated, subject to the limited existing range-and-dryer provision referenced by the rule. Type SE is not permitted underground, with or without a raceway.
Type USE is identified for underground service use and can be direct buried. It is generally not permitted for interior wiring or aboveground use except for allowed termination portions. Some products carry additional conductor or cable listings that permit other uses, but the letters USE alone do not grant an interior feeder raceway use. Read every marking rather than treating SE and USE as interchangeable.
Support and bend the assembly
Type NM is normally secured within 12 in. of every box, cabinet, or fitting and at intervals not exceeding 4.5 ft under 334.30. Flat cable is not stapled on edge, and supports cannot crush the jacket. Type AC uses the 12-in. and 4.5-ft rule in 320.30, subject to its stated exceptions. When Type SE is used as feeder or branch-circuit wiring under 338.10(B), apply the referenced Article 334 installation rules rather than assuming that service-entrance routing rules govern. Under 330.30, Type MC is generally supported at intervals not exceeding 6 ft; cable with four or fewer conductors no larger than 10 AWG is also secured within 12 in. of terminations. Fished and short flexible connection exceptions are specific—do not turn them into a general permission to leave accessible cable unsupported.
Bends cannot damage the armor, jacket, or conductor insulation. NM, UF, AC, and SE generally use a minimum radius of five times the cable diameter. MC depends on sheath construction: interlocked and corrugated sheaths generally use seven times the external diameter, while smooth-sheath MC uses the larger 10- or 12-times rules in 330.24.
Protect cable passing through framing under 300.4. Where the edge of a bored hole is less than 1.25 in. from the nearest wood surface, install a listed steel plate at least 1/16 in. thick or use another permitted protection method. Fittings must secure the cable without damaging it, and the sheath or jacket must extend into the enclosure as required.
Use flexible cord only for flexible work
Article 400 permits flexible cord for pendants, portable luminaires and appliances, stationary equipment connections that facilitate interchange, prevention of vibration or noise transmission, equipment requiring movement, and other listed uses in 400.7. Select a cord type marked for the voltage, temperature, oil, water, hard-service, or outdoor exposure involved.
Section 400.8 generally prohibits flexible cord as a substitute for fixed wiring; running it through holes in walls, ceilings, or floors; routing it through doorways or windows; attaching it to building surfaces except as specifically permitted; concealing it behind building surfaces or above suspended ceilings; or placing it where subject to physical damage. Use strain relief so pull is not transmitted to terminals. Cords are generally installed in continuous lengths without splices, with only the limited repair allowance for specified hard-service cords. A cord cap and receptacle do not legalize an extension cord used as permanent premises wiring.
Which cable is generally suitable for a wet-location underground branch circuit when identified for direct burial?
Which statement correctly distinguishes Type AC from ordinary Type MC cable?
A cable is marked only Type USE. Which conclusion is correct?
Which use of flexible cord is generally prohibited by 2017 NEC 400.8?