Electrical – Is it safe and legal to tape cable with a damaged sheath

This is what 2008 NEC has to say...

300.22 Wiring in Ducts, Plenums, and Other Air Handling Spaces. The provisions of this section apply to the installation and uses of electrical wiring and equipment in ducts, plenums, and other air-handling spaces

(A) Ducts for Dust, Loose Stock, or Vapor Removal. No wiring systems of any type shall be installed in ducts used to transport dust, loose stock, or flammable vapors. No wiring system of any type shall be installed in any duct, or shaft containing only such ducts, used for vapor removal or for ventilation of commercial-type cooking equipment.

(B) Ducts or Plenums Used for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts or plenums specifically fabricated to transport environmental air. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these ducts and plenum chambers. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted.

(C) Other Space Used for Environmental Air. This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.

FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.

Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces.

(1) Wiring Methods. The wiring methods for such other space shall be limited to totally enclosed, nonventilated, insulated busway having no provisions for plug-in connections, Type MI cable, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory assembled multiconductor control or power cable that is specifically listed for the use, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables, conductors, and raceways shall be permitted to be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers or solid bottom metal cable tray with solid metal covers.

(2) Equipment. Electrical equipment with a metal enclosure, or with a nonmetallic enclosure listed for the use and having adequate fire-resistant and low-smoke-producing characteristics, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere in this Code.

Exception: Integral fan systems shall be permitted where specifically identified for such use.

After reading subsection (C), it looks like nonmetallic cable is not allowed in ducts unless it's in conduit.

Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air.

Which means you can't have equipment in the ducts that is not part of the HVAC system itself. So a junction box for a light, would not be allowed (unless the light is inside the duct for maintenance purposes).

If your local government follows National Electrical Code (NEC), then you should not install a junction box for the light in the duct. If you don't follow NEC, it's still probably a bad idea. The boxes and cable are a good place for dust, dirt, and debris to collect. And the cables and equipment could be damaged during duct cleaning.

Like Shirlock said, this does happen. I have taped a few staple mishaps along the way. Each incident is evaluated differently. If it is a neutral with just the insulation rubbed away (not a compromise to the conductor!). And I was also sure that it was used as a neutral (and not a switched lead). Then I have layed the insulation back and given it a few wraps with the Scotch 33 (600V insulation per wrap!, not the cheap stuff) and felt confident it was safe. Is that code compliant? Will an inspector fail the job if he saw it? Absolutely! The inspector does not know what is behind the tape and is not going to take your word for it. Okay, so obviously you want to sleep at night so here are a few code compliant ideas.

• Add a "deep Handy box" (single outlet box) at outlet height and splice the wire coming from the floor to a new wire going up if you can replace that wire. If the wire is a feed, perhaps include an outlet in the box. If not, just put a blank cover on it. As long as you can get to the box, a proper splice will be code compliant.
• Can't add a box there? How about the other side of the wall? Maybe you will even get lucky and end up in a closet! Only if you're in a closet, you must make it a J-box w/blank cover, outlets, switches are not allowed in closets.

EDIT: I was told by a licensed Electrician awhile ago that it is a code violation to put outlets or switches inside the closet. I never questioned that because all new construction I have seen here in many years has the light switch outside of the door! It made sense, with posible arcing from a switch and clothes and all. I'm thinking it may be a local code requirement. I know he also talked about how you need to do it as the inspector wanted, in addition to NEC code. I did find however that code clearly states that no electrical breaker panels can be in a clothes closet, perhaps its a variation of that?. I have to stand by my friends interpretation, I know he is competent Electrician.