electrical wire in cold air return

[ck_chino]

Hey Guys
Whats the deal with electrical wires in cold air return? Specifically in Brampton, Ontario if it matters.  I understand its ok to run through, intersect a cold air return perpendicularly, but what about along within the vent parallel?

[Admin]

See the attached picture from OESC Bulletin 12-19-12.  These days it's common to see a cardboard thermopan used to line the joists and act as a return air plenum.  It's not constructed of metal so I'm not sure if the same rules apply to it.  As far as I know, AC90 wiring has an FT6 fire rating and is permitted to be installed within spaces being used as a return air plenum.  This is armoured wiring that people call BX wiring.  You will still need to secure the wiring and can't just leave it sitting inside the return air.  I would double check with an ESA inspector to be sure though, as I am not an electrician.

From the OESC 26th Edition,

12-010 Wiring in ducts and plenum chambers
(1) No electrical equipment of any type, unless specifically approved for the purpose, shall be installed in ducts used to transport dust, loose stock, or flammable vapours.
(2) No electrical equipment, unless specifically approved for the purpose, shall be installed
(a) in any duct used for vapour removal or for ventilation of commercial-type cooking equipment; or
(b) in any shaft that is required by regulation to contain only such ducts.
(3) Where conductors are installed in ducts, plenums, or hollow spaces that are used to transport or move air as part of an environmental air system or in a duct or plenum chamber to connect to an integral fan system, the conductors shall be in accordance with the requirements of Rules 2-130 and 12-100.
(4) Notwithstanding Subrule (3), where a plenum or hollow space is created by a suspended ceiling having lay-in panels or tiles, flexible cord not exceeding 3 m in length and terminated with an attachment plug shall be permitted to supply pole-type multi-outlet assemblies provided that the flexible cord is listed in Table 11 for hard usage and the supply voltage does not exceed 300 V.
(5) Where a furnace cold-air return duct is formed by boxing in between joists, wiring methods specified in this Section for use in the particular location shall be permitted to be used.

Rule 2-130
The flame spread requirements for wiring and cables in buildings are located in the National Building Code of Canada as follows:
(a) combustible building construction — Article 3.1.4.3;
(b) non-combustible building construction — Article 3.1.5.18; and
(c) plenum spaces in buildings — Article 3.6.4.3. The markings for wires and cables meeting the flame spread requirements of the National Building Code of Canada (without additional fire protection) are
(a) FT1* — wires and cables that are suitable for installation in buildings of combustible construction;
(b) FT4† — wires and cables that are suitable for installation in
(i) buildings of non-combustible and combustible construction;
(ii) spaces between a ceiling and floor, or ceiling and roof, that may be used as a plenum in buildings of combustible construction; and
(c) FT6‡ — wires and cables that are suitable for installation in
(i) buildings of non-combustible and combustible construction; and
(ii) spaces between a ceiling and floor, or ceiling and roof, that may be used as a plenum in buildings of combustible or non-combustible construction.

Wires and cables with combustible insulation, jackets, or sheaths that do not meet the above classifications but are located in
(a) totally enclosed non-combustible raceways;
(b) masonry walls;
(c) concrete slabs;
(d) a service room separated from the remainder of the building by a fire separation having not less than 1 h fire-resistance rating; or
(e) totally enclosed non-metallic raceways conforming to Rule 2-132 may be considered to comply with the National Building Code of Canada requirements relating to flame spread. It is the intent of this Rule to limit flame spread and smoke propagation of cables in plenum spaces to the values specified by Article 3.6.4.3 (1) (a) of the National Building Code of Canada. Authorities enforcing provisions of the National Building Code of Canada and the National Fire Code of Canada in each jurisdiction should be consulted in order to determine the acceptable volume of wires and cables in plenums for the purpose of conformance with the National Building Code of Canada and the National Fire Code of Canada requirements.

Sentence 2.4.1.1 (5) of the National Fire Code of Canada (2010 edition) requires that, when located in plenum chambers, abandoned optical fiber cables and electrical wire and cables with combustible insulation, jackets, or sheaths be removed except when
(a) the cables or raceways are permanently enclosed by the structure or finish, such as inside a wall located in a plenum;
(b) the cables or raceways are not capable of being removed without disturbing the building structure or finish, such as when embedded in plaster, cement, or similar finish; or
(c) there is a risk that the removal of the cables or raceways will affect the performance of cables in use. For example, if abandoned cables are located in a cable tray together with cables in use and their removal could adversely affect the safety or performance of the cables in use, then the abandoned cables can be left in place.

Rule 12-100
Table 19 indicates the maximum allowable conductor temperature for various types of building wires and cables.
Where the surface temperature and/or the temperature on the insulation of conductors, cable assemblies, or raceway systems exceeds 90 °C, such assemblies are a potential fire hazard if installed adjacent to combustible material and, in such cases, the assemblies should be relocated or supported in a manner to remove this potential hazard.

The low temperature marking on conductors indicates compliance with a test at that temperature, as specified in the product Standard, but does not guarantee safe installation at that temperature.

Care should be taken when installing cables at low temperatures. Measures to consider include preconditioning at higher temperatures prior to installation, and avoidance of mechanical shock from dropping the cable, unreeling the cable too quickly, or bending sharply or quickly at bends. Manufacturers should be consulted when further information is desired.