Wiring for Non Metallic Sheath Cable (NMSC) Flashcards
Bundling of NMSC
Bundling non-metallic sheathed cable together (increases the temperature of the cables - due to mutual heating - decreases efficiency of heat dissipation.
600 mm?
Protection of NMSC in concealed locations
Rule 12-516 requires NMSC installed in concealed locations (protect from mechanical damage) - during and after installation
Rule 12-516 1) permits protection plates or cylindrical bushings (approved of course) for installing NMSC through studs, joists or similar members within 32 mm of the edge
Using sectional box sides is not acceptable (for cables within 32 mm of the stud face) (not approved)
Question 1
Where cables are fanned out along the surface of a structural member are are within 32 mm of the edge, does OESC require mechanical protection?
Answer 1
Yes, Rule 12-516 states requirement for NMSC running along the surface of studs, joists or similar members to keep a minimum distance of 32 mm from the edge (that can be covered in drywall or similar materials) - protect cable from a screw missing the stud or joist
if distance can’t be achieved (32 mm) then approved corrosion resistant ferrous metal not less than 1.3 mm thick will be be required to cover width of the cable or group of cables
Rule 12-516 3) - permits use of NMSC with metal stud construction
-requires approved inserts (grommets) secured in place (to protect cables) where it passes through the metal stud in accordance with Rule 12-516 3)
Round inserts are approved for a given size opening in a steel stud. If loose fitting or easily removed then not adequate and should be replaced or installed in properly sized holes
-lead to cable failure
Question 2:
is it acceptable to fish NMSC into a metal stud wall?
Answer
No, Rule 12-520 does not permit cables to fished where metal joists, metal top or bottom plates, or metals studs are used
Wiring method for NMSC in wall construction with rigid foam insulation
(ICF) Insulated concrete form - the drywall (wall finish) can be fastened to supports embedded in the rigid insulation
questions:
depth of cable channels into the insulation behind the interior wall finish
acceptable outlet box installation methods
NMSC is acceptable for this kind of insulation
- no need to space NMSC away from the finish wall surface - other than drywall attachment supports - must comply with Rule 12-516 (conductors spaced 32 mm back from edges of the supports or mechanical protection must be provided)
if the cables installed in the channels cut into the foam - the bundling requirement in any channel are outlined in Topic 1) in this Bulletin
Usage of spray foam polyurethane insulation in walls that already have NMSC installed in compliance with OESC is also acceptable
If ICF is used as a permanent form for poured concrete, boxes should be fastened to the structural member that is integral to the form
or through the back of the box to the concrete behind the rigid insulation using two fasteners - required by Rule 12-310 1)
Boxes with a flat rear surface (masonry type boxes or one piece utility boxes - are suitably spaced to ensure the front edge structural members is used (attach concrete behind box with two fasteners)
Where ganged sectional boxes are used - additional support is required Rule 12-3010 (additional concrete support)
NMSC in buildings of non combustible construction
The jacket on NMSC is typically rated FT1 - which is not ineligible for use in buildings required to be of non combustible construction in accordance with the Ontario Building Code (OBC) - referenced by Rule 2-130 and Bulletin 2-8)
But OBC does permit cables with combustible jackets - where installed in a totally enclosed metallic raceway or a totally enclosed non-metallic raceway
-Extension of the cable into bulkheads or concealed ceiling spaces is in violation of the OBC
Number of NMSCs per outlet box knockout
The OESC does not permit more than one NMSC per pry out using internal clamp.
CSA Standard C22.2 No. 18 (Outlet Boxes, conduit boxes, and fittings) tests pullout and voltage withstand after exposure to an elevated temperature are done with one cable per clamp
Use more than one cable per clamp is a misapplication
The standard does recognize box connectors that are approved to accommodate more than one cable and such connectors can be used with more than one cable, up to limit stated by the manufacturer
Mechanical protection and support for NMSC
In attic or roof spaces
Rule 12-514 1) a) requires exposed NMSC to be protected from mechanical damage on the upper face of a ceiling joist or lower face of a rafters in attic or roof spaces with the use of a guard strip when the distance between the joists and rafters exceeds 1 m.
Size if guard strip dependent in location
upper face of a ceiling joist - Rule 12-514 4) - requires the board to be at least 38 mm x 38 mm in size
Rule 12-514 2) requires the board to be sized at least 19 mm x 38 mm on the lower face of a roof rafter
What is the maximum distance a NMSC can be installed from the edge of a guard strip when installed on the upper face of a ceiling joist or on the lower face of rafters in an attic or roof space?
Answer 3
100 mm.
Additionally guard strip will be required on opposite side of the NMSC if distance cannot be achieved
Rationale 3
intention to prevent damage to the conductors while walking in attics during and after construction, as well as storage of material in non- insulate areas
Diagram B1 – Mechanical protection of NMSC installed in the attic and roof space
b) On the lower face of exposed ceiling joists
Rule 12-514 1) b) requires exposed NMSC to be protected from mechanical damage on the lower face of exposed ceilings. Questions have arisen concerning acceptable mechanical protection, where NMSC is installed on the lower faces of ceiling joists. Cables installed adjacent to ducting with an air space no closer than 25 mm as required in accordance with Rule 12-506 4), beams or by location are considered as being suitably protected. Where cables are not in close proximity to ducts or beams, mechanical protection is required. This may be achieved by the use of guard strips sized at least 19 mm x 38 mm in accordance with Rule 12-514 2). Some representative situations are shown in the Diagram B2.
Question 4
What is the maximum distance a NMSC can be installed from the edge of a guard strip when installed on the lower face of a ceiling joist?
Answer 4
100 mm. An additional guard strip will be required on opposite side of the NMSC if distance cannot be achieved. Note: Objective is to not exceed the 100 mm distance from a guard strip. See Diagram B2.
Diagram B2 – Mechanical protection of non-metallic-sheathed cable installed on the lower faces of ceiling joists
c) Within the island/peninsular cabinet
Question 5
What are the OESC requirements for mechanical protection of NMSC installed within the island/peninsular cabinet?
Answer 5
Rule 12-518 requires NMSCs to be protected from mechanical damage where they pass through floors, are located less than 1.5 m above a floor or where they are exposed to potential damage. Therefore, where NMSC passes through a floor within the island/peninsular cabinet; or where NMSCs are installed within the cabinets, they require mechanical protection, unless protected by location.
Rationale 5
If NMSC is installed within the island/peninsular cabinet so that opening or closing the drawers can damage the cable; or if a cable is exposed to damage when people are storing items in the cabinet, mechanical protection is required by Rule 12-518 to protect the cable.
Means of mechanical protection may consist of flexible conduit, wood channel or other means which will provide adequate protection.
If a cable is protected by a built-in appliance, such as dishwasher , behind the plumbing pipes or below the countertop, not accessible to people storing items in the cabinet below, NMSC is considered to be protected by location.
Question 7
Is it acceptable to pass NMSC through the sides of a return air plenum, boxed with sheet metal?
Answer 7
Yes, Rule 12-516 3) permits the passing of a cable through the return air plenum if it is protected where it passes through a member by an insert approved for the purpose and adequately secured in place.
e) Where NMSC is dropped from a ceiling or wall to appliances
NMSC that is used in exposed wiring shall be adequately protected against mechanical damage, as required by Rule 12-518, where it is installed at a height of less than 1.5 m above the floor or anywhere else it is exposed to mechanical damage. Examples of this include a cable drop from a ceiling or a wall to appliance such as furnaces, water heaters, etc.
d) NMSC in a residential return air plenum
Question 6
Is it permitted to fish NMSC lengthwise in a residential return air plenum, boxed with sheet metal?
Answer 6
No, Rule 12-520 does not permit cables to fished where metal sheeting or cladding, metal joists, metal top or bottom plates, or metal studs are used.
Photo B4 shows an example of the mechanical hazards that may be encountered f a cable is fished through the cold air return in a dwelling unit.
Photo B4 – An example of the mechanical hazards that may be encountered if a cable is fished through the cold air return in a dwelling unit
