Codes & Standards
Slabs, EMT and vapour barriers: Rule 12-1414 • David Pilon
By David Pilon
August 10, 2016 – The building code defines a vapour barrier as “the elements installed to control the diffusion of water vapour”. Did you notice it says “control” not “eliminate”?
C22.1-15 Rule 12-1414 now requires a bond wire in EMT when installed in concrete or masonry slabs that are in direct contact with the earth, or wet or outdoor locations.
When a vapour barrier is installed on a wall, it allows the diffusion of water vapour through the interior finish. So when a vapour barrier is installed below a concrete slab, does it mean the concrete is no longer interpreted as “in direct contact with moist earth”? Well, the vapour barrier is diffusing water vapour into or through the concrete; I interpret this as concrete being in direct contact with the earth.
Vapour barrier installation changes over the years, addressing questions around sealing, cutting and bleeding, and whether the aggregate will remain wet, therefore keeping the location wet. (With regard to the latter, an advantage with a completely sealed vapour barrier is a slower curing time.)
Current thinking holds that concrete should be placed directly on a sealed vapour barrier. Now, we need to remember what we read earlier: the barrier controls the diffusion of moisture, but does not eliminate it. Therefore, a concrete slab should be considered in direct contact with the earth, regardless of a vapour barrier. This location requires a bond conductor, as this is a damp location and may be somewhat corrosive.
With this information, we can determine the type of conductor required when pulled into a conduit, installed in a concrete slab (with vapour barrier) in direct contact with the earth. Rule 4-008 tells us conductors shall be of a type (as per Table 19) for the specific condition of use, such as moisture, corrosion, temperature, type of raceway, exposure to mechanical damage, and harmful vapours or organic solvents that may contact the conductors.
Rule 12-1404 was added to define the restrictions on EMT, clarifying its use in a corrosive location. When using one of the exempted methods, a bonding conductor should also be installed to conform to Rule 10-602 to ensure continuity of the fault return path.
Lastly is the new Rule 12-1410, which refers to the maximum number of conductors in a conduit. Note, Table 8 still specifies the maximum fill percentage for each raceway, and Rule 12-910 clearly explains the methods for calculating the conduit fill. Rule 12-910 directs us to Tables 9A-9J for each raceway type, and to Tables 10A-10D for single conductor dimensions. Other than the extra tables for each varying type of raceway (and the addition of a table for solid conductors and DLO cables), the math is the same.
David Pilon has been an electrical inspector with SaskPower since 2000, and is currently the vice-chair of the Canadian Certified Electrical Inspector (CCEI) committee of the International Association of Electrical Inspectors (IAEI), Canadian Section. David can be reached at email@example.com.
N.B. Always consult your AHJ for more specific interpretations.
* This article also appears in the August 2016 edition of Electrical Business Magazine. Check out our ARCHIVE page for back issues.