Canadian Electrical Code users have no
doubt noticed the reminder (see Appendix B) next to the
headings of many code rules. Appendix B is there to help us
understand and correctly interpret the requirements of the
code. It provides supplementary information including
explanations, interpretations, other standards and sources of
information to assist users in applying the rules so
identified. It also gives us a better idea of what an
inspector will expect. It’s a very good idea, in particular
when applying a rule for the first time, to take a look at
what Appendix B has to say.
In order to expand on the above, this
article will identify a few of the rules that include this
notation, with some examples of the types of important
information provided, that can help us meet the requirements
of these rules.
Rule 2-126 simply specifies that the
minimum flame spread requirements for wire and cable must meet
the specifications of the building code. But if you go to
Appendix B, you will find a great deal more useful information
including:
• The relevant building code paragraph
numbers that provide minimum flame spread ratings for
different types of construction
• The required wire and cable
identification markings
• Acceptable installation methods for
wire and cable that are unmarked and may not have the
necessary flame spread ratings
Rule 2-128 requires that nonmetallic
conduit run exposed in buildings of noncombustible
construction must meet the requirements of the building code.
Appendix B provides added information on the maximum trade
size and required marking for conduit so installed.
Rule 4-004(1) and (2) permit wiring
ampacities other than provided in Tables 1 to 4 of the
electrical code through the use of IEEE Standard 835. To the
chagrin of anyone who has contemplated using this method of
calculation, Appendix B provides almost two pages of direction
on minimum data that must be submitted to electrical
inspection to justify using the IEEE Standard 835 as an
alternative to the electrical code tables.
Rule 10-500 requires that the ground faults
must have a low impedance return path so that they may be
safely interrupted. Appendix B provides further essential
information, requiring that the impedance be sufficiently low
so as to permit 5 times rated current to flow during a ground
fault, so that fuses or circuit-breakers can do their jobs
effectively, without harm to persons or damage to property.
Rule 10-814(1) requires that the data
specified in Table 16 be used to select minimum bonding
conductor sizes. However, the rule is silent on minimum
requirements when metallic cable sheaths or metallic conduit
are used for bonding electrical equipment. Appendix B takes on
this task, spelling out that when cables or conduits are
correctly sized for other purposes, the metallic sheaths or
conduit will automatically be correctly sized for the
intention of bonding.
Rule 12-1104(1) tells us that rigid PVC
conduit must not be exposed to temperatures in excess of
75°C. But Appendix B clarifies this requirement by advising
that wiring having 90°C temperature ratings, when
continuously loaded under conditions of 50 percent conduit
fill, in a 30°C ambient will not result in temperatures above
75°C. Therefore, 90°C rated conductors in PVC conduit may be
loaded up to their 90°C ratings and conductors having
insulation temperature ratings above 90°C may also be
installed in PVC conduit when their allowable ampacities are
derated to 90°C.
Rule 12-2200 requires that cable trays be
supported in accordance with support spacings provided by the
cable tray manufacturer. But Appendix B adds some further
conditions:
• The best support points are at the one
quarter span points
• There must not be more that one joint
between cable tray supports
• Some fittings (especially horizontal
fittings) may need additional supports
Rule 26-256 stipulates that the primary
overcurrent protection for dry type transformers must not
exceed 125 percent of the rated primary current of the
transformer. Appendix B offers additional valuable information
— that fuses or circuit-breakers should be able to carry 12
times the primary load current for .1 second and 25 times the
primary load current for .01 seconds so as to avoid unintended
power outages due to inrush currents.
Rule 26-354 requires that transformer
vaults meet the special construction, drainage, ventilation
and lighting requirements of the building code for such
facilities. Appendix B identifies the relevant building code
paragraphs that provide this information.
Rule 30-322 specifies that a switch
controlling bathroom lighting must be out of reach of a person
in a tub or shower. Appendix B interprets "out of
reach" as one metre.
As mentioned above, Appendix B contains an
abundance of valuable and often critical information and it’s
there for our use and convenience.
As with other articles, you should consult
your local electrical inspection authority for a more precise
interpretation of any of the above information.
Leslie Stoch, P.E. is principal of L.
Stoch & Associates, providing electrical engineering
and ISO 9000 quality systems consulting. Prior to that,
he spent over 20 years with Ontario Hydro as an
electrical inspection manager and engineer. Les holds a
B.S. in electrical engineering from Concordia University
in Montreal. |
