Both the Canadian Electrical Code and its
American counterpart, the National Electrical Code provide similar definitions for the metallic means of bonding
electrical equipment and raceways. In this article, I’d like
to review some of the similarities and differences in the
acceptable bonding methods in Canada versus the United States.
Let’s begin with the definition of bonding as
expressed in our separate electrical codes.
According to the CE Code, bonding is
"a low impedance path obtained by permanently joining all
non-current-carrying metal parts to assure electrical
continuity and having the capacity to conduct safely any
current likely to be imposed on it."
According to the NEC, bonding is
"the permanent joining of metallic parts to form an
electrically conductive path that ensures electrical
continuity and the capacity to conduct safely any current
likely to be imposed."
As you can see, although some of our words
are different and re-arranged in a different format, both
definitions provide the same, understandable overall
objectives. There is a greater difference in the words used in
our separate electrical codes to describe bonding methods.
Canada’s CE Code uses the term bonding conductor to
define the methods we use for equipment bonding. The NEC term uses equipment grounding conductor. (This is
sometimes a source of confusion when we use American
literature. We really should get together on a common
definition.)
But here is where our similarities come to
an abrupt end. Both electrical codes have a common list of
bonding methods recognized in both countries. But the NEC goes much further, offering a wider range of permissible
options than our CE Code. I have italicized the bonding
methods permitted by the NEC that are not used in
Canada in the following bullets.
The Canadian Electrical Code permits the
following materials to be used as bonding conductors:
· Copper conductors
or other corrosion-resistant material (usually aluminum)
· Metal busbar or
pipe
· Rigid metal
conduit (except stainless steel, directly buried, in concrete
or masonry that is in contact with the earth or where
corrosion or damage is probable)
· Electrical
metallic tubing (except in concrete or masonry in contact with
the earth or where corrosion or damage is probable)
· Copper or aluminum
sheaths or the marked conductors of mineral-insulated cable
(except that cables with aluminum sheaths require corrosion
protection as necessary)
· Sheaths of
aluminum-sheathed cables (with corrosion protection as
necessary)
The National Electrical Code permits
a far broader range of materials that may be used as equipment
grounding conductors, some with numerous conditions and
therefore some of the methods of use appear to be fairly
complex:
· Copper, aluminum
or copper-clad aluminum conductors
· Rigid metal
conduit
· Intermediate
metal conduit (a type of conduit not
recognized by the CE Code)
· Electrical
metallic tubing
· Flexible metal
conduit when both conduit and fittings are listed for
grounding ("listing" is
the American equivalent of the CE Code term
"approval")
· Flexible metal
conduit unlisted for grounding (when
used with listed fittings, maximum 20-amperes circuit
overcurrent protection, up to 1.8 m in length and installed
for purposes other than to provide flexibility)
· Flexible metal
tubing with fittings listed for
grounding (circuit protection up to 20 amperes and up to
1.8 m in length)
· Armour of
armoured cables (when it is
installed using methods so that it provides an effective fault
path)
· Copper sheaths of
mineral-insulated cables
· Type MC
metal-clad cables where listed for grounding (using
a combination of either bonding conductors and interlocked
metal tape or bonding conductors and metallic sheaths)
· Cable trays (when
identified for grounding purposes, of suitable cross-sectional
area and so marked, with properly selected connections or
bonding jumpers and maintained by qualified personnel)
· Cablebus
framework (for branch circuits and
feeders only)
· Electrically-continuous
metal raceways and auxiliary gutters listed for grounding
As you will notice, our Canadian Electrical
Code is more prescriptive and permits only a narrower range of
methods for bonding electrical equipment and raceways. The NEC is more objective based — it offers further ways of
achieving the same result, but with lots of conditions. It
also appears that the NEC provides more flexibility,
but demands a more advanced level of knowledge when selecting
and applying some of the available bonding options. Being more
prescriptive, the CE Code is more rigid, offers fewer options,
but more simple to interpret and apply. Which do you think is
more practicable?
As with past articles, you should always
consult with the local electrical inspection authority in each
province or territory for a more authoritative interpretation
of any of the above.
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. |
