by Randy Hunter
I
n the last article, we discussed cable wiring methods. Continuing in Chapter 3, we find ourselves
considering the various raceway systems used in
electrical installations. We will be covering the various raceway Articles from 342 to 362, and we are still
using the 2011 National Electrical Code. Again, we
will be discussing just those articles that are commonly used in combination electrical inspections.
First, let’s review the layout of these articles. Gener-
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ally speaking, they have similar formats: 3xx.10 deals
with “uses permitted” and 3xx.12 contains “uses
not permitted”. At times, there will be no “uses not
permitted” section if there are no specific issues, such
as in Article 342 and 344. In some of these articles,
there will be a 3xx.14 that addresses dissimilar metals.
This topic needs to be addressed with some of the
materials used in order to prevent galvanic corrosion,
which can result in a failure to the raceway system.
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Photo1. In these photos, we have EMT and RMC installed in a
facility; both of these installations show good workmanship.
Where the raceway is acting as the grounding path,
corrosion could have a really drastic result.
Next, you will find 3xx.20 Size, which will describe any size limitations, including the minimum
and maximum sizes permitted for each type of
raceway. The number of conductors allowed in the
systems can be found in 3xx.22, which will refer you
to the appropriate location elsewhere in the code
and to the tables you need to use. Also in this section,
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mention may be made regarding cables and when
and how they may be installed in the raceway. Sections 3xx.24 and 3xx.26 contain information regarding Bends, including how to properly make them and
the limits on how many are allowed.
Note that bending of non-flexible conduit requires
specific tools, so make sure the proper tools are being
used. The use of the correct tools insures the system
is not damaged and maintains the proper dimensions
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Photo 2. In the upper photo, it appears to be EMT installed as artwork; however, it still contains conductors and therefore is still subject to the code. If my math skills haven’t failed me, it appears that each run is well over 360 degrees
of bends. In the lower photo, my first question was “Did the contractor own a bender?” The occupants of the facility
confirmed my thoughts and informed me that the installers weren’t electricians.
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Photo 3. As an inspector, you have to keep your eyes peeled; here we have PVC on the left that was bent using a torch,
which has resulted in damage to the conduit. On the right, I’m not even sure it is an approved conduit, it might just be
automotive muffler piping which is welded to create a raceway.
and integrity of the material. Driving a truck over a
conduit that has been placed on a raised curb in order
to bend it is not an approved method; yes, I’ve seen
this attempted! Similarly, a torch is not the approved
method for heating and bending PVC, as we have
specific equipment to heat PVC without damaging it
in order to create bends.
The number of bends is consistent in the code,
which states that the maximum will be the equivalent
of four quarter bends (360 degrees total) between
pull points. The code does not address whether the
bends have a small or large radius; a bend is a bend.
Often I have had contractors say that they made a
long radius bend, so I should allow a little code relief.
While large radius bends may make pulling easier,
the code doesn’t offer relief for the number of bends
based on the radius. The other issue is that short
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radius bends make it harder to pull stiffer conductors
through. There are good reasons for the limits on the
number of bends; if there are too many bends, the
pulling friction on the conductors is likely to cause
damage to the conductor insulation. Remember, the
360-degree rule is the maximum; when installing
conductors, fewer bends are better for labor and provide insurance against damaged conductors.
The next item in some of the articles is 3xx.28,
which deals with the Reaming and Threading issues
related to the specific type of raceway. All cut edges
shall be reamed or otherwise finished to remove
rough edges. There are several tools available that will
do this in a professional and time efficient manner.
This seems like a very basic requirement, but it is
often overlooked by some of our installers. Failure
to ream the edges can lead to damaged conductors,
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shorts and other related failures. As both a master electrician and inspector, when I would come onto a job to
check it, I would randomly stick my finger down inside
the connectors to verify that the raceways had been
properly reamed. This is a very basic code requirement,
but don’t get complacent about it.
Field cut threads on raceways that are threaded also
have a couple of items to verify. First, they are to be
cut with a taper thread, which is a standard cutting die
with a taper of 1 in 16 (3/4 inch taper per foot), this
is an essential requirement. Also, look for threading
which may be done for an extended length, as this will
cause an issue with the mating female threaded devices
bottoming out and not creating a good tight threaded
joint. There is a short raceway, or nipple, which is
called running thread. It is cut on a straight thread
die and has a special use. This cannot be duplicated
on normal raceways using the tapered die, so just be
aware. Also, field-cut threads on raceways which have
a specific coating to resist corrosion must have a fieldapplied protectant applied to the fresh cut threads to
prevent these from damage over time and environmental exposure. Commit the taper to memory if you are
going to take a test for either inspector certification
or electrical trade certification, as this is one of the
standard test questions.
Continuing with the article layout, 3xx.30 deals
with Securing and Supporting. One thing to keep in
mind here is the difference between securing and supporting. The code language states that you will securely
fasten the raceway within a certain distance of any
box, cabinet or other termination. This is pretty easy
to picture, as it will require some type of device that is
designed and properly installed to make the raceway
secure. Securing prevents motion between the connection point and the raceway, which might lead to a loss
of solid contact. If we have a loosening of this type, it
could create a faulty ground path for the system, which
could then lead to overcurrent devices not operating
or a fire hazard. Let’s consider the difference between
support and securement. Picture this: if you hold your
hand up in the air and simply create a saddle with your
hand to hold something without grasping it tightly in
your hand, you are supporting it. However, you are
not securing it, only offering support. When you are
running a conduit on a vertical wall, the supports and
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securement methods may be one and the same; however, when running through framing members that
have openings provided or drilled, then support will
be provided by these openings, but not securement.
Continuing in the articles, we come to the 3xx.42,
46 and 56, which give you the information needed to
enforce Couplings and Connectors, Bushings, and
Splices and Taps. These will vary according to each
raceway system, so review these and become familiar with the requirements for the systems you most
commonly see. This is a good opportunity to review
all of the systems at least once, and then you can
always check the code book when you come across a
new method in the field. Don’t feel like you need to
memorize each part of every raceway system. If you
are not sure of the requirements while you are on
site, just excuse yourself for a moment, go out to your
vehicle, get your code book out and double check.
Once you know the layout of these articles, it makes
it very easy to find your information quickly. If you
really want to have some fun, ask your contractor if
they have a code book so you can check something.
You might be surprised at the answers you get. I’ve
had contractors offer me code books that are over a
decade old and others that just don’t have one close
by. I wonder what they do if they have a question on
an installation or code application issue?
If any of the raceways have an added requirement
for grounding, it should be mentioned in 3xx.60 of
the respective article. This section will also tell you if
the raceway itself is suitable for grounding.
The last general article layout item I want to
mention is Part III of each article, which deals with
Construction Specifications. Marking requirements
will be covered here, and this may be a lot of help if
you have a question when you see something that
just doesn’t look right or is a method you haven’t
seen before. Also, Part III may give you additional information related to such things as standard lengths
of the respective conduit system.
Now we’ll look at a few specific raceway types.
We will start with Articles 342 and 344, Intermediate Metal Conduit (IMC) and Rigid Metal Conduit
(RMC). While very similar as far as applications, I
will point out the differences between the two and
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Photo 4. Here is a photo of both sides of a PV system
showing the inverters and the panel they feed; notice
here that the raceways used to transition from the underground raceway system to the various pieces of equipment are all Liquidtight Flexible Metal Conduit.
then go into the code applications. Intermediate
Metal Conduit was developed in the 1970s. It is a
less expensive alternative to RMC due to its reduced
wall thickness. It has an external galvanized coating
for protection, and the interior has an organic coating
for corrosion protection. Both IMC and RMC have
a 3/4 inch per foot tapered thread, which makes the
fittings interchangeable.
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Rigid Metal Conduit may be made of steel, stainless steel, aluminum or red brass. Several acronyms
are used, some of them are RSC (Rigid Steel Conduit), ERSC (Electrical Rigid Steel Conduit), GRC
(Galvanized Rigid Conduit), and of course RMC
(Rigid Metal Conduit). Rigid Steel Conduit is the
heaviest-weight and thickest wall conduit. It is generally protected by a zinc-based coating. For more
details on these conduit systems, you may visit the
Steel Tube Institute website.
The next raceways we’ll cover are found in
Articles 348 Flexible Metal Conduit (FMC), 350
Liquidtight Flexible Metal Conduit (LFMC), 356
Liquidtight Flexible Nonmetallic Conduit (LFNC),
360 Flexible Metallic Tubing (FMT), and finally
362 Electrical Nonmetallic Tubing. The one thing
all of these methods have in common is that they
are a flexible raceway system. Early on in the
electrical business, they recognized that there was
a need for a flexible conduit system, so along with
this recognition came the need for standardization
of products for use in the electrical industry. As a
result, Underwriters Laboratory established the first
UL Standard (UL 1) for Flexible Metal Conduit in
February of 1924.
Each of these flexible raceway systems will have
a few unique requirements and applications. One
of the major uses for these systems is providing
the needed flexibility for connection to equipment
that needs isolation from vibration or equipment
that requires movement as a function of its design.
However, each of these methods may have requirements you need to be aware of, especially related
to such things as grounding and bonding. Some of
them may be acceptable for grounding up to certain
lengths and others not at all; some may absolutely
require an additional grounding conductor, depending on the application. Again, you will need to
review the exact article related to the system used.
Sometimes, you may have a local code requirement which requires a separate wire-type equipment grounding conductor in certain wiring
methods, usually for wiring methods that are flexible metallic type or have non-threaded couplings.
If so, this is done to provide an even more reliable
ground-fault current path.
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Photo 5. Here is a good example of EMT installed in a headwall of a hospital emergency room. Notice the use of colored
EMT to identify the different systems within the facility.
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Next we’ll review the nonmetallic raceway systems, including: 352 Rigid Polyvinyl Chloride Conduit (PVC), 353 High Density Polyethylene Conduit
(HDPE), 354 Nonmetallic Underground Conduit
with Conductors, 355 Reinforced Thermosetting
Resin Conduit (RTRC), and a repeat from the flexible list would also include 362 Electrical Nonmetallic Tubing (ENT).
First of all, these conduit systems require a grounding conductor when used in applications where
grounding is required, as they are made of nonmetallic
materials. Therefore, there is no way the raceway itself
will provide a grounding path back to the origin of the
circuit. Another item to be concerned with is the support of these wiring methods. When run above ground,
you will have to check the requirements for each
method. For instance, PVC requires support according
to the diameter being installed.
One of the issues you need to address with
nonmetallic raceways is thermal expansion, which
can be exacerbated when installed in areas subject to
large temperature changes. If installing PVC, refer to
352.44 for the code requirements and Table 352.44
for the data, which will give you the expansion coefficient per 100 feet of raceway based on your temperature swing.
Article 354 Nonmetallic Underground Conduit
with Conductors is a system you may not have seen.
I haven’t seen it installed within the portion of the
systems we are required to inspect, in others words
downstream of the point of service. However, I have
seen thousands of feet of this used by the utility on the
service side of the meters. The utility commonly calls
it CIC, or conductors in conduit, and it will come in
large reels and be installed per the utility regulations.
Another issue related to nonmetallic raceways is
that you have to be aware of the temperature limitation of the raceway itself; this will be part of the
labeling or listing requirement. The point of concern
here is that we shall not install a conductor with a
load that would result in it operating at a temperature
that will exceed the rating of the raceway. A good
example of the code language addressing this is
found in the PVC article 352.10(I), Uses Permitted,
Insulation Temperature Limitations. If we were to
have an installation where the conductor operates at
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a temperature higher than the raceway, it would overheat the raceway. This could lead to off gassing from
the conduit, embrittlement of the conduit, or further
overheating issues if the conductor becomes encased
in additional melted PVC.
The last article we will address is probably the
most common raceway system we see used,
Electric Metallic Tubing (EMT), which is covered
in Article 358. One notable fact is that EMT is not
a conduit, it is a tubing. Therefore, elsewhere in the
code if there is a requirement related to conduit, it may
not apply to EMT. It is unique in the fact that it cannot
be threaded, which results in special fittings just for
EMT. It has several advantages, some of which include
price compared to RMC or IMC, weight (it is much
lighter), and it is very easy to do field bends. It meets
the requirements for an equipment grounding path
when properly installed. EMT has fittings which allow
it to be used in both dry and wet locations, depending on the listing of the fittings. One area of concern
with EMT is that where run outside and exposed to
temperature variations, make sure the connectors and
couplers are tight. The last thing we want is to have this
raceway system loosen up and come apart when used
as our equipment grounding conductor.
I’ve taken a different approach to discuss raceways
in the code, describing the arrangement of the Articles,
pointing out a few items of concern, some of the issues
regarding different materials, and some of the inspection items to watch for. Again, I have not gone item by
item within each article, as I expect you to have and
use your code book when reading these article. The
only way to learn the code is to use it and apply it.
Randy Hunter works for Eaton’s Bussmann.
He holds twelve inspections certifications from
IAEI, ICC and IAPMO. Randy is IAEI Southwestern Section secretary, Southern Nevada IAEI
Chapter president, IAEI International Board
member, a former principal member of CMP-6,
current principle member of CMP-17, voting member of UL 1563,
Electric Spas, Equipment Assemblies, and Associated Equipment,
is a member of IAPMO Product Certification Committee and
Standards Review Committee. He has served on several Southern
Nevada local code committees and electrical licensing committees.
He has been a master electrician since 1988, and prior to that he
designed and built computerized numerically controlled (CNC)
machine tools.
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