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Ref. NEC Article 348
Electrical Metallic Tubing (EMT) is simi-
lar to rigid steel conduit but is much
lighter, weighing approximately 40 per-
cent as much as rigid steel conduit of
the same nominal size. EMT can be
used for both exposed or concealed
work provided, where during installa-
tion or afterwards, it is not subjected to
severe physical damage. Use of EMT
is restricted to systems not exceeding
600 volts and to non-hazardous loca-
tions except (Class II Division 2 NEC
Section 502-4 (b).
Galvanized Steel EMT installed in
concrete on grade or above generally
requires no supplementary corrosion
protection. However, when installed in
concrete below grade level and in con-
tact with soil or cinders supplementary
corrosion protection consisting of a
protective coating of bitumastic or
asphalt base paint or plastic is gener-
ally applied. According to NEC Section
348-1, EMT run in or under permanent-
ly moist cinder fill must be encased in
at least two inches of cinder free con-
crete unless the conduit is at least 18
inches below the fill.
Aluminum EMT cannot be directly
embedded in concrete containing sol-
uble chlorides such as calcium chlo-
ride, unwashed beach sand, sea water
or coral bearing aggregates. When
adequately treated with a protective
coating of bitumastic or asphalt base
paint or plastic coating the raceway
can be installed in concrete containing
chlorides.
NEC Sections 384-4 and 300-6
require that in wet locations where
walls are frequently washed or where
there are surfaces of absorbent materi-
al the entire wiring system including
boxes, fittings, conduits and cables
must be supported such that there is at
least 1⁄4inch air space between it and
the supporting surface.
Connectors and couplings are
required to be of concrete tight type
when embedded in masonry or con-
crete or in dry locations and of the rain
tight type when installed in wet loca-
tions (NEC Section 348-8).
According to NEC Section 373-6,
where No. 4 or larger underground
conductors enter or leave a conduit, an
insulating bushing with a smooth well
rounded insulating surface must be
provided to protect conductors, unless
the terminating fitting is equipped with
an insulated throat, firmly secured in
place providing equivalent protection.
The insulating bushing or insulating
material must have a temperature rat-
ing of not less than the insulation tem-
perature rating of installed conductors.
NEC Section 300-10 requires that
the raceways be metallically joined
together into a continuous electric con-
ductor and must be mechanically con-
nected to all boxes, fittings and cabi-
nets as to provide effective electrical
continuity.
EMT is not permitted to be thread-
ed. Cut ends of tubing are required to
be reamed. Code requires that EMT be
adequately supported and restricts
bends in one run to the equivalent of
four quarters i.e. 360 degrees total.
Portions of this section reprinted by
permission from NFPA 70-1978,
National Electrical Code®, Copyright©
1977, National Fire Protection
Association, Boston, MA.
For further details and complete infor-
mation please refer to the following:
1. NEC Article 348…Electrical
Metallic Tubing
2. ANSI C80.3…Electrical Metallic
Tubing, Zinc Coated,
Specifications for
3. ANSI C33.98, UL797…Standards
for Safety. Electrical Metallic
Tubing.
4. Fittings for Rigid Metal Conduit
and Electrical Metallic Tubing,
Specifications for
5. U.L. 514B, Standards for Safety,
Outlet Boxes and Fittings
6. WW-C-563…Conduit, Metal, Rigid,
and Bend and Elbow, Electrical
Conduit, Thin-wall Type (EMT)
7. W-F-408…Fittings for Conduit,
Metal, Rigid, (Thickwall & Thinwall
(EMT) Type)
8. NEMA FB-1…Standards
Publication. Fittings and Supports
for Conduit & Cable Assemblies.
9. CEC Section 12-1500…Electrical
Metallic Tubing
10. CSA C22.2 No. 83…Safety
Standards for Electrical Metallic
Tubing
11. CSA C22.2 No. 18…Safety
Standards for Outlet Boxes,
Conduit Boxes and Fittings
Electrical Metallic Tubing (EMT) Fittings
Electrical Metallic Tubing (EMT)
Please Note
The excerpts and other material herein, whether relating to the
National Electrical Code, the Underwriters Laboratories, Inc. list-
ing, to industry practice or otherwise, is not intended to provide all
relevant information required for use and installation. Reference to
original or primary source material and data is mandatory before
any application or use is made of the product.
A
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