Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02428898 2003-05-14
ELECTRICAL METALLIC TUBE, COUPLING, AND
CONNECTOR APPARATUS AND METHOD
Technical Field of the Invention
This invention relates to the field of tubing. More particularly, the
invention relates to the field of electrical metallic tubing ("EMT") apparatus
including tubing, connectors and couplings, methods of coupling sections of
EMT, and methods of connecting EMT to other apparatus such as junction
boxes or transition fittings.
Background Art
Currently EMT is connected by using one of two methods, either a set
screw coupling or a compression coupling. The connectors are made from either
electroplated steel or from die cast zinc. Set screw EM-f couplings are
sleeves
which slip over the outside diameter of two opposing EMTs. Set screw EMT
couplings typically have an inner ridge to make sure that the two pieces of
EMT
butt up properly to the center of the coupling. The coupling has set screws)
that
penetrate the wall of the coupling and when tightened create both a ground
path
and a tight fit.
Compression couplings are made of three "body parts" plus a split gland
ring. The inner body is threaded on each end and then the split gland ring is
slipped on and then the "outer body" on each end is threaded onto the inner
body. By tightening the outer body ends, the split gland ring is tightened
around
the EMT, providing a tight fit and a good ground path.
In the installation of EMT, provisions have to be made to address the
need for a good ground path. Concerns have frequently been raised by
inspectors and regulators about the integrity of the ground path of steel EMT.
The integrity of the ground path may be degraded if the set screws or
compression sleeves are not tightened fully because electrical continuity
relies
on good, tight connections at each connection or coupling point.
-1-
CA 02428898 2003-05-14
Traditional set screw connectors are basically the same as couplings
except one end is threaded or has some other type of attaching mechanism so
that the EMT can be attached to an enclosure, such as a junction box or some
other piece of equipment that has a knock out hoNe of the correct size for the
connector to fit. Connectors are usually held in pNace with locknuts that lock
the
connector into place and provide a continued ground path.
Existing EMT couplings and connectors require the installer to either turn
a set screw or turn an "outer body." The need to "tighten" a set screw or
"turn"
an outer body not only requires additional work space but is also subject to
human error, such as inadequate tightening. If threaded connections are
subject
to vibration, the screws and/or outer bodies can loosen over time,
compromising
the ground path. Moreover, "twist tightening" increases the time and effort it
takes for mechanics to install EMT. Thus, a need exists for an EMT coupling
and connector system and method that does not require set screw or other
means of twist tightening while still providing a proper ground path.
Currently available snap fit connectors and couplings are expensive to
manufacture and provide a less than optimal ground path.
Disclosure of the Invention
It is an object of the present invention is to provide EMT, connector,
coupling, method for connecting, and method for coupling which are quick and
efficient to install.
It is a further object of the present invention is to provide an EMT, a
connector for an EMT, and a coupling for an EMT that provides a safe and
reliable ground path which does not depend on set screws being tightened and
remaining tightened.
A still further object of the present invention is to provide an EMT, a
connector for an EMT, and a coupling for an EMT that is efficient to
manufacture.
-2-
CA 02428898 2003-05-14
Yet another object is provide an EMT, a connector for an EMT, and a
coupling for an EMT that is easy to use and capable of being used in existing
systems and equipment.
These and other objects are achieved by the present invention which in
one aspect comprises an electrical metallic tube {"EMT") comprising an inner
surface forming an EMT cavity; an EMT outer surface; an EMT first end; and at
least one indentation in the EMT outer surface at or near the EMT first end,
the
indentation adapted to receive a corresponding barb from a sleeve device. The
EMT is preferably manufactured with a number of dimples that are pressed or
punched into the EMT outer surface close to the EMT first end around its
circumference. The number of dimples and the distance from the EMT first end
depend on the size required to meet the necessary pull out tests and other
criteria. The dimples are preferably shaped like a capital D with the flat
side
facing the EMT first end and the rounded side facing the center. The
indentation
can also be a linearly-shaped dimple or roll groove around the entire EMT
outer
surface so there is a continuous area for the barbs of the sleeve device to
snap
into. The indentation is preferably a minimal depth so as to not cause a loss
in
wiring capacity through the EMT cavity..
It is further preferable that the inventive ENIT have an EMT second end
having a mirror image indentation arrangement as the EMT first end,
Preferably,
each length of EMT will have four indentations at or near each of its ends.
Moreover, because the indentation would not be raised above the EMT outside
surface, the inventive EMT can be used with traditional connectors/couplings
available in the market place, which typically slip over the outside diameter
of the
EMT if the inventive couplingslconnectors are not available.
In another aspect, the invention is a sleeve device for connecting EMT
comprising: a sleeve inner surface forming a sleeve cavity adapted to receive
an
end of an EMT; a sleeve outer surtace; a first sleeve end; and at least one
barb
on the sleeve inner surface at or near the first sleeve end. The barb is
adapted
_3_
CA 02428898 2003-05-14
to engage a corresponding indentation on the EMT described above. Depending
on design needs in the field, the sleeve device can be adapted to be either a
coupling or a connector by appropriately designing the opposing end of the
sleeve device.
The sleeve device is preferably designed to have a C-shaped cross
sectional profile and is constructed of spring steel. When the sleeve device
is
used to directly receive an EMT, the sleeve cavity preferably has a diameter
that
is slightly larger than the diameter of the EMT outer surface. When the sleeve
device is used in conjunction with a linking device, as discussed below, the
sleeve cavity will preferably have a diameter that is slightly larger than the
diameter of the outer surface of the linking device. The barbs are designed to
slide over the EMT outer surface and "snap" into the corresponding
indentations
(or the roll groove) on the EMT. Preferably, the barb would point down and
slightly back and will "capture" or "contact" the flat part of the D-shaped
dimple or
linearly-shaped dimple. If the sleeve device needs to be removed from the
inventive EMT, the sleeve device could be spun or twisted and the barbs would
free up as the spinning would result in the barb sliding over the rounded part
of
the (D) or slotted depression. It is preferred that the sleeve device have
four
barbs at or near its first sleeve end for engaging four corresponding
indentations
on the EMT. The barbs help provide a ground path for the EMT by increasing
the area of contact.
It further preferable that the sleeve device further comprise at least one
ground tab formed by a slot in the sleeve device. The ground tab can be bent
downward so that the ground tab would scrape the outer surface of the EMT,
resulting in additional contact area. This helps to enhance the current
carrying
capability and helps to maintain electrical continuity throughout the system.
In order to be able to use the sleeve device on cut EMT or EMT
manufactured without indentations at its ends, the sleeve device preferably
includes a set screw locking mechanism similar to traditional EMT set screw
-4-
CA 02428898 2003-05-14
fittings. This allows maximum flexibility and eliminates the need for the
field
mechanic to carry two types of couplingslconnectors. In this embodiment, the
sleeve device will comprise a set screw hole extending through the sleeve
outer
surface and the sleeve inner surface for threadily engaging a set screw.
When the sleeve device is used to join two lengths of the inventive EMT,
i.e., it is used as a coupling, the sleeve device will comprise a second
sleeve end
having a mirror image barb arrangement as the first sleeve end. Preferably,
there will be four barbs at or near the second sleeve end for engaging
corresponding indentations on the second length of EMT. It is further
preferable
for the connection sleeve to comprise a middle inner ridge on the sleeve inner
surface at or near a center of the sleeve device. Ey sliding the EMT into the
sleeve cavity of the sleeve device and butting it against the inner ridge,
proper
installation is assured.
In yet another aspect, the invention comprises a linking device for EMT
comprising: a first section having a link inner surface forming a link cavity,
a link
outer surface, and at least one barb access hole adapted to allow a
corresponding barb of a sleeve device to extend therethrough when the sleeve
device is fitted around the first section; a second section; and a separator
between the first and second sections.
The linking device is preferably made of die-cast zinc and is designed to
be used in conjunction with the sleeve device. The linking device can be
designed to couple two lengths of EMT together or can be used to connect a
length of EMT to a junction box, splice box, wireway, or other enclosure or
transition fitting.
It is preferable that the first section of the linking device further comprise
a
ground tab hole adapted to allow the ground tab of the sleeve device to extend
therethrough when the sleeve device is fitted around the first section. It is
also
preferable that the first section comprise four barb access holes and a set
screw
hole. The set screw hole should be adapted to be substantially aligned with a
-S-
CA 02428898 2003-05-14
set screw hole on the sleeve device when the sleeve device is fitted around
the
first section. A set screw can be extended through the set screw hole of the
linking device.
The linking device can also comprise an outer ridge around the outside
surface of the first section at a first link end. This helps ensure that the
sleeve
device is properly positioned when fitted around the linking device.
When the linking device is used as a connector, i.e., to connect a length
of EMT to a junction box or other transition fitting, it is preferable that
the second
section be adapted to do so by incorporating a threaded outside surface or a
snap fit assembly on the second section.
When the linking device is used as a coupling, i.e., to connect two lengths
of EMT, the link cavity extends through the second section so that the second
section has a fink inner surface and a link outer surface that mirrors the
first
section. In this embodiment, the second section wilt have at least one barb
access hole, at least one ground tab hole, and at least one set screw hole.
In still another aspect, the invention is a connection assembly for EMT
comprising a combination of the linking device and the sleeve device, wherein
the sleeve device is fitted around the first section of the linking device so
that the
barb on the sleeve device extends through the barb access hole of the linking
device. By varying the design of the second section of the linking device, the
connection assembly can be used to couple two lengths of EMT or connect a
single length of EMT to a junction box or other transition fitting.
In a still further aspect, the invention is an EMT joint assembly comprising:
an EMT having an EMT inner surface forming an EMT cavity, an EMT outer
surface; an EMT first end, and at least one indentation in the EMT outer
surface
at or near the EMT first end, the indentation engaging a corresponding barb
from
a sleeve device; the sleeve device having a sleeve inner surface forming a
sleeve cavity adapted to receive an end of the EMT, a sleeve outer surface; a
-6-
CA 02428898 2003-05-14
first sleeve end; and at least one of the corresponding barbs on the sleeve
inner
surface at or near the first sleeve end. The EMT joint assembly is preferably
constructed as discussed above.
In another aspect, the invention is a method of connecting EMT. When
used to connect cut EMT or EMT manufactured without indentations at its ends,
the method comprises: providing an EMT having an inner surface forming an
EMT cavity, an EMT outer surface, and an EMT first end; providing a sleeve
device having a sleeve inner surface farming a sleeve cavity adapted to
receive
the EMT first end, a sleeve outer surface, a first sleeve end, and at least
one
barb on the sleeve inner surface at or near the fir:>t sleeve end; and
inserting the
EMT into the sleeve cavity.
When used to connect or couple EMT having at least one indentation in
the EMT outer surface at the EMT first end, the barb will engage the
indentation
when the EMT is inserted into the sleeve cavity. Preferably, a ground tab on
the
sleeve device will be bent inwardly to contact the EMT. Moreover, the
inventive
method can be used to connect the EMT and sleeve device to a junction box or
transition fitting through the use of a linking device, as described above.
The present invention significantly reduces the time required for
electricians and installers to connect EMT and addresses a serious safety
concern often raised regarding the installation of EMT. The present invention
eliminates the time-consuming complexity of the existing connection methods by
allowing the EMT to simply snap together while providing improved and more
reliable ground paths. The invention offers the installer the option of using
the
new labor saving fittings or to continue to use traditional fittings with no
loss in
installation time or performance. Moreover, the loss of interior wire fill
space will
be insignificant. The installed cost of the raceway system will be
significantly
reduced while, most importantly, the concerns of poor workmanship resulting in
poor ground path and potential safety hazards will be extremely reduced or
eliminated.
CA 02428898 2003-05-14
Brief Description of Drawings
Figure 1 is a side view of an embodiment of a length of EMT having D-
shaped indentations.
Figure 2 is a front view of the EMT of FIG. 1 along line II-II.
Figure 3 is a perspective view of a portion of the EMT of FIG. 1.
Figure 4 is a side view of an end portion of an EMT having linearly-shaped
indentations.
Figure 5 is a is a side view of an embodiment of a sleeve coupling
according to the present invention.
Figure 6 is a front view of the sleeve coupling of FIG. 5 along line VI-VI.
Figure 7 is a perspective view of a portion of the sleeve coupling of FIG. 5.
Figure 8 is a side view of an embodiment of a linking device adapted to
connect a length of EMT to a junction box according to the present invention.
Figure 9 is a front view of the linking device of FIG. 8 along line IX-IX.
Figure 10 is a perspective view of the linking device of FIG. 8.
Figure 11 is a side view of an embodiment of a linking device adapted to
connect two lengths of EMT according to the present invention.
Figure 12 is a side view of an embodiment of a connection assembly
comprising the linking device of FIG. 8 and a sleeve half.
Figure 13 is a front view of the connection assembly of FIG. 12 along line
XIII-XIII.
Figure 14 is a side view of an embodiment of an EMT joint assembly
comprising the sleeve coupling of FIG. 5 connecting two lengths of the EMT of
FIG. 1.
_g_
CA 02428898 2003-05-14
Modes for Carrying Out the Invention
Referring to FIGS. 1-3, an embodiment of a length of EMT is illustrated
according to the present invention. EMT 10 has tubular shape and a circular
cross-sectional profile. EMT 10 can be constructed of steel, alloys, aluminum,
or
any other metal or material capable of carrying electricity. EMT 10 has an
outer
surface 13 and an inner surface 14. EMT 10 has EMT first end 11 and EMT
second end 12. Inner surface 14 farms EMT cavity 15 extending through the
length of EMT 10 for holding wire.
EMT 10 further comprises indentations, in the form of D-shaped dimples
16, at both EMT first end 11 and EMT second end 12. Each of the D-shaped
dimples 16 are adapted to receive and engage a corresponding barb 25 of
sleeve device 20 (FIGS. 6 and 7). EMT 10 comprises four D-shaped dimples 16
circumferentially located around each of its ends 11, 12., D-shaped dimples 16
are formed in outer surface 13 by punching or pressing and preferably have a
depth of approximately one-eighth inch. EMT 10 is one and one-half inch EMT
pipe (i.e. one and one-half inch diameter) but can take on any size and still
be
within the scope of the present invention.
D-shaped-dimples 16 are located a distance A from EMT first and second
ends 11, 12. Distance A is substantially equal to distance B, the distance
that
barbs 25 are located from first and second sleeve ends 21, 22 (FIG. 5). D-
shaped dimples 16 also correspond to the circumferential arientation of barbs
25
on sleeve coupling 20 (F1G. 5).
Referring now to FIG. 4, EMT 17 is illustrated according to a second
embodiment of the present invention. in this alternative embodiment, EMT 17
has four linearly shaped grooves 18 in outer surface 13 instead of the ~-
shaped
dimples 16. Similar to D-shaped dimples 16, linearly shaped grooves 18 are
adapted to receive and engage a corresponding barb 25 of sleeve coupling 20
(FIGS. 6 and 7). While two examples of the indentation on outer surface 13
have been illustrated, those skilled in the art will appreciate that the
-9-
CA 02428898 2003-05-14
indentations) can take on almost any shape or sire, including a roll groove
that
extends around the entire circumference of outer surface 13.
FIGS. 5-7 illustrate an embodiment of a sleeve coupling according to the
present invention. Sleeve coupling 20 is designed to be used to connect two
lengths of EMT 10 (as shown in FIG. 14). However, those skilled in the art
will
appreciate that sleeve coupling 20 can be modified to be a connector, which
can
be used a single length of EMT to a junction box or any type f transition
fitting.
Sleeve coupling 20 comprises a first sleeve end 21 and a second sleeve
end 22. Sleeve device 20 is constructed of spring steel and has a C-shaped
cross sectional profile (visible in FIG. 6). The C-shaped cross-sectional
profile
and the steel spring construction allow sleeve coupling 20 to be easily fitted
around EMT 10 (FIG. 14) without damaging barbs 25. Sfeeve coupling 20 has
an inner sleeve surface 23 and an outer sleeve surface 24. Inner sleeve
surface
23 forms sleeve cavity 26, which extends the length of sleeve coupling 20.
Sleeve cavity 26 is sized and shaped so as to be capable of receiving one of
the
EMT ends 11 or 12 of EMT 10 (FIG. 1 ). Sleeve coupling 20 preferably
comprises a middle inner ridge 27 on inner sleeve surface 23 near the center
of
sleeve coupling 20. Middle inner ridge 27 acts a "stop" for EMT that is
inserted
into sleeve cavity 26.
Sleeve coupling 20 further comprises four barbs 25 at each of its sleeve
ends 21, 22. The barb arrangement on second sleeve end 22 is the same as the
barb arrangement on first sleeve end 21. Barbs 25 are formed by punching or
pressing the steel and bending the barbs inward and back. Optionally, the
steel
will be heat tempered thereafter. Barbs 25 are designed to slide over the EMT
outer surface 13 and "snap" into corresponding D-shaped dimples 16 {FIG. 1 ).
Preferably, the barbs will point down and slightly back and will "capture" or
"contact" the flat part of the D-shaped dimple 16 (FIG. 1 ).
Sleeve coupling 20 also has ground tab 28. Ground tab 28 is formed by a
punched or pressed slot. Ground tab can 28 can be bent inward along dotted
-10-
CA 02428898 2003-05-14
line 29 so that ground tab 28 will contact EMT outer surface 13 when EMT 10 is
positioned in sleeve cavity 26 (as illustrated in FIG. 14). This helps to
enhance
the current carrying capability and helps to maintain electrical continuity
throughout the system.
Sleeve coupling 20 further comprises set screw hole 30 having set screw
31 threadily engaged therethrough. Set screw 31 is preferably a hex-shaped
screw. This set screw feature allows sleeve device 20 to be used in
conjunction
with cut EMT or EMT manufactured without indentations at its ends. This allows
maximum flexibility and eliminates the need for the field mechanic to carry
two
types of couplingslconnectors.
Sleeve coupling 20 can be modified to be a connector to be used to
connect a length of EMT to a junction box or other transition fitting. In the
connector embodiment, the second sleeve end wall be adapted to connect to a
junction box or other transition fitting by modifying the outer sleeve surface
near
the second sleeve end to be threaded or by incorporating a snap fit assembly.
In
this embodiment, the second sleeve section will be solid and be constructed
similar to second link section 42 shown in Figure 8.
Referring now to FIGS. 8-10, linking connector 40 is illustrated. Linking
connector 40 has first section 41 and second section 42. First section 41 and
second section 42 are separated by hex-shaped separator 43. Separator 43 not
only acts to separate sections 41 and 42 but can also be used to turn linking
connector 40 if necessary.
First section 41 has a link outer surface 44 and a fink inner surface 45.
Link inner surface 45 forms link cavity 46. Link cavity 46 is sized and shaped
to
receive one of end 11, 12 of EMT 10. First section 41 further comprises four
barb access holes 47 and two ground tab holes 48. Barb access holes 47 are
sized and positioned on first link section 41 so as to allow a corresponding
barb
25 of sleeve half 60 to extend therethrough when :sleeve half 60 is fitted
around
first link section 41, as shown in FIGS. 12 and 13. Similarly, ground tab
holes 48
-11-
CA 02428898 2003-05-14
are positioned and sized to allow a corresponding ground tab 28 of sleeve half
60 to extend therethrough when the sleeve half 60 is fitted around first link
section 41, as shown in FIGS. 12 and 13. First section 41 also has set screw
hole 49. Set screw hole 49 is adapted to allow set screw 50 to extend
therethrough (FIG. 12). Set screw 50 is preferably a hex-shaped screw.
Alternatively, set screw hole 49 can be a threaded hole so as to threadily
engage
set screw 50. When set screw hole 49 is threaded, is not necessary that set
screw hole 30 on half sleeve 60 be threaded (FIG. 12).
Finally, linking connector 40 comprises a first link end 51 and a second
link end 52. First section 41 preferably has outer ridge 53 circumferentially
located on outside surface 44 at or near first link end 51. Outer ridge 53
helps
ensure that sleeve half 50 is properly positioned on first section 41 when it
is
fitted around linking connector 40, as illustrated in FIG. 12.
Second section 42 of linking connector 40 is adapted to engage a junction
box or other transition fitting (not illustrated). This is done by threading
outside
surface 54. Alternatively, a snap fit assembly or any other connection means
can be incorporated into second section 42.
It is possible to adapt the linking connector concept described above to be
a coupling used to connect two lengths of EMT. Referring now to FIG. 11, link
coupling 70 is illustrated. As with linking connector 40, link coupling 70
comprises a first section 71 and a second section 72. Link coupling 70 also
comprises hex-shaped separator 73. First section 71 is designed similar to
first
section 41 of linking connector 40, comprising barb access holes 77, ground
holes 78, and set screw hole 79. However second section 72 is also designed to
engage one of the ends 11 or 12 of a second length of EMT 10. This is done by
making second section 72 a mirror image of first section 71. As such, second
section 72 is also adapted to have a half sleeve 60 fitted around it.
Referring now to FIGS 12 and 13, connection assembly 80 is illustrated.
Connection assembly 80 comprises linking connector 40 and half sleeve 60.
-12-
CA 02428898 2003-05-14
Linking connector 40 is described in detail above in relation to FIGS. 8-10.
Half
sleeve 60 is one half of sleeve connector 20, which is described in detail
above.
As such, a detailed explanation of the structure of these components will be
omitted. Only the structural cooperation between half sleeve 60 and linking
connector 40, when fitted together, will be discussed.
Half sleeve 60 has a C-shaped cross-sectional profile and is made of
spring steel. Half sleeve 60 is sized and shaped so that it fits around first
section
41 (FIG. 8) of linking connector 40. Outer ridge 53 helps ensure that half
sleeve
60 is properly positioned. When half sleeve 60 is fitted around first section
41
(FIG. 8), the four barbs 25 of half sleeve 60 extend through corresponding
barb
access holes 47 of linking connector 40 (best visible in FIG. 13). As such, an
end 11, 12 of EMT 10 (FIG. 1 ) can be inserted into link cavity 46 so that the
barbs 25 will engage corresponding dimples 16 (FIG. 1 ).
Set screw hole 49 of linking connector 40 is substantially aligned with set
screw hole 30 of half sleeve 60. Set screw 50 can then be extended through
and threadily engage both set screw holes 49 and 30. When an end 11, 12 of
EMT 10 (FIG. 1 ) is inserted into link cavity 46 and set screw 50 is
incorporated,
set screw 50 will contact the outer surface 13 of EMT 10 (FIG.1 ). This will
help
form a ground path and secure the EMT 10 in place. As discussed earlier, the
use of a set screw is not necessary and is preferably only used when the EMT
end does not have indentations.
Additionally, ground tab holes 48 of linking connector 40 are substantially
aligned with ground tabs 28 of half sleeve 60. Ground tabs 28 can be bent
inward to extend through ground tab holes 48. When an end 11, 12 of EMT 10
(FIG. 1 ) is inserted into link cavity 46 and ground tabs 28 are bent inward,
ground tabs 28 will contact the outer surface 13 of EMT 10 (FIG.1 ).
Referring now to FIG. 14, EMT joint assembly 90 is illustrated. EMT joint
assembly 90 comprises sleeve coupling 20 operably coupled with and
connecting two lengths of EMT 10. The structure of sleeve coupling 20 and EMT
-13-
CA 02428898 2003-05-14
are discussed in detail above. When sleeve coupling 20 is used to couple
two lengths of EMT 10, one of the ends 11, 12 of each EMT 10 is inserted into
sleeve cavity 46 from opposite sides until they butt against inner ridge 27
(FIGS.
5-7)
5 When fully inserted into sleeve coupling 20, barbs 25 engage
corresponding dimples 16 of EMTs 10, locking them in place. Set screws 31 are
tightened so as to contact the EMTs 10. The use of a set screw is not
necessary
and is preferably only used when the EMT end does not have indentations.
Ground tabs 28 are either bent inward so as to contact the EMTs 10 or can be
10 pre-bent.
Alternatively, sleeve coupling 20 can be used to couple EMTs that do not
have indentations or dimples. Additionally, if sleeve coupling 20 is replaced
by
connection assembly 80 (FIG. 12), a single length of EMT 10 can be connected
to a junction box or other transition fitting.
While the invention has been described and illustrated in sufficient detail
that those skilled in this art can readily make and use it, various
alternatives,
modifications, and improvements should become readily apparent without
departing from the spirit and scope of the invention.
_l~._
