Electric power distribution track

An improved electric power distribution track comprises a metal-reinforced duct and at least three conductors extending along the length thereof. The duct is shaped to have a top wall, a pair of lateral sidewalls and a lengthwise bottom opening, and is composed of a correspondingly shaped metal-made core channel member covered by an insulation sheath of a plastic material. Three conductors are disposed on the inner sheath in a trigonous arrangement with one of the conductors on the top wall and the two others on the opposite sidewalls. Integrally projecting from the corresponding portions of the inner sheath are support members for holding the respective conductors at positions spaced inwardly from the inner periphery of the sheath. The support member on the top wall is connected to those on each of the sidewalls by a connection rib integrally extending therebetween for reinforcing the support members by one another to thereby retain the conductors held thereby in positions. Each connection rib extends between the adjacent ones of the support members in a non-linear manner.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to an electric power distribution track 
for various power consuming loads such as lighting fixtures and other 
electric devices, and more particularly to an electric power distribution 
track of the type comprising a metal-reinforced plastic duct and at least 
three conductors which extend along the length of the duct at positions 
spaced inwardly from the inner periphery of the plastic duct and are held 
by respective supporting members integrally projecting on the top wall and 
the opposite sidewalls to form a trigonous arrangement of the conductors 
at any cross section of the duct. 
2. Related Prior Art 
Electric power distribution tracks having a metal-reinforced plastic duct 
are known, for example, as disclosed in U.S. Pat. No. 3,704,437, which 
comprises a metal-reinforced plastic section which carries several 
electric conductors on its inner periphery of the plastic duct. However, 
there is no provision of holding the conductors on the top wall and the 
opposite sidewalls of the plastic duct respectively by support members 
projecting inwardly from the insulation sheath of the duct. 
In the meanwhile, the above trigonous arrangement of the conductors is 
advantageous in that the three conductors can be selectively utilized as 
forming a three-phase current distribution circuit or as forming two 
independent circuits carrying a single-phase three-wire current. Apart 
from the above, it is preferable for the metal-reinforced plastic duct 
including a metal core covered by an insulation sheath of the plastic 
material to separate the conductors from the metal core by a distance 
great enough to prevent accidental shorting therebetween due to possible 
defect or breakage of the insulation sheath as well as to elongate as much 
as possible the creepage distance of insulation at an exposed end face of 
the track. 
To these ends, it may be reasonable to integrally project the supporting 
members holding the respective conductors in spaced relation from the 
inner periphery of the duct, or from the top wall and the sidewalls. 
However, this attempt certainly induces another problem that increasing 
the amount of projection of the support member results in the loss of 
rigidity of the support member and therefore the support member as well as 
the conductor held thereby become unstable to such an extent that proper 
contacting engagement is no more expected between the conductor and a 
cooperative terminal blade of an adaptor plug through which the electric 
device derives the power from the track, in addition to that, misalignment 
occurs between the conductors of the adjacent tracks at the time of 
coupling the lengths of the tracks. 
One solution to the above is thought to provide suitable ribs each 
integrally bridging between the support member on the top wall and that on 
each of the sidewalls within the confines of the track for joining the 
three support members into a consolidated unit. But, there still remains a 
further problem in this scheme that the rib of a certain configuration, 
for example, the one extending straight will result in excess reinforcing 
effect to permanently retain the three support members in a fixed 
trigonous relationship even if the duct or track be subjected to such an 
external force to spread outwardly the sidewalls and the support member 
thereon as might be seen at the time of dropping the track onto the floor. 
This may adversely cause the unacceptable separation of the inner sheath 
at the top wall, from the core member to which it has been adhered, since 
the consolidated unit of three support members would act as a rigid 
construction member absorbing substantially no stress attendant with the 
above external force and consequently pull the insulation sheath of the 
top wall downwardly as the sidewalls and the support member thereon are 
forced to be deformed outwardly in a spreading manner. Such separation of 
the insulation would lead to the breakage of the insulation sheath and 
therefore should be unacceptable from the view point of providing an 
electrically safe track of practical utility. 
3. Related Applications 
A related application is application Ser. No. 694,852 filed Jan. 25, 1985 
by the same applicants entitled "Electric Power Distribution Track" now 
abandoned. 
SUMMARY OF THE INVENTION 
The present invention has been devised with a view to overcoming the above 
problems and presenting an improved electric power distribution track. The 
track comprises an elongated metal-reinforced plastic duct and a plurality 
of electrically isolated conductors extending along the length thereof at 
positions spaced inwardly from the inner periphery of the duct. The duct 
is outlined to have the cross section of a generally downwardly disposed 
U-shape with a top wall, a pair of lateral sidewalls, and a lengthwise 
bottom opening, said duct including a correspondingly shaped metal-made 
core channel member covered by an insulation sheath of an electrically 
insulative plastic material. One of the conductors is supported on the top 
wall and at least one conductor is supported on each of the opposite 
sidewalls by respective support members integrally projecting from the 
inner sheath at corresponding walls so that three of the conductors are 
disposed in a trigonous arrangement at any cross section of the track. 
Each of the support members projects inwardly from the sheath of the duct 
and holds the complementary conductor at its inner end portion so as to 
leave between the core channel member and the conductor a distance great 
enough to assure proper electric insulation against possible defect or 
breakage of the insulation sheath and at the same time to elongate the 
creepage distance of insulation at the exposed end face of the track. 
Connecting the support member on the top wall to the adjacent support 
member on each of the opposite sidewalls is a connection rib which 
integrally extends therebetween in a non-linear manner such that the 
connection rib is permitted to resiliently stretch in the direction of 
becoming linear when the track is subjected to such an external force to 
deformingly spread the sidewalls outward. With this arrangement of 
integrally connecting the adjacent ones of the support members by the 
respective connection ribs of non-linear configuration, the support 
members can be reinforced by each other to form a consolidated unit which 
is tough enough for stably sustaining the individual conductors in 
positions but allows the connection ribs to resiliently spread or deform 
for absorbing the stress applied thereto when the track is subjected to 
the external force of spreading outwardly the sidewalls. Thus, the support 
members on the opposite sidewalls can deform together with the spreading 
sidewalls to a limited extent without giving any deformative forces to the 
remaining support member on the top wall and therefore without pulling 
that support member and the adjacent portion of the insulation sheath 
downwardly in the direction of separating the insulation sheath from the 
core member, eliminating the possibility of separating the insulation 
sheath integrally carrying that support member from the metal core member. 
Accordingly, it is a primary object of the present invention to provide an 
electric power distribution track which is capable of supporting the 
conductors stably in positions by respective support members integrally 
projecting inwardly from the plastic insulation sheath covering the metal 
core member, yet preventing the separation of the insulation sheath from 
the core member and therefore giving rise to a tough and electrically safe 
track construction of practical utility. 
In preferred forms, said connection ribs are configured into simple but 
advantageous shapes for assuring the above-mentioned effects, one having 
the cross section comprises two straight segments integrally extending 
from each of the adjacent ones of the support members and interconnected 
by an oblique segment angularly displaced therefrom, and the other 
comprising an arcuate segment integrally extending between the adjacent 
ones of the support members. 
Each of said conductors is configured into an elongated hollow member with 
an annular cross section. Thus, the connection between the conductors of 
the adjacent tracks can be made simply by inserting the opposite ends of 
connection pins into corresponding holes in the longitudinal ends of the 
hollow members of the adjacent tracks, at which connection, the inner 
periphery of each hollow member can serve as an enlarged contacting 
surface sufficient for electrical connection between the longitudinally 
adjacent conductors. In addition to the above, the holes in the hollow 
members cooperate with the connection pins to bring the conductors in 
exact longitudinal alignment with each other between longitudinally 
adjacent tracks. Each of of the support members is formed at its inner end 
portion with a rail of C-shaped cross section with an inwardly oriented 
slit for firmly receiving therein each conductor, the conductor being 
exposed to the inside of the duct through the slit so as to define thereat 
a contacting surface for electrical connection with a destined electric 
device. 
It is therefore another object of the present invention to provide an 
electric power distribution track of which conductors can be easily and 
securely connected to each other between the adjacent tracks, and in which 
the conductors can be easily and firmly held by the respective support 
members. 
Each of the C-shaped rails receiving the conductors joins integrally the 
insulation sheath through a stem projecting inwardly from the inner 
surface of the sheath at the respective portions on the top wall and the 
opposite sidewalls so that the rail is spaced inwardly therefrom by the 
length of the stem. At the longitudinal or end face portions of the track, 
each stem is notched to define thereat a recess which serves to further 
elongate the creepage distance of insulation between the metal core 
channel member and each of the conductors. With this provision of the 
recess in each of the stems integrally interconnecting each rail and the 
insulation sheath, the spacing between the metal core member and the 
conductors can be reduced to a minimum while assuring enough creepage 
distance of insulation, which gives rise to a compact construction of the 
track. 
It is therefore a still further object of the present invention to provide 
an electric power distribution track which can be made compact, yet assure 
sufficient creepage distance of insulation at the end face portion of the 
track. 
The present invention discloses a further advantageous feature in which a 
pair of auxiliary conductors are incorporated to extend along the length 
of the track at positions downwardly displaced from said conductors 
adjacent the bottom opening of the track as being supported by respective 
support members also integral with said sheath. These auxiliary conductors 
are sized to have a smaller cross sectional area than that of said 
conductors such that the auxiliary conductors form a power distribution 
circuit of smaller current-carrying capacity while said conductors are 
cooperative to form a power distribution circuit of larger 
current-carrying capacity. Consequently, the track can have two 
independent circuits of different current-carrying capacities, whereby 
allowing the connection of electric devices of different power or current 
requirements to the single track. 
It is therefore a still further object of the present invention to provide 
an electric power distribution track which can be conveniently utilized as 
supplying power to electric devices of different current requirements. 
These and other objects and advantageous features of the present invention 
will be apparent from the following detailed description of the preferred 
embodiments when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1 to 3, there is illustrated an electric power 
distribution track in accordance with a first preferred embodiment of the 
present invention. The track is designed to include three lines of main 
conductors 12 and additionally a pair of auxiliary conductors 11 of a 
cross section smaller than that of the main conductor 12. The main 
conductors 12 are cooperative to form one or two main power distribution 
circuits of a larger current capacity, that is, one circuit for a 
three-phase current or two independent circuits for a single-phase 
three-wire current. Likewise, the auxiliary conductors 11 are cooperative 
to form an auxiliary power distribution circuit of a small 
current-carrying capacity. These circuits of different current-carrying 
capacities are selectively utilized as feeding the power to several 
electric devices depending upon the power or current requirements thereof. 
For example, the power distribution circuit of larger current-carrying 
capacity provides for 300 volts, 100 amps suitable for driving commercial 
motors in machine tools and the like, and the power distribution circuit 
of smaller current-carrying capacity provides for 250 volts, 30 amps 
suitable for driving lighting fixtures of a relatively small current 
requirement. The latter circuit may be utilized for passing remote control 
signal, as necessary to provide a remote control operation with respect to 
one or more electric devices coupled to the track. 
The track comprises a metal-reinforced plastic duct 1 shaped to have a 
generally downwardly disposed U-shaped cross section, more precisely, a 
rather hexagonal cross section with one bottom side of the hexagon removed 
to define thereat a lengthwise bottom opening 2 and with a pair of 
sidewalls 3 depending from the opposite ends of a top wall 4, each 
sidewall 3 composed of two adjacent angularly disposed sides of the 
hexagon. Formed respectively at the lower ends of the sidewalls 3 are 
inturned flanges 5 which project toward each other to leave therebetween 
said bottom opening 2. The duct 1 further comprises a correspondingly 
shaped aluminium-made core channel member 6 fully covered except at the 
portions on the upper surface of the flanges 5 by an insulation sheath 7 
of an electrically insulative plastic material such as vinyl chloride, 
polypropylene and the like. Thus, the insulation sheath 7 is formed on the 
inner and outer surfaces of the duct 1 with only an exception that the 
core channel member 6 is exposed at the respective portions on the flanges 
5 to define thereat earthing surfaces 8. In this sense, the core channel 
member 6 serves as an earthing conductor for the electric devices to be 
coupled to the track. Said core channel member 6 is inserted in the 
insulation sheath 7 at the time of molding the sheath 7 to provide an 
intimate and overall adhereing connection between the core channel member 
6 and the sheath 7. The insulation sheath 7 on the outer surface of the 
duct 1 is horizontally knurled for providing secure grip by a person 
handling the track. 
Three main conductors 12 extend along the entire length of the duct 1 in 
spaced and parallel relation with one another at positions upwardly or 
inwardly of the duct 1 with one of the conductors 12 located on the top 
wall 4 and the two others respectively on the sidewalls 3 so that the main 
conductors 12 are disposed in a trigonous arrangement at any cross section 
of the duct 1. Integrally projecting from the inner sheath 7 of the duct 1 
at the portions corresponding to the main conductors 12 are main support 
members 14 for holding the main conductors 12, respectively. Each of the 
main conductors 12 is in the form of an elongated hollow member with an 
annular cross section the area of which is much larger than that of the 
auxiliary conductor 11. Each main support member 14 comprises a rail 20 
which is C-shaped in cross section with an inwardly oriented slit 21 and 
is connected integrally to the sheath 7 through a stem 22 extending from 
the periphery of the rail 20 at the portion diametrically opposed to the 
slit 21. Each of the main conductors 12 is fitted within each of the 
C-shaped rails 20 with the portion along the periphery thereof being 
exposed to the inside of the duct 1 through the slit 21 to define at a 
contacting surface for electrical connection with the electric device. The 
contacting surface of the main conductor 12 on each sidewall 3 is arranged 
substantially in vertical alignment with that of the auxiliary conductor 
11 on the same side for assuring convenient access both for the main and 
auxiliary conductors. 
Said auxiliary conductors 11 each being in the form of a solid strip with a 
rectangular cross section extend likewise along the entire length of the 
duct 1 in spaced and parallel relation with each other adjacent the bottom 
opening 2 and held by respective auxiliary support members 13 integrally 
projecting inwardly from the insulation sheath 7 on the sidewalls 3. As 
best shown in FIG. 2, each auxiliary support member 13 is H-shaped in 
cross section with a pair of horizontal legs 15 extending from the sheath 
7 and connected by a web 16, the web 16 being offset to a vertical center 
axis of the duct 1 to be cooperative with the inner end portions of the 
legs 15 to define a recess for receiving therein the auxiliary conductor 
11. The legs 15 of the auxiliary support member 13 on each sidewall 3 
terminate at a point just upwardly of the innermost end of the 
corresponding flange 5 on the same sidewall 3 and are formed at their free 
end portions with barbs 17 for secure positioning of the auxiliary 
conductor 11 within the recess. 
The stem 22 of the main support members 14 belonging to each sidewall 3 
projects from the vertex 23 of said two angularly disposed sides of the 
hexagon defining each one of the sidewalls 3 in such a way as to afford 
inside of the corner formed between said angularly disposed sides of the 
hexagon enough space for the main conductor 12 having a larger transverse 
dimension or diameter than that of the auxiliary conductor 11. In other 
words, the transverse distance M between the sidewall 3 and the contacting 
surface of the main conductor 12 located thereon can be set to be longer 
than the transverse distance A between the sidewall 3 and that of the 
auxiliary conductor 11 located thereon, since the auxiliary support member 
13 extends horizontally from the sidewall 3 at the portion inwardly 
displaced from the vertex 23. This construction can successfully reduce 
the amount of projection of the auxiliary support member 13 to an extent 
that the member 13 will not become unstable while keeping the contacting 
surface of the auxiliary conductor 11 substantially in vertical alignment 
with that of the main conductor 12 on the same side. Without such 
reduction in the amount of projection of the auxiliary support member 11, 
or if the sidewall be made vertically flat to have the root portions of 
the main and auxiliary support members 14 and 13 on the same vertical 
plane, the auxiliary support member 13 would have to require extra 
transverse dimension to the above distance A, becoming more unstable due 
to the increased elasticity of the member resulting from the added amount 
of projection. Consequently, the above construction is advantageous for 
stably supporting the auxiliary conductors 11 of less horizontal dimension 
than that of the main conductors 12 in downwardly displaced relationship 
from the latter, while arranging the contact surfaces of the main and 
auxiliary conductors 12 and 11 on the same side in substantially vertical 
alignment with each other. 
Integrally bridging between the main support member 14 on the top wall 4 
and the main support member 14 on each of the sidewalls 3 is a connection 
rib 25 which blends at its ends into peripheries of the adjacent ones of 
the main support members 14. The connection ribs 25 thus join the members 
14 into a consolidated unit for being reinforced by one another so as to 
stably hold the individual members 14 and the main conductors 12 in 
positions. With the results of the above, the main and auxiliary 12 and 11 
integrally projecting from the insulation sheath 7 can be formed to be 
less susceptible to fluctuations to thereby hold the corresponding 
conductors in proper positions, assuring easy and correct coupling thereof 
between two lengths of the tracks. 
Each of said connection ribs 25 comprises a pair of straight segments 26 
which project integrally from the peripheries of the C-shaped main support 
members 14 in a direction normal thereto and are integrally connected by 
an oblique segment 27 so as to provide a composite cross section of 
non-linear shape or of generally L-shape with a beveled corner 
intermediate its length. The above non-linear configuration can provide 
additional resiliency to the connection ribs 25 so that they are permitted 
to resiliently spread outwardly in the direction of approaching a straight 
line while retaining the effect of reinforcing the main support members 14 
by one another. Thus, if the track of the present invention should be 
subjected to such an external force as to deformingly spread the sidewalls 
3 together with the main support members 14 formed thereon, the attendant 
stresses applied to the connection ribs 25 can be well absorbed by the 
ribs 25 themselves and will not act further upon the remaining main 
support member 14 on the top wall 4, whereby the main support member 14 on 
the top wall 4 can be retained in position and protected from being pulled 
downwardly in the direction of separating the inner sheath 7 integrally 
formed therewith from the core channel member 6. Such separation of the 
sheath 7 would lead to the breakage of the sheath 7 and should be 
eliminated from the viewpoint of providing electrically safe power track 
of practical utility. 
The track thus constructed can be secured to a ceiling by means of hangers 
28 and provides a base for mechanically and electrically connecting the 
various electric devices of different current requirements. For this 
purpose, two types of adaptor plugs 30A and 30B are employed for feeding 
powers from the circuits of different current-carrying capacities 
respectively to the destined devices depending upon the current 
requirements of the devices, larger or smaller. As shown in FIGS. 3A and 
3B, each of the adaptor plugs 30A and 30B is provided at its top with a 
terminal head 33 from which a pair of horizontal wings 34 extend in 
opposite directions. The terminal head 33 has an upright vertical axis to 
be centered with the center axis of the track about which it is rotated 
90.degree. for engagement of the wings 34 with the respective inturned 
flanges 5, at which engagement said earthing surface 8 is in contact with 
a ground terminal (not shown) provided on either of the wings 34 leading 
to the grounded side of the electric device. The adaptor plug 30A is for 
coupling the circuit of smaller current-carrying capacity to the destined 
device and has a pair of auxiliary terminal blades 31 which project 
horizontally outwardly from the terminal head 33 in parallel relation with 
the wings 34 at positions spaced upwardly therefrom by a short distance to 
be in contacting engagement respectively with the auxiliary conductors 11, 
as shown in FIG. 3A. The adaptor plug 30B is for coupling the circuit of 
larger current-carrying capacity to the destined device and has three main 
terminal blades 32, one projecting upwardly from the terminal head 33 in 
alignment with the center axis thereof for contacting engagement with the 
main conductor 12 on the top wall 4 and two others projecting horizontally 
outwardly from the same in parallel relation with wings 5 at positions 
spaced upwardly therefrom by a long distance for contacting engagement 
respectively with the main conductors 12 on the opposite sidewalls 3 of 
the duct 1. The adaptor plug 30B shown in FIG. 1 is of the type 
incorporating a circuit breaker for the particular electric device, such 
as the electric motor and the like of larger current requirements. The 
adaptor plugs 30A and 30B can be positioned at any convenient location 
along the length of the track by the slidable engagement of the wings 34 
with the inturned flanges 5 of the duct 1 and the exposed bottom opening 2 
is preferably closed by a cover plate 9 to be cut to a suitable length, 
the opposite sides of which are inserted within respective grooves formed 
between the auxiliary support members 13 and the inturned flanges 5 so as 
to rest on the latter. 
FIG. 4 shows a modification of the above first embodiment which is similar 
in construction thereto except for the particular configuration of the 
connection rib 25. In this modification, each connection rib 25 blends at 
its ends into the stems 22 of the main support members 22, and not into 
the C-shaped rails 20 as in the first embodiment. The stress absorbing 
effect of the connection ribs 25 of course remains effective in this 
modification. 
Referring to FIG. 5, there is shown a second preferred embodiment of the 
present invention, in which are included only main conductors 52 of the 
same construction as in the above first embodiment. The track of this 
embodiment comprises a duct 41 of a generally rectangular cross section 
having a top wall 44, opposite sidewalls 43, and a lengthwise bottom 
opening 42. Provided at the lower ends of the sidewalls 43 are inturned 
flanges 45 which project toward each other to define therebetween said 
bottom opening 43. Likewise in the first embodiment, the duct 41 is 
composed of a correspondingly shaped metal-made core channel member 46 
covered by an insulation sheath 47 of a suitable plastic material. Support 
members 54 for the respective conductors 52 integrally project from the 
inner surface of the insulation sheath 47 at positions respectively on the 
opposite sidewalls 43 and the top wall 44, each support member 54 
comprising a C-shaped rail 60 with an inwardly oriented slit 61 and a stem 
62 extending from the periphery of the rail 60 at the position 
diametrically opposed to the slit 61 and joining the insulation sheath 47 
at right angle thereto. Thus, the conductors 52 are received within the 
respective rails 50 each with the portion of the periphery being exposed 
to the inside of the duct 41 through the slit 61 so as to define thereat a 
contact surface for electrical connection with the terminal blade of an 
adaptor plug of the like construction as in the previous embodiment. Also 
in this embodiment, the support member 54 on the top wall 4 is integrally 
connected to the support member 54 on each of the sidewalls 43 by a 
connection rib 65 of the identical configuration to that shown in the 
first embodiment. 
At the longitudinal end or end face portions of the duct 41, each stem 62 
is notched to a certain depth, as best shown in FIGS. 6 and 7, so as to 
define thereat a recess 64, by which the creepage distance of insulation 
between the corresponding conductor 52 and the metal core channel member 
46 is further elongated. This is advantageous in reducing the amount of 
inward projection of each support member 54 to a minimum, while providing 
enough creepage distance of insulation at the end face portions of the 
track, which gives rise to a compact construction of the track of the type 
having the conductors held by the supporting members integrally projecting 
from the insulation sheath of the duct. 
Interconnection between the conductors 52 of the lengths of adjacently 
disposed tracks can be made by the use of a corresponding number of 
connection pins 70 each having a stop ring 71 intermediate its ends and 
defining at portions both sides thereof insertion split ends 72. The 
insertion split ends 72 are forcibly inserted in the corresponding 
conductors 52 of the adjacent tracks until the stopper ring 71 abuts 
against the end faces of the conductors 52, as shown in FIGS. 8A and 8B. 
An insulation sleeve 73 of a generally triangular loop is interposed 
between the adjacent tracks with the portions on both sides thereof being 
inserted respectively in said recesses 64 at the opposed end portions of 
the adjacent track so that it is positioned within the circumference of 
the track in such a manner as to enclose the end portions of all the 
conductors 52 therein for insulatively separating them from the core 
channel members 46 at the connection of the track, thus ensuring 
electrical insulation at the connection of the track between each of the 
conductors 52 and the core channel member 46. 
Referring to FIGS. 9 and 10, there are shown respectively modifications of 
the second embodiment of FIG. 5 which are similar in construction thereto 
but have connection ribs of configurations somewhat different from that in 
the above embodiment. In the modification of FIG. 9, the connection rib 
65a is formed to have a L-shaped cross section composed of a pair of legs 
each joining the rail 60 of each one of the adjacent support members 54. 
In the modification of FIG. 10, the connection rib 65b is formed to have 
an arcuate cross section extending between the stems 62 of the adjacent 
support members 54. The ribs 65a and 65b thus formed are also of 
non-linear in cross section and therefore retain the above stress 
absorbing effect, as described with regard to the first embodiment.