Note: Descriptions are shown in the official language in which they were submitted.
HEATING CABLE
BACKGROUND OF THE TECHNOLOGY
The present technology relates generally to cables used in systems to
heat floors, walls and other surfaces.
BRIEF SUMMARY OF THE TECHNOLOGY
In accordance with one aspect of the invention, a cable is provided that
includes a first wire-shaped metal conductor (2), a second metal conductor (4)
extending a predetermined distance away from and parallel to the first
conductor
(2), and a matrix (3) made of a PTC material extending along the conductors
(2,
4), touching the latter and connecting them to one another electrically, with
temperature-dependent electrical resistance and a positive temperature
coefficient. At least one electrically insulating outer insulation layer (8)
surrounds
the conductors (2, 4) and the matrix annularly. At least a third and a fourth
metal
conductor (4) are provided which extend a predetermined distance away from
and parallel to the first conductor (2), touch the matrix (3) and are
connected
electrically by means of the latter to the first conductor (2), the second,
the third
and the fourth conductor (4) being made in a wire shape and, considering the
cross-section of the cable (1), being arranged distributed evenly over a
circular
track surrounding the first conductor (2).
In accordance with another aspect of the invention, a method of heating a
surface is provided, including: obtaining a cable, the cable having a first
metal
conductor, a second metal conductor extending a predetermined distance away
from and spirally laid relative to the first conductor, a matrix made of a PTC
material extending along the conductors, touching the latter and connecting
them
to one another electrically, with temperature-dependent electrical resistance
and
a positive temperature coefficient, and at least one electrically insulating
outer
insulation layer surrounding the conductors and the matrix annularly; and
installing the cable adjacent the surface.
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õ
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Figure 1 is a diagrammatic view of a cable according to a first embodiment
of the present invention and
Figure 2 is a diagrammatic view of a cable according to a second
embodiment of the present invention.
DETAILED DESCRIPTION OF THE TECHNOLOGY
The present invention relates to a cable comprising a first wire-shaped
metal conductor, a second metal conductor extending a predetermined distance
away from and parallel to the first conductor, a matrix made of a PTC
(Positive
Temperature Coefficient) material extending along the conductors, touching the
latter and connecting them to one another electrically, with temperature-
dependent electrical resistance and a positive temperature coefficient and at
least one electrically insulating outer insulation layer surrounding the
conductors
and the matrix annularly. Furthermore, the invention relates to a specific use
of
this type of cable.
A cable of the type specified at the start is described, for example, in DE
2015 217 979 Al, which is used to transmit energy as well as to provide
protection against over-current, over-voltage and over-heating. According to a
first embodiment the cable has an oval cross-section and comprises two wire-
like
metal conductors extending a pre-determined distance away from and parallel to
one another, a matrix produced from a PTC material with temperature-dependent
electrical resistance and a positive temperature coefficient embedding the two
conductors and an outer insulation layer surrounding and electrically
insulating
the matrix. The two conductors are separated from one another spatially and
are
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connected electrically to one another by means of the matrix so that a current
can flow between the conductors, the PTC material of the matrix conducting
electrical current better at low temperatures than at high temperatures. At
low
temperatures the cable can therefore conduct heat as well as a conventional
cable. However, as temperatures rise the conductivity is greatly reduced, by
means of which effective protection against over-current, over-voltage and
over-
heating is provided without separate protective devices being required for
this
purpose. According to a second embodiment the cable has a circular cross-
section and comprises a first wire-like, centrally positioned metal conductor,
a
matrix made of FTC material that embeds the first conductor, a second metal
conductor surrounding the matrix like a jacket (e.g., a metallic sheath or
metallic
wire braid or metallic wire grid) and contacting it, and an outer insulation
layer
surrounding the second conductor. Here too the two conductors are separated
from one another spatially and are connected electrically to one another by
means of the matrix so that a current can flow between them, the matrix acting
as a temperature-dependent resistor.
A disadvantage of the first embodiment of the cable described in DE 10
2015 217 979 Al is that this cable does not have a circular cross-section, and
for
some possible applications of the cable this is not desirable. A disadvantage
of
the second embodiment is that due to the fact that the second metal conductor
and the outer insulation layer may both have different thermal expansion
coefficients and elastic moduli than the matrix, said second metallic
conductor
may become detached from the matrix after repeated heating and cooling of the
cable, and this leads to the desired electrical connection between the second
conductor and the matrix worsening or being broken. Accordingly, correct
function of the cable in the long term cannot be guaranteed.
Proceeding from this prior art, an object of the present invention is to
devise a conductor of the type specified at the start with an alternative
structure
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= .
which at least partially eliminates the problems described above and/or
improves
the suitability of the cable for various applications.
In order to achieve this object the present invention devises a cable of the
type specified at the start which is characterised in that the second and at
least a
third and a fourth metal conductor are provided which extend a predetermined
distance away from the first conductor. The second, third and/or fourth
conductors can be parallel to the first conductor. In one embodiment, the
second, third and/or fourth conductors can be spirally laid around the first
conductor. The second, third and/or fourth conductors can make contact with
the
matrix and can be electrically connected by means of the latter to the first
conductor. The second, the third and the fourth conductor can be made in a
wire
shape and, considering the cross-section of the cable, can be arranged
distributed evenly over a circular track, e.g., spirally laid around the first
conductor. In other words, it is proposed to replace the second metal
conductor
made of a metallic sheath or metallic braid or grid described in the second
embodiment of DE 10 2015 217 979 Al with a number of wire-like conductors
which, considered in cross-section, are arranged distributed evenly around the
periphery of the first conductor, and apply an additional layer of preferably
a PTC
material over these wire-like conductors. The said additional layer of PTC
material can be crosslinked together with the inner layer of PTC material
surrounding the central metallic conductor, at a later stage in the process,
and
form a single, physically unitary matrix layer where the inner part and the
outer
part may have different conductivity versus temperature characteristics. The
advantage of this is that the metallic conductors surrounding the central
metallic
conductor, and the central metallic conductor itself, are now all within one
PTC
matrix, and maintain good contact with the PTC matrix irrespective of its
expansion and contraction during heating and cooling cycles.
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According to a first version of the present invention, all of the conductors
are fully embedded into a PTC material or matrix having a particular
conductivity
to temperature relationship or ratio.
According to a second version, the first conductor is fully embedded into a
PTC material or matrix having a particular conductivity to temperature
relationship or ratio, whereas the other conductors touch the said PTC
material
on its outer periphery and are coated with a covering layer which is made
separately from the PTC material and is integrally connected to the latter by
crosslinking, the covering layer possibly being made of a PTC material. At the
end of the processes, the final product can consist of a single layer of PTC
matrix, where the inner section between the central metallic conductor and the
surrounding outer metallic conductors has a specific conductivity to
temperature
relationship or ratio, and the outer section of the PTC matrix has a different
conductivity to temperature relationship or ratio, or none at all.
Both versions are characterised in that even after a very large number of
temperature cycles, very good contact is obtained between the matrix and the
conductors arranged on its outer periphery, by means of which correct function
of
the cable is ensured in the long term.
Preferably, the PTC material is a crosslinked plastic doped with carbon
particles. This type of plastic has proven to be particularly suitable.
Advantageously, a protective conductor with an annular cross-section is
provided which is disposed between an inner insulation layer surrounding the
matrix and/or the covering layer annularly and the outer insulation layer. By
providing this type of protective conductor acting as a ground shield, safety
is
increased.
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According to one embodiment the cable according to the invention has a
circular cross-section. Such a circular cross-section is very desirable for
many
applications.
Alternatively, the cable has a circular cross-section, wherein fillers or
ridges radially project from the outer surface of the outer insulation layer,
said
ridges being arranged in equal distances from each other along the
circumference of the cable jacket. Such ridges enlarge the outer diameter of
the
cable and enhance the gripping or clamping effect of the cable when arranged
at
napped cable carrier sheets, cable laying boards, concrete reinforcements and
the like.
The cable preferably has an outer diameter in the range of from 4 to 16
mm.
Furthermore, the present invention proposes the use of a cable as a
heating cable for surface heating in the form of floor, wall or ceiling
heating, the
cable having a first metal conductor, a second metal conductor extending a
predetermined distance away from and parallel to the first conductor, a matrix
made of a FTC material extending along the conductors, touching the latter and
connecting them to one another electrically, with temperature-dependent
electrical resistance and a positive temperature coefficient, and at least one
electrically insulating outer insulation layer surrounding the conductors and
the
matrix annularly. The use of this type of cable as a heating cable for surface
heating in the form of floor, wall or ceiling heating has the essential
advantage
that in areas in which the heat generated by the cable cannot be discharged
sufficiently, the heat cannot accumulate to such an extent that over-heating
of the
cable is caused, for example in areas of a floor heating system where a fixed
cabinet or fixed counter or low level furniture is located at that area. Up
until
now, such cables have not been used for said application because cables known
to date either have an external form which can only be laid in a meandering
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shape with difficulty or with a large construction height or, with an
appropriate
shape of the known cable, correct function could not be guaranteed in the long
term.
In the following same references denote same or similar components.
The cable 1 has a circular cross-section and comprises a centrally
positioned first wire-like metal conductor 2, in particular a copper
conductor,
which is embedded in a matrix 3 made of a PTC material with temperature-
dependent electrical resistance and a positive temperature coefficient. In the
present case the PTC material is a crosslinked plastic doped with carbon
particles, which touches the first conductor 2 peripherally. Furthermore, in
this
case the cable 1 comprises six additional wire-like metal conductors 4 which
each extend a predetermined distance away from and parallel to or spirally
laid
around the first conductor 2, as considered in cross-section are arranged
distributed evenly over a circular track surrounding the first conductor 2 and
touch the matrix 3 on its outer periphery. Accordingly, the additional
conductors
4 are electrically connected to the first conductor 2 by means of the matrix
3.
The additional conductors 4 are coated with a covering layer 5 which is formed
separately from the matrix 3 and are integrally connected to the latter in the
areas respectively between two additional conductors 4 by a crosslinking
process
performed on matrix 3 and layer 5. Accordingly, each additional conductor 4 is
embedded and integrated between the matrix 3 and the covering layer 5 which
are both crosslinked and crosslinked together, forming a single matrix layer
9. In
this case the covering layer 5 is produced from a different PTC material
having a
higher conductivity to temperature relationship than matrix 3 in order to
optimise
the electrical connection between all of the additional conductors 4.
Alternatively
however, a similar PTC material as matrix 3, or an electrically non-conductive
plastic may also be chosen for the covering layer 5. The covering layer 5 is
peripherally surrounded by an insulation layer 6 made of plastic which
insulates
electrically cable 1. Furthermore, a protective conductor 7 with an annular
cross-
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,
section is provided which in this case is formed by braided copper and is
surrounded by an electrically insulating outer insulation layer 8.
The cable 1 is particularly suitable for use as a heating cable for surface
heating in the form of floor, wall or ceiling heating. By virtue of its
circular cross-
section the cable 1 can easily be laid, in particular on cable laying boards
or
membranes, as disclosed for example in EP 3 006 835 Al, without having to lay
the cable 1 in any specific alignment. The same applies for clamping or fixing
the
cable 1 to screed carrier plates. By virtue of the arrangement according to
the
invention of the conductors 2 and 4 the outside diameter D of the cable 1 may
prove to be very small and preferably comes within the range of 4 to 16 mm so
that the surface heating only takes up a small construction height.
During operation a voltage is applied between the first conductor 2 and the
additional conductors 4 so that the current flows from the first conductor 2,
through the matrix 3, to the additional conductors 4 or vice versa. The matrix
3
heats up due to the flow of current, by means of which the desired heat output
is
provided. As the temperature increases the electrical conductivity of the PCT
material decreases so that a maximum heating temperature cannot be exceeded.
In areas where heat can only be discharged poorly, for example due to
furniture
that is positioned here, the decrease in conductivity may also take place
locally
so that a local accumulation of heat, and accordingly local over-heating of
the
cable, can be effectively counteracted.
Figure 2 shows a cable that essentially corresponds to the cable 1 shown
in figure 1. In addition, the cable 1 of figure 2 comprises fillers or
ridges10 radially
projecting from the outer surface of the cable jacket, such ridges 10 being
arranged in equal distances from each other along the circumference of the
cable
jacket. Such ridges 10 enlarge the outer diameter of the cable 1 for
applications
where larger diameters are desirable, such as for fixing the cables 1 in
napped
carrier sheets, or boards that are usually used for installing heating pipes
or
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heating conducts. Moreover, such ridges 10 enhance the gripping or clamping
effect of the cable 1 when arranged at napped cable carrier sheets or plates,
cable laying boards, concrete reinforcements and the like.
It should be clear that the embodiment described above only serves as an
example and is not to be understood to be restrictive. In fact, changes and
modifications are possible without straying from the scope of protection
defined
by the attached claims. Thus, all of the conductors 2 and 4 may also be
embedded in the matrix 3, to give just one example. In this case one may
dispense with the application of the covering layer 5.
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