Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HEATING CABLE SUBSTANTIALLY FREE
FROM ELECTROMAGNETIC FfELD
FIELD OF THE INVENTIOf~I
The present invention relates to a heating cable designed for producing
substantially no electromagnetic field.
BACKGROUND OF THE INVENTION
It is known to distribute heating cables on the plywood surface of an
unfinished floor as a heating system for the corresponding room. Once the
heating cables have been laid out, a grout mixturE: is poured and uniformly
spread over the plywood surface to cover the heating cables. The resulting
floor surface can be finished by installing, for example, ceramic tiles,
engineered wood flooring, vinyl flooring, etc.
A problem encountered with heating cables is that they produce
electromagnetic field that some allege may eventually cause health problems.
Scientists at Health Canada are aware that some studies have suggested a
possible link between ELF (Extremely Low Frequency) field exposure and
certain types of childhood cancer.
One type of heating cables comprise a pair of parallel heating wire
elements through which electric current flows in ~~pposite directions. It has
been determined that placing two heating wire elements in parallel is not
sufficient to eliminate the problematic electromagnetic field.
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Consequently, there is a need for a heating cable free from
electromagnetic field.
SUMMARY OF THE INVENTION
Accordingly, the present invention relatEa to a heating cable
substantially free from electromagnetic field, comprising a pair or spirally
twisted heating wire elements, and a tubular sheath made of electrically
conductive material covering the pair of spirally twisted heating wire
elements.
When the spirally twisted heating wire elements are supplied with a current of
given amplitude flowing in opposite directions in the heating wire elements,
the
electromagnetic fields from the respective wire elements cancel each other to
provide a heating cable substantially free from electromagnetic field.
The present invention also relates to a method of fabricating a heating
cable substantially free from electromagnetic field, comprising spirally
twisting
a pair of heating wire elements together, and covering the pair of spirally
twisted heating wire elements with a tubular shE;ath made of electrically
conductive material. Again, when the spirally twisted heating wire elements
are
supplied with a current of given amplitude flowing in opposite directions in
the
heating wire elements, the electromagnetic fields from the respective wire
elements cancel each other to provide a heating cable substantially free from
electromagnetic field.
The foregoing and other objects, advantages and features of the
present invention will become more apparent upon reading of the following
non-restrictive description of illustrative embodiment, thereof, given by way
of
example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
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In the appended drawings:
Figure 1 is a cross-sectional view, taken along line 2-2 of Figure 2, of a
non-restrictive illustrative embodiment of the heating cable according to the
present invention, substantially free from electromagnetic field;
Figure 2 is a side elevational view of the non-restrictive illustrative
embodiment of heating cable as shown in Figure 1; and
Figure 3 is a side elevationa! view of a section of a pair of spirally twisted
heating wire elements of the heating cable of Figures 1 and 2, showing the lay
of
these spirally twisted heating wire elements.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
The non-restrictive illustrative embodiment of the heating cable
according to the present invention, substantially free from electromagnetic
field, will now be described in connection with the appended drawings.
As illustrated in Figures 1 and 2, the heating cable substantially free
from electromagnetic field is generally designated by the reference 10. This
heating cable 10 comprises:
- a pair of spirally twisted heating wire elements 11 and 12;
- a metal sheath 13 covering the pair of spirally tvvisted heating wire
elements 11 and 12; and
- an insulating jacket 14 covering the metal sheath 13.
Heating wire element 11
The heating wire element 11 comprises a rE;sistance wire 110 whose
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electrical resistance (resistance by unit of length of resistance wire) is
adjusted
to produce heat when supplied with an electric c;urrenta For example, the
electrical resistance of the resistance wire 110 can be adjusted, taking into
consideration the total length of the heating wire element 11 in a typical
installation, to release a given amount of heat when supplied with alternating
current from, for example, a 120-Volt 60-Hz voltage aource commonly found in
residential, industrial and commercial buildings.
For example, the electrical resistance of the resistance wire 110 can be
adjusted by adjusting the diameter thereof.
Although the wire 110 can be made of coppE~r, it is within the scope of
the present invention to use a wire 110 made of another electrically
conductive
material, for example made of an electrically conductive metal other than
copper, or an electrically conductive metal alloy including copper and/or any
other suitable metal(s).
Still referring to Figures 1 and 2, the wire 110 is individually insulated by
means of electrical insulation 111. Insulation 111 c;an be made of extruded
plastic material such as polyethylene or polypropylene capable of withstanding
and conducting the heat generated by and released from the wire 110.
Heating wire element 12
In the herein disclosed non-restrictive illustrative embodiment, the
heating wire element 12 is substantially similar to the heating wire element
11.
Therefore, the heating wire element 12 is formed of a resistance ~rire
120 individually insulated by means of electrical insulation 121. Insulation
121
can be made of extruded plastic material such as polyethylene or
polypropylene capable of withstanding and conducting the heat generated by
and released from the wire 120.
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The resistance wire 120 has an electrical resistance (resistance by unit
of length of resistance wire) adjusted to produce heat when supplied with an
electric current. For example, the electrical resistance of the resistance
wire
5 110 can be adjusted, taking into consideration the total length of the
heating
wire element 11 in a typical installation, to release a given amount of heat
when supplied with alternating current from, for example, a 120-Volt 60-Hz
voltage source commonly found in residential, industrial and commercial
buildings.
For example, the electrical resistance of the resistance wire 120 can be
adjusted by adjusting the diameter thereof.
Although the wire 120 can be made of copper, it is within the scope of
the present invention to use a wire 120 made of another electrically
conductive
material, for example made of an electrically conductive metal other than
copper, or an electrically conductive metal alloy including copper and/or any
other suitable metal(s).
As better shown in Figure 3, the heating wire elements 11 and 12 are
spirally twisted with a given lay 15. The lay 15 corresponds to the length
required by the heating wire elements i 1 and 12 to be spirally twisted by 1
turn.
It has been found that, by spirally twisting the heating wire elements 11
and 12, the electromagnetic field from the heating wire element 11 and the
electromagnetic field from the heating wire element 12 cancel each other, of
course when the current has the same given amplitude in the two heating wire
elements 11 and 12, and the current flowing through the heating wire element
11 flows in a direction opposite to the current flowing through the heating
wire
element i 2. A lay 15 having a length equal to or shorter than 2 inches, for
example 1 5/8 inch long, has proved to be efficient in canceling the
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electromagnetic field.
Metal sheath 13
The metal sheath 13 is formed of a plurality of small-diameter
electrically-conductive metal wires braided together ilo form a tubular
shielding
and/or an electrically-conductive metal tape spirally wound or longitudinally
applied to the pair of spirally twisted heating wire elements. A first
function of
the metal sheath 13 is to ground the heating cable 10 through a connection to
the ground. A second function of the metal sheath 13 is to mechanically resist
to impacts as strong as 100 Ibs, the metal sheath 13 being designed for that
purpose.
Again, although the braided metal wires or the metal tape can be made
of copper, it is within the scope of the present invention to use another
electrically conductive material, for example an electrically conductive metal
other than copper, or an electrically conductive metal allay including copper
and/or any other suitable metal(s).
4f course, the metal sheath 13 will comprise braided wires and/or tape
made of a material capable of withstanding and conclucting the heat generated
by and released from the wires 110 and 120.
It is within the scope of the present invention to use a tubular metal
sheath of any suitable type other than a braided metal sheath or tape.
Insulating jacket 14
The insulating jacket 14 covering the metal sheath 13 can be made of
extruded plastic or elastomeric material with or without subsequent cross-
finking such as polyethylene or polypropylene capable of withstanding and
conducting the heat generated by and released from the wires 110 and 120.
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The function of the insulating jacket 14 is 1io electrically insulate the
metal sheath 13 from any surrounding structures.
However, in certain embodiments, no insulating jacket 14 is required.
As a non-limitative example, a heating cable 10 comprising a sheath 13 made
of stainless steel will require no insulating jacket 14.
Although the present invention has been described hereinabove by way
of a non-restrictive illustrative embodiment thereof, this embodiment can be
modified at will, within the scope of the appended claims, without departing
from the spirit and scope of the present invention.
