CA1338315C - Cut to length heater cable - Google Patents
Cut to length heater cableInfo
- Publication number
- CA1338315C CA1338315C CA 612696 CA612696A CA1338315C CA 1338315 C CA1338315 C CA 1338315C CA 612696 CA612696 CA 612696 CA 612696 A CA612696 A CA 612696A CA 1338315 C CA1338315 C CA 1338315C
- Authority
- CA
- Canada
- Prior art keywords
- heater wire
- heating cable
- cable
- fibreglass
- electrode wires
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heater elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heater elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/40—Heating elements having the shape of rods or tubes
- H05B3/54—Heating elements having the shape of rods or tubes flexible
- H05B3/56—Heating cables
Abstract
An electrical heating cable includes at least two electrode bus wires arranged parallel to one another. The electrodes are electrically bridged at spaced apart locations by a heater wire having greater electrical resistance than said electrodes. The bus wire is fabricated from a metal having a high positive temperature coefficient (PTC) and high resistivity.
Description
-The present invention relates to the field of heating cable.
There exists in the market two general types of parallel type constructed heating cable that compete with one another for maximum usage in the residential, commercial and process industries. These cables incorporate heating elements that are electrically connected in parallel, either continuously or in zones, so that the watt density per lineal length is maintained, irrespective of any change in length of the heating cable. The parallel zone type of heating cable comprises two or more parallel insulated electrode wires around which a resistance wire is helically wrapped. The electrode wires are alternately bared at discrete points or zones along their length permitting current to flow through the resistance wire which becomes hot due to its high resistance. The cable is then covered with one or more insulating coatings. This form of cable has advantages: it is relatively inexpensive and easy to manufacture, and it will repeatedly reach a predetermined heat output at a known voltage applied across the electrode wires. It has some disadvantages though: it is susceptible to damage and it has limited usage in situations of variable ambient temperatures, such as those encountered in heating or maintenance of temperature sensitive products.
The second type of cable is known as a continuous self-limiting or self-regulating cable. It comprises of two or more parallel electrode wires which are embedded in an electrically conductive polymer matrix. The primary cable construction is then covered with one or more insulating coatings. Application of voltage across the electrodes will cause current to flow through the electrically resistive matrix and will develop heat. Typically this type of heater cable must be cross-linked to stabilize the operating characteristics of the finished product. At an elevated operating temperature, the current flow will diminish, due to increased resistance of the polymer matrix. It will be understood, then, that this form of cable finds favourable application in situations of variable ambient temperature, because it will regulate its thermal output when the combined effect of the ambient temperature and the heat developed by the cable creates a change of resistance in the matrix. As the conductive matrix is a compound, incremental thermal output will vary which results in hot and cold spotting along the length of the finished cable. This type of heater cable is also characterized with a high start-up inrush which demands the utilization of oversized distribution wiring and circuit breaker design.
The object of the present invention is to provide an inexpensive heating cable with the advantages possessed by each F~
of the foregoing heating cables and minimize or eliminate the relative disadvantages.
In a broad aspect, the present invention relates to a heating cable including at least a side by side pair of insulated electrode wires, short circuited along their lengths by heater wire wrapped helically around same and contacting alternate ones of same at spaced apart locations along their length at which the insulation on said wires has been removed;
a layer of fibreglass yarn wrapped around said heater wire wrapped electrode wires; and a coating of insulating material over said fibreglass yarn.
In drawings which illustrate the present invention by way of example:
Figure 1 is a perspective view, partially cut away, of an embodiment of the present invention having two or three electrode wires;
Figure 2 is a chart of the performance curve in watt/ft plotted against temperature (F) of the cable of the present invention; and Figure 3 is a schematic of a manufacturing process which may be utilized to make the cable of the present invention.
Referring first to Figure l, the cable of the present invention is provided with at least two electrode bus wires (1) ~ 1 33831 5 which are covered with a temperature rated and electrically insulating jacket (2). The electrode wires may be in a parallel side by side or spiralled configuration. The electrode insulation is stripped away at regular alternate intervals (3) to expose the bus wires. A resistance wire or element exhibiting PTC (positive temperature coefficient) is helically wound over the electrode bus wire construction (4).
It will be observed, then, that the resistance wire (4) will bridge the electrode from side to side where the insulation layers are removed. When the electrodes are connected to line voltage, current will flow in the resistance wire, causing it to increase in temperature and give the cable its heating capability.
The resistance wire (4) utilized by the present invention has PTC characteristics, and is made from an alloy exhibiting PTC properties, such as a 70 Ni, 30% Fe alloy, available as KANTHAL 7 oTM from The Kanthal Corporation of Connecticut; or BALCO ALLOY 400TM, available from Carpenter Technology of Toronto, Ontario.
The present invention also provides a fibreglass layer preferably helically wound, over the resistance wire. Fibre-glass yarn (5) may be wound onto the wire using apparatus utilized to wrap the resistance wire on a heater cable as shown schematically in Figure 3. It has been found that in this way ~ 1 33 83 1 5 a fibreglass layer can be applied three to five times faster to the cable construction than with conventional braiding techniques. Moreover, advantages are associated with the fibreglass layer. For instance, flexibility is imparted to the cable while protecting the resistance wire from breakage in the event of impact or repeated thermal cycling. To complete the cable construction, a further temperature rated layer (6) covers the fibreglass layer.
The present invention is further illustrated by way of tests carried out on the cable of the present invention, as follows:
Test Proce~ UL e:
A 10' (3m) section of double electrode VPC-501 (applicant's designation for cable produced in accordance with the present invention) is placed on the power output verification text fixture, which consists of a 2" (50mm) carbon steel pipe connected to a circulating system. The pipe is insulated with 1~" (36mm) fibreglass and covered with weather barrier. The circulating system is turned on and the pipe temperature is brought down to the desired temperature. The cable is energized at the rated voltage and allowed to reach equilibrium. The amperage is then recorded. This process is repeated at several specified temperatures. The data is charted to determine the cable's characteristic performance curve, the results being shown in Figure 2.
Test Results:
The pipe temperature was increased from 25F (14C) to 150F (66C). Amperage readings were taken and power outputs calculated. The test results are illustrated graphically in the form of a performance curve of power output (w/ft) versus pipe temperature (F) [see Figure 3].
Conclusion:
The cable's power output at equilibrium decreased by approximately 13.3% from 50F to 150F. From published literature on KANTHAL 70TM (available from Kanthal Corporation directly), a 25% change in resistance is expected over this temperature range. The discrepancy arises from the Kanthal literature being based on strand (heater element) temperature and not pipe temperature. Put another way, equilibrium power (strand resistance) is a function of actual strand temperature and not necessarily the pipe/ambient temperature.
A 25% change would occur only if the strand temperature varied from 50F (10C) to 150F (66C). In actuality the VPC
element is operating over a higher and narrower temperature range.
It should be noted, however, that due to the variations of sheath heat transfer coefficient increasing with increasing temperature and sheath to strand temperature differences decreasing with decreasing wattage, variances in strand temperatures between pipe temperatures of 10C and 66C are much less.
The temperature versus power results can be seen below, as well as in Figure 2.
VPC-501 Performance Curve Percent Change Temperature Wt/Ft W/N From 50F (10C) 50F (10C) 17.16 56.28 ---75F (24C) 15.96 52.36 -7.0%
100F (38C) 15.48 50.78 -9.8%
125F (152C) 15.36 50.39 -10.5%
150F (166C) 14.88 43.81 -13.3%
It is to be understood that the examples described above are not meant to limit the scope of the present invention. It is expected that numerous variants will be obvious to the person skilled in the design and manufacture of heating cable art, without any departure from the spirit of the present invention. The appended claims, properly construed, form the only limitation upon the scope of the present invention.
~. ''
There exists in the market two general types of parallel type constructed heating cable that compete with one another for maximum usage in the residential, commercial and process industries. These cables incorporate heating elements that are electrically connected in parallel, either continuously or in zones, so that the watt density per lineal length is maintained, irrespective of any change in length of the heating cable. The parallel zone type of heating cable comprises two or more parallel insulated electrode wires around which a resistance wire is helically wrapped. The electrode wires are alternately bared at discrete points or zones along their length permitting current to flow through the resistance wire which becomes hot due to its high resistance. The cable is then covered with one or more insulating coatings. This form of cable has advantages: it is relatively inexpensive and easy to manufacture, and it will repeatedly reach a predetermined heat output at a known voltage applied across the electrode wires. It has some disadvantages though: it is susceptible to damage and it has limited usage in situations of variable ambient temperatures, such as those encountered in heating or maintenance of temperature sensitive products.
The second type of cable is known as a continuous self-limiting or self-regulating cable. It comprises of two or more parallel electrode wires which are embedded in an electrically conductive polymer matrix. The primary cable construction is then covered with one or more insulating coatings. Application of voltage across the electrodes will cause current to flow through the electrically resistive matrix and will develop heat. Typically this type of heater cable must be cross-linked to stabilize the operating characteristics of the finished product. At an elevated operating temperature, the current flow will diminish, due to increased resistance of the polymer matrix. It will be understood, then, that this form of cable finds favourable application in situations of variable ambient temperature, because it will regulate its thermal output when the combined effect of the ambient temperature and the heat developed by the cable creates a change of resistance in the matrix. As the conductive matrix is a compound, incremental thermal output will vary which results in hot and cold spotting along the length of the finished cable. This type of heater cable is also characterized with a high start-up inrush which demands the utilization of oversized distribution wiring and circuit breaker design.
The object of the present invention is to provide an inexpensive heating cable with the advantages possessed by each F~
of the foregoing heating cables and minimize or eliminate the relative disadvantages.
In a broad aspect, the present invention relates to a heating cable including at least a side by side pair of insulated electrode wires, short circuited along their lengths by heater wire wrapped helically around same and contacting alternate ones of same at spaced apart locations along their length at which the insulation on said wires has been removed;
a layer of fibreglass yarn wrapped around said heater wire wrapped electrode wires; and a coating of insulating material over said fibreglass yarn.
In drawings which illustrate the present invention by way of example:
Figure 1 is a perspective view, partially cut away, of an embodiment of the present invention having two or three electrode wires;
Figure 2 is a chart of the performance curve in watt/ft plotted against temperature (F) of the cable of the present invention; and Figure 3 is a schematic of a manufacturing process which may be utilized to make the cable of the present invention.
Referring first to Figure l, the cable of the present invention is provided with at least two electrode bus wires (1) ~ 1 33831 5 which are covered with a temperature rated and electrically insulating jacket (2). The electrode wires may be in a parallel side by side or spiralled configuration. The electrode insulation is stripped away at regular alternate intervals (3) to expose the bus wires. A resistance wire or element exhibiting PTC (positive temperature coefficient) is helically wound over the electrode bus wire construction (4).
It will be observed, then, that the resistance wire (4) will bridge the electrode from side to side where the insulation layers are removed. When the electrodes are connected to line voltage, current will flow in the resistance wire, causing it to increase in temperature and give the cable its heating capability.
The resistance wire (4) utilized by the present invention has PTC characteristics, and is made from an alloy exhibiting PTC properties, such as a 70 Ni, 30% Fe alloy, available as KANTHAL 7 oTM from The Kanthal Corporation of Connecticut; or BALCO ALLOY 400TM, available from Carpenter Technology of Toronto, Ontario.
The present invention also provides a fibreglass layer preferably helically wound, over the resistance wire. Fibre-glass yarn (5) may be wound onto the wire using apparatus utilized to wrap the resistance wire on a heater cable as shown schematically in Figure 3. It has been found that in this way ~ 1 33 83 1 5 a fibreglass layer can be applied three to five times faster to the cable construction than with conventional braiding techniques. Moreover, advantages are associated with the fibreglass layer. For instance, flexibility is imparted to the cable while protecting the resistance wire from breakage in the event of impact or repeated thermal cycling. To complete the cable construction, a further temperature rated layer (6) covers the fibreglass layer.
The present invention is further illustrated by way of tests carried out on the cable of the present invention, as follows:
Test Proce~ UL e:
A 10' (3m) section of double electrode VPC-501 (applicant's designation for cable produced in accordance with the present invention) is placed on the power output verification text fixture, which consists of a 2" (50mm) carbon steel pipe connected to a circulating system. The pipe is insulated with 1~" (36mm) fibreglass and covered with weather barrier. The circulating system is turned on and the pipe temperature is brought down to the desired temperature. The cable is energized at the rated voltage and allowed to reach equilibrium. The amperage is then recorded. This process is repeated at several specified temperatures. The data is charted to determine the cable's characteristic performance curve, the results being shown in Figure 2.
Test Results:
The pipe temperature was increased from 25F (14C) to 150F (66C). Amperage readings were taken and power outputs calculated. The test results are illustrated graphically in the form of a performance curve of power output (w/ft) versus pipe temperature (F) [see Figure 3].
Conclusion:
The cable's power output at equilibrium decreased by approximately 13.3% from 50F to 150F. From published literature on KANTHAL 70TM (available from Kanthal Corporation directly), a 25% change in resistance is expected over this temperature range. The discrepancy arises from the Kanthal literature being based on strand (heater element) temperature and not pipe temperature. Put another way, equilibrium power (strand resistance) is a function of actual strand temperature and not necessarily the pipe/ambient temperature.
A 25% change would occur only if the strand temperature varied from 50F (10C) to 150F (66C). In actuality the VPC
element is operating over a higher and narrower temperature range.
It should be noted, however, that due to the variations of sheath heat transfer coefficient increasing with increasing temperature and sheath to strand temperature differences decreasing with decreasing wattage, variances in strand temperatures between pipe temperatures of 10C and 66C are much less.
The temperature versus power results can be seen below, as well as in Figure 2.
VPC-501 Performance Curve Percent Change Temperature Wt/Ft W/N From 50F (10C) 50F (10C) 17.16 56.28 ---75F (24C) 15.96 52.36 -7.0%
100F (38C) 15.48 50.78 -9.8%
125F (152C) 15.36 50.39 -10.5%
150F (166C) 14.88 43.81 -13.3%
It is to be understood that the examples described above are not meant to limit the scope of the present invention. It is expected that numerous variants will be obvious to the person skilled in the design and manufacture of heating cable art, without any departure from the spirit of the present invention. The appended claims, properly construed, form the only limitation upon the scope of the present invention.
~. ''
Claims (5)
1. A heating cable including at least a side by side pair of insulated electrode wires, short circuited along their lengths by heater wire wrapped helically around same and contacting alternate ones of same at spaced apart locations along their length at which the insulation on said wires has been removed;
a layer of fibreglass yarn wrapped around said heater wire wrapped electrode wires; and a coating of insulating material over said fibreglass yarn.
a layer of fibreglass yarn wrapped around said heater wire wrapped electrode wires; and a coating of insulating material over said fibreglass yarn.
2. A heating cable as described in Claim 1, wherein said fibreglass yarn is wound helically around said heater wire wrapped electrode wires.
3. A heating cable as described in Claim 2, wherein said heater wire is a nickel iron alloy wire exhibiting high resistivity.
4. A heating cable as described in Claim 3, wherein said heater wire is a nickel iron alloy wire exhibiting a high positive temperature coefficient (PTC behaviour).
5. A heating cable as described in any one of claims 1 to 4, wherein said fibreglass yarn is sufficiently thick to serve to cushion said heater wire from breakage upon impact, and from breakdown due to thermal cycling.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 612696 CA1338315C (en) | 1989-09-22 | 1989-09-22 | Cut to length heater cable |
| GB9006851A GB2236236A (en) | 1989-09-22 | 1990-03-27 | Electric heating cable |
| DE19904030183 DE4030183A1 (en) | 1989-09-22 | 1990-09-24 | ELECTRIC HEATING CABLE |
| FR9011762A FR2652477A1 (en) | 1989-09-22 | 1990-09-24 | CUT TO LENGH HEATER CABLE. |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 612696 CA1338315C (en) | 1989-09-22 | 1989-09-22 | Cut to length heater cable |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1338315C true CA1338315C (en) | 1996-05-07 |
Family
ID=4140662
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 612696 Expired - Lifetime CA1338315C (en) | 1989-09-22 | 1989-09-22 | Cut to length heater cable |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1338315C (en) |
| DE (1) | DE4030183A1 (en) |
| FR (1) | FR2652477A1 (en) |
| GB (1) | GB2236236A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04272680A (en) * | 1990-09-20 | 1992-09-29 | Thermon Mfg Co | Switch-controlled-zone type heating cable and assembling method thereof |
| GB2390004A (en) * | 2002-03-08 | 2003-12-24 | Martin Cook | Flexible heating element |
| ES1058126Y (en) * | 2004-07-20 | 2005-02-16 | Termoelectrica Vila S A | AIR CONDITIONING DEVICE FOR VEHICLES AND SIMILAR |
| ES2327463T3 (en) * | 2006-03-03 | 2009-10-29 | Nv Bekaert Sa | CABLES OF GLASS METAL FILAMENTS COVERED FOR USE IN HEATING TEXTILES WITH ELECTRICAL ENERGY. |
| CN106851878A (en) * | 2016-12-15 | 2017-06-13 | 安邦电气股份有限公司 | A kind of automatic temperature-control electric heating belt |
| CN109068424A (en) * | 2018-08-06 | 2018-12-21 | 芜湖市旭辉电工新材料有限责任公司 | A kind of alloy wire heating cable processing method |
| RU205291U1 (en) * | 2020-06-03 | 2021-07-07 | Алексей Александрович Малтабар | HEATING CABLE |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3757086A (en) * | 1972-10-05 | 1973-09-04 | W Indoe | Electrical heating cable |
| US4037083A (en) * | 1976-05-05 | 1977-07-19 | Leavines Joseph E | High temperature parallel resistance pipe heater |
| US4459473A (en) * | 1982-05-21 | 1984-07-10 | Raychem Corporation | Self-regulating heaters |
| CH662231A5 (en) * | 1982-09-13 | 1987-09-15 | Eilentropp Hew Kabel | FLEXIBLE ELECTRIC RENDERABLE HEATING OR TEMPERATURE MEASURING ELEMENT. |
| DE3243061A1 (en) * | 1982-11-22 | 1984-05-24 | HEW-Kabel Heinz Eilentropp KG, 5272 Wipperfürth | Flexible, electrical extendable heating element |
| DE3233904A1 (en) * | 1982-09-13 | 1984-03-15 | HEW-Kabel Heinz Eilentropp KG, 5272 Wipperfürth | Flexible electrical heating or temperature measurement strip |
| US4604516A (en) * | 1983-07-19 | 1986-08-05 | Athena Controls Inc. | Cascaded arrangement for electrically heating fluids to high temperature |
| US4700054A (en) * | 1983-11-17 | 1987-10-13 | Raychem Corporation | Electrical devices comprising fabrics |
| DE3636738A1 (en) * | 1986-10-29 | 1988-05-05 | Eilentropp Hew Kabel | REMOVABLE FLEXIBLE ELECTRIC HEATING ELEMENT |
| US4922083A (en) * | 1988-04-22 | 1990-05-01 | Thermon Manufacturing Company | Flexible, elongated positive temperature coefficient heating assembly and method |
-
1989
- 1989-09-22 CA CA 612696 patent/CA1338315C/en not_active Expired - Lifetime
-
1990
- 1990-03-27 GB GB9006851A patent/GB2236236A/en not_active Withdrawn
- 1990-09-24 FR FR9011762A patent/FR2652477A1/en not_active Withdrawn
- 1990-09-24 DE DE19904030183 patent/DE4030183A1/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| GB9006851D0 (en) | 1990-05-23 |
| FR2652477A1 (en) | 1991-03-29 |
| GB2236236A (en) | 1991-03-27 |
| DE4030183A1 (en) | 1991-04-04 |
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