GB2202419A - Interconnection of electric heating elements - Google Patents

Abstract

Self-regulating heating elements 8,10 are terminated by connectors 14,16 and conveniently interconnected, particularly in a T-configuration, by means of two or more electric power cables 12A,12B. The heating elements may be cables comprising a PTC heating element (66 Fig 9) disposed between bus bars (62,64). Cables 12A,12B may be lengths of a single cable with a further cable 20 spliced to an intermediate portion of the single cable. <IMAGE>

Description

Interconnection of Electric heating Elements This invention relates to the interconnection of elongate electric heating elements, particularly, though not exclusively self-regulating heating elements or tapes.

A single heating element may be terminated at one end by a plug that is engageable with a domestic or commercial socket of the electrical supply of a building, for example.

However, when two or more heating elements are to be supplied with power from a single point, are to extend from a point at a distance from a power socket, or are to be interconnected at a point remote from a socket, then a different connection arrangement has to be made.

In accordance with one aspect of the present invention there is provided an arrangement for interconnecting a plurality of elongate electric heating elements, comprising: at least two lengths of electric power cable; an electric connector attached to an end of each of said lengths; each connector being engageable with an associated connector that is attached to an end of a heating ele ment, thereby electrically to interconnect each of the heating elements.

The interconnection arrangement of the invention thus allows-heating elements, to be conveniently interconnected at any suitable location.

The arrangement is suited, for example, to providing an interconnection between three heating elements, and these may be arranged in a T-configuration. In this respect, the arrangement may comprise three of said lengths of power cable, wherein the other ends of each cable length are electrically interconnected, for example by means of at least one further connector.

Said cable lengths may comprise lengths of a single cable, wherein a portion of the insulation of the single cable is removed intermediate its ends, and wherein a third of said cable lengths is spliced to the single cable at the intermediate portion, which is subsequently reinsulated.

The heating elements may have a connector attached to each end thereof, and thus be of a predetermined length..

Such elements and interconnections are disclosed in our copending patent application number 8630336, the entire disclosure of which is incorporated herein by reference.

The connectors and associated connectors may be of any suitable configuration. When one end of each of two or more power cables are interconnected by a single connector, the connector of European Patent 0070696 may be employed.

Alternatively, the conductors of the power cables may be soldered or crimped together. Interconnection of the cables may be made using SOLDER SLEEVE connectors or DURASEAL connectors available from Raychem. Such connectors comprise a pre-insulated heat-shrinkable tube that can contain sealant material so that a splice can quickly and conveniently be made that is insulated, resistant to mechanical abuse, abrasion, and the ingress of water and other for example contaminating, fluids. As a further alternative, the interconnection between power cables, or between power cables and heating elements may employ an insulation piercing arrangement.

The electrical arrangement within a connector will depend on the particular configurations of the power cable and heating element. The power cable typically would have three conductors, for live, neutral and earth, and the heating element may have two bus bar conductors to be connected to live and neutral respectively, and may or may not have an outer, earthing braid. The heating cable may have additional conductors requiring other connections. Plug-in or screw-in connectors may be used, and if required these may be arranged so that for safety reasons they cannot be separated without their destruction, or without using E special tool.

If required, a further cable, a power supply cable, may be connected to the interconnection of the lengths of power cable of the arrangement. Thus for example, a T-splice arrangement may comprise three power cables interconnected at one or more points, which may be a connector in accordance with EP-B-0070696, and each power cable may have a heating element connected to opposite ends thereof. A further power cable, connected to an electricity supply, may be connected to that point or to one of the points. Alternatively, a power supply cable may be connected directly to a connector of a power cable length.

At least two of the lengths of power cable may comprise spaced-apart lengths of a single cable, and at least one other length of power cable may be spliced to (or branched off from) the single cable intermediate or beyond said spaced-apart lengths. Such splice (or branch) will involve the removal of a portion of the insulation of the single cable, and the insulation must be reinstated. the reinstatement may conveniently be effected by moulding around the splice (or branch).

Examples of self-regulating heater cables, which are the preferred form of heating elements of the arrangement, are disclosed in US Patents 3218384, 3296364, 3861029, 4072848, 4117312, 4185621, 4271350, 4309597, 4582983, 4574188, and in EP-A-0133748, the entire disclosures of which are included herein by this reference.

Also, in accordance with the present invention are arrangements that comprise heating elements, and arrangements that comprise heating elements that are connected to the lengths of power cables.

Although the invention finds particular application to the interconnection of three or more heating elements, it is also envisaged that the concept may also be applied to the interconnection of two heating elements. In such embodiment, a single power cable with a connector at each end may be engaged with associated connectors on the ends of the two heating elements. Alternatively, the two heating elements may be connected with respective ones of two power cable lengths that are themselves interconnected, and a further power cable may extend from that interconnection to a power supply.

Preferably, the heating elements of the arrangement of the invention comprise elongate self-regulating heating tapes as sold by Raychem under the trade names CHEMELEX and AUTOTRACE. Such tapes may comprise a positive temperature coefficient (PTC) heater material having two bus bar electrodes embedded therein, these components then being enclosed by a layer of electrically insulating material, and other layers, such as an earthing braid, as appropriate to the usage of the heating element. The tape is of generally flat configuration.

The present invention also provides a method of electrically interconnecting heating elements, in which one end of the elements are electrically connected to one or more lengths of power cable, advantageously using suitable power cable connectors or suitable power cable/heating element connectors.

It w-ill be appreciated that various combinations of power cable, connector, and heating element may be provided in accordance with the invention to give an arrangement suited to a particular application.

Embodiments of heating element connections in accordance with the present invention will now be described, by way of example, with reference to the accompanying schematic drawings.

Figure 1 shows a power supply cable 2 and a selfregulating heating element 4. The cable 2 and the heating element 4 are interconnected within a connector 6 which may be of two half-shell configuration or of female and male configuration.

Figure 2 shows two heating elements 8,10 and an intermediate power cable 12 that are connected in series by means of suitable connectors 14 and 16. Such a configuration constitutes an in-line splice.

Figure 3 shows a modification of the arrangement of Figure 2, in that the power cable 12 is replaced by two cable lengths 12A, 12B (which may be lengths of a single cable 12) that are interconnected in (or that extends through) a three-way, T-splice connector 18. The third arm of the T-splice is provided by a further power cable 20, that may be connected to a power supply for energising the heating elements 8 and 10. Such a configuration constitutes a powered in-line splice.

Figure 4 shows a modification of the arrangement of Figure 3, whereby instead of the third power cable 20 being connected to a power supply, it is terminated in a connector 22, which may be a one part or a two part connector, that also terminates a third self-regulating heating element 24.

Such a configuration constitutes a T-splice.

Figure 5 shows a modification of the arrangement of Figures 3 and 4, in providing a powered T-splice. The three heating elements 8,10,24 are connected by respective connectors 14,16,22 to respective power cables 12A, 12B, 20.

The power cables feed into a four way connector 26, the fourth arm of which is provided by a power supply cable 28 that is arranged to energise the heating elements 8,10,24.

Figure 6 shows a modification of Figures 4 and 5, in that instead, of the power cables extending from their interconnection in a T-configuration they can conveniently extend undirectionally therefrom. The three heating elements 8,10,24 extend parallel to one another, and the corresponding power cable lengths 12A,12B, 20 also extend parallel to one another into a connector 30. The connector 30 is shown partially cutaway, and it can be seen that the cable lengths 12A and 12B are portions of a single cable 12.

A portion of the insulation of the cable 12 is cut away (centre-stripped) within the connector 30 so as to expose its conductors. Also within the connector 30, the insulation is removed from the end of the cable length 20, and its conductors are connected, for example by soldering, to respective ones of the conductors of the cable 12. The cables 12A, 12B,12 and 20 are held in the relative positioning shown in the figure, by a mould which is then filled with curable insulating material such as epoxy resin so as to form the connector 30.

A further modification of the last-described embodiment is shown in broken outline in Figure 6, in which a further power cable 32 is spliced to the cable 12 within the connector 30, in a manner similar to the splicing of cable 20 to cable 12. The power cable 32 extends from the connector to a power supply, for energising the heating elements.

The arrangements of Figures 3,4 5 and 6 require the interconnection between two or more power cables, but heating elements may be interconnected in a different manner, using connections only between power cables and heating elements.

Figure 7 shows one such different arrangement for the interconnection of three heating elements 34,36,38. The elements 34 and 36 are connected by means of respective connectors 40,42 to one end of respective power cable lengths 44,46 in a similar manner to that shown in the preceding figures. The other ends of the cable lengths 44,46 are fed into connector 48 and therein are interconnected with each other and with the heating element 38. The power cable lengths 44 and 46 may be part of a single cable, the conductors of which are spliced to the conductors of the heating element 38 within the connector 48.

As shown in broken outline, the arrangement of Figure 7 may be modified by arranging for the connector 40 to encompass an electrical interconnection of the same form as that within connector 48, so that a power cable 50 extends therefrom. The cable 50 may be a power supply cable, or may extend to a further connector and heating element.

The connectors, such as connector 6 of Figure 1, which interconnect a power cable to a heating element may be of any suitable conventional form for connecting together electric cables, and may be single component, hinged for example, or a two part box and lid, or two interengaging half shells. Alternatively, one component of a two-part connector may screw into another part, or two parts may plug into one another, being of the male/female kind. Electrical interconnection of the conductors within the connector may employ screw fittings, crimps, soldering etc. It is also envisaged that an insulation-piercing arrangement may be employed, and one example of this is shown in Figures 8 and 9, Figure 9 being an enlarged cross-section on the line IX - IX of Figure 8.

Referring to Figures 8 and 9, an elongate heating element 60 has two stranded bus bar conductors 62,64 embedded in a PTC heating material 66 that is enclosed within polymeric insulating material 68, an earthing braid 70, and an outer protective jacket 72. A power cable 74 has an outer insulating jacket 76, and individually insulated live, neutral, and earth conductors 78,80,82 respectively.

The heating element 60 and power cable 74 are interconnected by a connector 84 having a two part interengaging outer insulating housing 86. Within the housing 86, the heater outer jacket 72 is cut back to expose the earthing braid 70 to which the earth conductor 82 of the power cable 74 is connected. Heater bus bars 62 and 64 are connected to the neutral and live conductors 80 and 78 respectively of the power cable 74 by respective connecting elements 88 and 90. Referring particularly to Figure 9, showing the connection of element 88 in more detail, the connecting element 88 comprises an annular metal cage 92 that receives therein the heating element stripped back to its insulation 68. An insulation piercing screw 94 is threaded through the cage 92 so as to cut through the insulation 68, pass through the PTC material 66, and engage the bus bar 62. Furthermore, insulation-piercing teeth 96 project inwardly from the cage 92 to engage the bus bar 62 in opposition to the screw 94 to ensure good electrical connection therebetween. The neutral power cable conductor 80 is connected to the metal cage 88, to complete interengagement with the heating element bus bar 62. Connecting element 90 likewise effects interengagement between the bus bar 64 and the live power cable conductor 78.

The housing 86 may be filled with insulating potting compound such as epoxy resin.

Claims (5)

1. An arrangement for interconnecting a plurality of elongate electric heating elements, comprising: at least two lengths of electric power cable; an electric connector attached to an end of each of said lengths; each connector being engageable with an associated connector that is attached to an end of a heating ele ment, thereby electrically to interconnect each of the heating elements.

2. An arrangement according to claim 1, comprising three of said lengths of power cable, wherein the other ends of each cable length are electrically interconnected by means of at least one further connector.

3. An arrangement according to claim 1 or 2, wherein two of said cable lengths comprise lengths of a single cable, wherein a portion of the insulation of the single cable is removed intermediate its ends, and wherein a third of said cable lengthsvis spliced to the single cable at the intermediate portion, which is reinsulated.

4. An arrangement according to any one of the preceding claims, comprising at least two of said heating elements, each of which has a said associated connector attached to one end thereof the associated connectors being interconnected to respective ones of said connectors.

5. A heater interconnection arrangement substantially as hereinbefore described with reference to the accompanying drawings.

5. A heater interconnection arrangement substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS 1. An arrangement for interconnecting a plurality of elongate electric heating elements, comprising: at least two lengths of electric power cable that are electrically interconnected with each other; an electric connector attached to an end of each of said lengths; each of said connectors being engageable with an associated connector that is attached to an end of a respective heating element, thereby electrically to interconnect each of the at least two heating elements.

2. An arrangement according to claim 1, comprising three of said lengths of power cable, wherein the other ends of each cable length are electrically interconnected by means of at least one further connector.

3. An arrangement according to claim 1 or 2, wherein two of said cable lengths comprise lengths of a single cable, wherein a portion of the insulation of the single cable is removed intermediate its ends, and wherein a third of said cable lengths is spliced to the single cable at the intermediate portion, which is reinsulated.

4. An arrangement according to any one of the preceding claims, comprising at least two of said heating elements, each of which has a said associated connector attached to one end thereof the associated connectors being interconnected to respective ones of said connectors.