GB2138638A - Cable Gland - Google Patents

Abstract

Glands for mineral insulated cables include a pot having a threaded bore by which the pot is secured to the cable. When urging the pot onto the cable the torque applied may twist the cable and cause the mineral powder surrounding the cable cores to drop out. The present invention provides a gland for mineral insulated cables comprising a pot (16) having a bore (20) with a discontinuous thread form (22). The pot is situated in a body (10) which is releasably secured to the cable e.g. by an end cap (28) and an "olive" 30. <IMAGE>

Description

SPECIFICATION Cable Gland This invention relates to a gland for mineral insulated cable.

The glands which are used at present for mineral insulated cables include a "pot" having the form of a cylinder which is open at one end, the closed end being provided with a threaded bore. In use the mineral insulated cable is urged through the threaded bore usually while twisting the pot relative to the cable. The effort required to fit the pot onto the cable may be considerable, particularly if the cable is slightly over-size.

Frequently the torque applied in order to fit the pot as aforesaid causes the cable to twist. In addition, when forcing the pot onto the cable, vibrations are imparted to the cable. As a result of the twisting and/or vibrations the mineral powder surrounding the cable cores may drop out of the cable so that there will be insufficient insulation between the cores and the cladding.

The present invention has been made with this problem in mind.

According to the invention there is provided a gland for mineral insulated, metal-clad, cables, said gland cqmprising a body, a pot receivable within the body, a bore in said pot, said bore being at least partially provided over at least a part of its surface with a discontinuous thread form whereby the pot can be substantially permanently secured to the cladding of the cable and means for releasabiy securing the body to the cable.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Fig. 1 is a longitudinal section of a gland fitted to mineral insulated cable; and Fig. 2 is a section on an enlarged scale of a part of the gland of Fig. 1.

Referring to the drawing the gland comprises a hollow body 10 externally threaded at one end 12 for engagement in the wall of a junction box or other electrical fitting. End 12 is of internally enlarged cross-section so as to define an internal shoulder 1 4. The end 1 2 of the body receives a pot 16.

The pot has the form of a hollow cylinder. One end 1 8 is closed and provided with a bore 20, the surface of which has a discontinuous thread 22 formed therein (Fig. 2). The other end of the pot has a wall of reduced thickness 24 so that it can be bent into the position shown in Fig. 1 The body 10 is externally threaded at its other end 26 for engagement by an end cap 28. The body and end cap between them engage an "olive" 30 on the cable 32 in a manner known per se by which the body is releasably secured to the cable.

In use the required amount of the cladding and insulation of the cable 32 is removed to expose the conductors 34. The bore 20 of the pot is then forced onto the cable cladding, this being possible to effect manually by virtue of the discontinuous thread formation in the bore. The pot may be then packed with compound 36 or a preformed body and a disc 38 placed at the open end of the pot, the disc being held in place by bonding over the end 24 of the pot into the position shown in Fig.

1.

As mentioned above, the discontinuous thread form in bore 20 enables the pot to be secured onto the cable quite easily. In other words less effort, particularly less torque, is required to fit the pot onto the cable. As a consequence there is less tendency for the cable to be twisted as the pot is fitted thereon and less tendency for vibrations to be transmitted to the cable. Thus there is less disturbance to the mineral powder insulation.

Although the pot is easier to fit onto the cable than prior art arrangements it nevertheless can be fixed to the cable at least as securely. Once fixed to the cable the pot may, in many cases, be more difficult to remove than in prior art assemblies.

The discontinuous thread may be as illustrated in Fig. 2, that is to say a normal thread divided by a plurality of spaced-apart unthreaded zones 23 which extend parallel to the axis of the pot. Other configurations can be used, however. For example the unthreaded zones can extend helically around the surface of bore 20. The size and number of such unthreaded zones are also not critical.

If desired a lubricant can be applied to the bore 20 to assist engagement on the cable. A preferred form of lubricant is one which will also form a fluid-tight seal between the pot and the cable.

1. A gland for mineral insulated metal-clad cables, said gland comprising a body, a pot receivable within said body, a bore in the pot, said bore being at least partially provided over at least a part of its surface with a discontinuous thread form whereby the pot can be substantially permanently secured to the cladding of the cable, and means for releasably securing the body to the cable.

2. A gland as claimed in Claim 1, wherein the thread form in the bore of the pot is a substantially normal thread form divided by a plurality of spaced apart unthreaded zones.

3. A gland as claimed in Claim 2, wherein the pot is cylindrical and unthreaded zones extend parallel to the axis of the pot.

4. A gland as claimed in Claim 2, wherein the unthreaded zones extend helically around the surface of the bore.

5. A gland as claimed in any preceding claim wherein a lubricant is provided on the surface of the bore.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cable Gland This invention relates to a gland for mineral insulated cable. The glands which are used at present for mineral insulated cables include a "pot" having the form of a cylinder which is open at one end, the closed end being provided with a threaded bore. In use the mineral insulated cable is urged through the threaded bore usually while twisting the pot relative to the cable. The effort required to fit the pot onto the cable may be considerable, particularly if the cable is slightly over-size. Frequently the torque applied in order to fit the pot as aforesaid causes the cable to twist. In addition, when forcing the pot onto the cable, vibrations are imparted to the cable. As a result of the twisting and/or vibrations the mineral powder surrounding the cable cores may drop out of the cable so that there will be insufficient insulation between the cores and the cladding. The present invention has been made with this problem in mind. According to the invention there is provided a gland for mineral insulated, metal-clad, cables, said gland cqmprising a body, a pot receivable within the body, a bore in said pot, said bore being at least partially provided over at least a part of its surface with a discontinuous thread form whereby the pot can be substantially permanently secured to the cladding of the cable and means for releasabiy securing the body to the cable. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Fig. 1 is a longitudinal section of a gland fitted to mineral insulated cable; and Fig. 2 is a section on an enlarged scale of a part of the gland of Fig. 1. Referring to the drawing the gland comprises a hollow body 10 externally threaded at one end 12 for engagement in the wall of a junction box or other electrical fitting. End 12 is of internally enlarged cross-section so as to define an internal shoulder 1 4. The end 1 2 of the body receives a pot 16. The pot has the form of a hollow cylinder. One end 1 8 is closed and provided with a bore 20, the surface of which has a discontinuous thread 22 formed therein (Fig. 2). The other end of the pot has a wall of reduced thickness 24 so that it can be bent into the position shown in Fig. 1 The body 10 is externally threaded at its other end 26 for engagement by an end cap 28. The body and end cap between them engage an "olive" 30 on the cable 32 in a manner known per se by which the body is releasably secured to the cable. In use the required amount of the cladding and insulation of the cable 32 is removed to expose the conductors 34. The bore 20 of the pot is then forced onto the cable cladding, this being possible to effect manually by virtue of the discontinuous thread formation in the bore. The pot may be then packed with compound 36 or a preformed body and a disc 38 placed at the open end of the pot, the disc being held in place by bonding over the end 24 of the pot into the position shown in Fig. 1. As mentioned above, the discontinuous thread form in bore 20 enables the pot to be secured onto the cable quite easily. In other words less effort, particularly less torque, is required to fit the pot onto the cable. As a consequence there is less tendency for the cable to be twisted as the pot is fitted thereon and less tendency for vibrations to be transmitted to the cable. Thus there is less disturbance to the mineral powder insulation. Although the pot is easier to fit onto the cable than prior art arrangements it nevertheless can be fixed to the cable at least as securely. Once fixed to the cable the pot may, in many cases, be more difficult to remove than in prior art assemblies. The discontinuous thread may be as illustrated in Fig. 2, that is to say a normal thread divided by a plurality of spaced-apart unthreaded zones 23 which extend parallel to the axis of the pot. Other configurations can be used, however. For example the unthreaded zones can extend helically around the surface of bore 20. The size and number of such unthreaded zones are also not critical. If desired a lubricant can be applied to the bore 20 to assist engagement on the cable. A preferred form of lubricant is one which will also form a fluid-tight seal between the pot and the cable. CLAIMS

1. A gland for mineral insulated metal-clad cables, said gland comprising a body, a pot receivable within said body, a bore in the pot, said bore being at least partially provided over at least a part of its surface with a discontinuous thread form whereby the pot can be substantially permanently secured to the cladding of the cable, and means for releasably securing the body to the cable.

2. A gland as claimed in Claim 1, wherein the thread form in the bore of the pot is a substantially normal thread form divided by a plurality of spaced apart unthreaded zones.

3. A gland as claimed in Claim 2, wherein the pot is cylindrical and unthreaded zones extend parallel to the axis of the pot.

4. A gland as claimed in Claim 2, wherein the unthreaded zones extend helically around the surface of the bore.

5. A gland as claimed in any preceding claim wherein a lubricant is provided on the surface of the bore.

6. A gland as claimed in Claim 5 wherein the lubricant is adapted to form a fluid-tight seal between the pot and the cable.

7. A gland for mineral insulated metal-clad cables substantially as described herein with reference to the accompanying drawings.