CN216564482U - Fireproof connection box - Google Patents

Abstract

A non-metallic flameproof coupling box, comprising: an enclosure comprising a body and a lid, the lid being engageable with the body to form a substantially enclosed volume; at least one port to the volume; and at least one conductive insert engaged with the port to receive the cable gland to provide direct access of the cable gland to the volume.

Description

Fireproof connection box

Technical Field

The invention relates to an electrical junction box.

Background

Modern infrastructures are largely served via power supply cables. Industrial plants, shipyards, marine facilities, and mines, in particular, have a large number of cable networks.

It is often required that the power cables are connected to other cables that branch out and supply different parts of the facility.

Typically, the cable connection is made inside the enclosure in order to protect the connection from interference and environmental influences. Such enclosures also prevent unauthorized persons from accessing the live conductor, thereby preventing accidental electrocution.

Such enclosures are known in the industry as junction boxes or terminal boxes, hereinafter collectively referred to as "junction boxes".

In some installations, additional safety requirements must be met to ensure that the coupling box is made safe for use. For example, additional design features must be incorporated into the coupling box in order to make the installation safe in potentially explosive environments. Such a junction box is generally referred to as an Ex (explosion proof) junction box.

Potentially explosive environments can arise due to the presence of flammable gases in, for example, chemical plants, offshore oil rigs, and underground coal mines, which are prone to methane production. Similarly, air containing combustible particulates or dust (such as in flour mills and the like) can also constitute a potentially explosive environment.

A variety of different explosion protection concepts are being used, each of which may be evaluated via a formal, specified protocol as appropriate for use in a particular explosive environment. The parameters used to determine the most appropriate concept of protection include the specific gas or dust present in a particular environment, the range of gases or dust present, the expected ambient temperature, and the expected likelihood of mechanical shock and damage. Based on these parameters, the areas in the plant can be classified accordingly, and the appropriate junction box with its accompanying protection concept can be chosen.

Despite the protection concept, each Ex-certified junction box is classified as suitable for certain environments. For example, group I devices are suitable for use underground in mines, subject to "biogas". Group IIA devices, group IIB devices, and group IIC devices are suitable for surface mounting in certain specified gaseous atmospheres. Group III mechanisms are suitable for use in environments subject to flammable clouds of dust.

One of the earliest and most widely used protection concepts is "fire protection", also denoted by the reference "Ex d".

The International Electrotechnical Commission (IEC) has established a series of international specifications for equipment in explosive locations, namely the IEC 60079 series of specifications.

IEC 60079-0 is a common specification applicable to all equipment for explosive locations, and IEC 60079-1 provides additional requirements specific to fire protection equipment labeled "Ex d" equipment in the industry.

In most countries, IEC specifications or similar specifications are referred to in the regulations of the respective countries, and formal certification of equipment for such standards is mandatory for facilities in applicable explosive regions. Formal certification of the device is conducted via approved test laboratory reports and approved certification authorities.

The Ex d protection concept is adapted to the spark generating device to be accommodated inside the enclosure and is supposed to catch fire inside the enclosure. The concept employs design requirements and performance requirements that prevent internal combustion/explosion events from being able to ignite surrounding potentially explosive environments (e.g., environments containing flammable gases or flammable dust clouds).

IEC design requirements and testing requirements for Ex d enclosures are stringent, and in particular require materials that can withstand aging testing and thereafter various mechanical tests including impact testing. The enclosure must also be able to withstand the specified internal pressures without being damaged or excessively deformed. In addition, it must be proven through testing that the ignition of the internal flammable gas will not ignite the surrounding air.

Specifically, IEC 60079-0 and IEC 60079-1 require the following:

a) the envelope must be able to withstand four times the average pressure generated during an internal fire, which is about 30 bar (3000 kPa). This is known as overpressure;

b) the enclosure must extinguish the gases vented during an internal fire, thereby preventing the ignition of potentially explosive atmosphere surrounding the enclosure. This is accomplished via a "flame path" that includes very tightly controlled dimensions on the enclosure interface between the cover and the body. These dimensions include the width of the interface from the inside to the outside of the enclosure, the gap formed between the mating surfaces of the interface, and the surface finish of the joint;

c) before all mechanical tests, the enclosure, its seals, and all other non-metallic parts of the enclosure must withstand 840 hours of heat resistance to heat, cold, and humidity;

d) if the enclosure is to be used in an underground coal mine (group I), the enclosure must also be able to withstand two 20 joule impacts without damage. This was simulated by allowing a 1kg hemispherical impact head to fall from a height of 2 metres;

e) non-metallic materials used in group I (mining) applications need to withstand exposure to oil and grease at elevated temperatures; and

f) a threaded access into the enclosure is required to contain at least 5 full threads. These threaded joints must also comply with flame path clearance requirements similar to those mentioned in point (b) above.

For enclosures that comply with these stringent specifications, especially enclosures made of non-metallic materials, cables terminated in an Ex d enclosure tend to do so via an openable and separately but adjacently joined "Ex e" portion of the enclosure that, together with the Ex d section, forms a composite enclosure. As used herein, "Ex e" refers to an alternative protection method known as "enhanced safety" that provides for the Ex e enclosure not to contain the spark-emitting components. The Ex d portion of such an enclosure houses the spark-emitting element and is generally completely sealed and not openable or accessible.

Obviously, such a composite Ex e/Ex d enclosure does not allow for direct entry of cables into the Ex d portion of the enclosure.

As a result of stringent design and testing requirements, certified Ex d enclosures that may be opened and have direct cable entry points, especially those certified for group I (mining) facilities, are typically constructed very robustly with thick metal walls to achieve the necessary strength. Cast iron, cast brass, heavy gauge steel or stainless steel products are commonly used.

A common requirement for electrical continuity between the armour of various joined cables is another reason for the use of even metal as an encasement material, which is heavy and subject to corrosion.

Non-metallic polymer Ex e coupling boxes with direct cable entry are known in the art. Some enclosures also incorporate molded grounding bars to achieve continuity of grounding between the inlets. However, none are currently made from polymeric materials due to the very demanding test requirements for direct cable entry into Ex d junction boxes for harsh mining environments.

The metal Ex d direct entry cable coupling box known in the art suffers from several problems. One such problem is that such enclosures are susceptible to corrosion, and particularly corrosion of the flame path surfaces that pose a safety risk. The flame path surface is easily scratched by a screwdriver or the like carelessly. Such damage renders the Ex d nature of the enclosure ineffective and dangerous. These enclosures are also generally heavy and expensive to produce. Additionally, such enclosures typically have threaded inlets with precisely matching threads for receiving the cable gland in use. As such, there are no other threads or other sized sealing sleeves to mate.

Accordingly, there is a need for a certified fire coupling box (preferably certified for group I) that can accept direct entry of cables, is at least IEC compliant, corrosion resistant, relatively light, provides electrical conductivity between connected armored cables as required, is less expensive to manufacture than existing Ex d coupling boxes, is easily and quickly manufactured with different sizes and types of gland entry threads, and has a flame path that is not easily susceptible to corrosion and scratch damage. The present invention is directed, at least in part, to a coupling box that meets these requirements.

Disclosure of Invention

The present invention provides a non-metallic Ex d junction box, comprising: an enclosure comprising a body and a lid, the lid being engageable with the body to form a substantially enclosed volume; at least one port to the volume; and at least one conductive insert engaged with the port to receive the cable gland to provide direct access of the cable gland to the volume.

Preferably, a plurality of ports are provided at spaced apart locations on the body, each having a respective conductive insert engaged therewith. The conductive insert may be formed of brass. The number of ports and the location of the ports on the body may vary as desired.

Each port may be of any suitable shape and, for example, in cross-section, each port may be circular.

The conductive inserts may be placed in electrical communication with each other using a continuous element. The continuous elements may be welded to the conductive insert and may be welded together at a joint where the continuous elements intersect. The continuous element may be formed of any suitable conductive material. Preferably, the continuous element is in the form of a copper rod.

The body may include an additional external ground terminal in electrical communication with the continuous element to facilitate external grounding of the coupling box.

The conductive insert may be threaded and may be sized as desired.

A flame path may be formed between opposing surfaces of the body and the cover. The upper surface of the body and the corresponding lower surface of the cover may be machined to selected tolerances as required.

The body and the lid may comprise corresponding complementary fastening formations for securing the body to the lid. The cover may include a plurality of apertures and the body may include a plurality of receptacles aligned with the apertures. One or more suitable fasteners (such as screws) may then be engaged with the apertures and the sockets to secure the cover to the body. Preferably, the screw and the socket are formed of stainless steel.

The envelope of the coupling box may be formed of a glass fibre reinforced thermosetting plastics material. This is a low friction material and is less likely to be scratched during use, which ensures that the flame path formed between the upper surface of the body and the lower surface of the cover remains intact.

The body may have any suitable shape in cross-section, for example circular, hexagonal or octagonal. This is not limiting.

The body may include a plurality of mounting formations on a lower surface of the body to mount the body to a suitable surface. The mounting formations may be in the form of a plurality of apertures. The body may be secured to the surface using one or more suitable fasteners. Preferably, this is done using a mounting plate. The mounting plate may comprise a mounting body having a plurality of apertures formed therein which, in use, are placed in register with corresponding apertures on the lower surface of the body as required. Suitable fasteners may be used to secure the body to the plate in the desired orientation.

Drawings

The invention is further described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 is a perspective view of a coupling box according to a first embodiment of the present invention;

FIG. 2 is a view from one side of the coupling box of FIG. 1;

FIG. 3 is a cross-sectional view of the coupling box of FIG. 2;

FIG. 4 is a cross-sectional view of the coupling box taken on line X-X in FIG. 1;

FIG. 5 is a perspective view of a mounting plate to be used in conjunction with the junction box according to the present invention;

FIG. 6 is a perspective view of a coupling box according to a second embodiment of the present invention; and

fig. 7 is a perspective view of a coupling box according to a third embodiment of the present invention.

Detailed Description

Fig. 1, 2 and 3 illustrate a coupling box according to a first embodiment of the present invention. The coupling box 10 includes an enclosure 12, the enclosure 12 including a body 14 and a cover 16, the cover 16 being engageable with the body 14 to form a substantially enclosed volume 18 (see fig. 3). The envelope 12 is formed from a suitable glass fibre reinforced thermosetting plastics material and is circular in cross-section.

A plurality of ports 20A, 20B, 20C to the volume 18 are provided at spaced apart locations on the body 14. Engaged within each port 20A, 20B, 20C is a respective threaded conductive insert 22A, 22B, 22C for receiving, in use, a respective cable gland (not shown).

The conductive inserts 22A, 22B, 22C may be any suitable size or shape as desired.

The conductive inserts 22A, 22B, 22C are placed in electrical communication with each other using a continuous element 24 (see fig. 3) in the form of a copper rod. The rods 24 are welded to the conductive inserts and to each other at a coupling 26, where the rods 24 meet.

An upper surface 14A of the body 14 and an opposing lower surface 16A of the cover 16 are machined to selected tolerances to form the flame path 28. The tolerance depends on the particular environment in which the coupling box will be used.

The body 14 and the cover 16 include corresponding complementary fastening formations, respectively designated 30 and 32, for securing the cover 16 to the body 14. Threaded sockets 30A, 30B, 30C … … 30N are provided in the wall of the main body 14. Corresponding apertures 32A, 32B, 32C … … 32N are formed in the wall of the lid 16. The sockets 30A, 30B, 30C … … 30N and the apertures 32A, 32B, 32C … … 32N are placed in alignment with one another and suitable threaded fasteners 34A, 34B, 34C … … 34N engage the complementary formations 30, 32, thereby securing the cover 16 to the body 14. Preferably, the fasteners 34A, 34B, 34C … … 34N and the threaded sockets are formed of stainless steel.

An external ground terminal 36 (see fig. 4) may optionally be provided on the body 14 to facilitate external grounding.

At the lower surface 14B of the body 14, a mounting formation 38 is provided to allow the enclosure 12 to be secured to a work surface or the like. Preferably, a mounting plate 40 (see fig. 5) is provided to facilitate attachment of the enclosure 12 to a desired surface. The mounting plate 40 includes a mounting plate body 42, the mounting plate body 42 having a recessed portion 42A of complementary shape to the enclosure 12. Mounting formations 44A, 44B, 44C, 44D are provided on the mounting plate body 42 to secure the mounting plate body 42 to a suitable surface using suitable fasteners (not shown). In use, a plurality of mounting apertures 46 provided at spaced apart locations on the mounting plate body 42 are placed in alignment with the mounting formations 38 on the lower surface 14B of the body 14. Threaded fasteners are then used to secure the enclosure 12 to the mounting plate 40 in the desired orientation.

The shape of the enclosure 12, the number of ports 20, and the location of the ports 20 on the body 14 may vary. Fig. 6 illustrates a coupling box 10A according to a second embodiment of the invention, wherein the enclosure 12A is octagonal. Fig. 7 illustrates a coupling box 10B according to a third embodiment of the invention, wherein three adjacent ports 50A, 50B, 50C are provided in the enclosure 12B. Otherwise, the joint boxes 10A and 10B are the same as the joint box 10.

Claims (9)

1. A non-metallic Ex d gang box, comprising: an enclosure comprising a body and a cover, the cover being engageable with the body to form a substantially enclosed volume; at least one port to the volume; and at least one conductive insert engaged with the port to receive a cable gland to provide direct access of the cable gland to the volume.

2. The non-metallic Ex d junction box of claim 1, wherein a plurality of ports are provided at spaced apart locations on said body, each port having a respective conductive insert engaged therewith.

3. The non-metallic Ex d coupling cassette of claim 1 or 2, wherein each port is circular in cross-section.

4. The non-metallic Ex d junction box of any of claims 1-3, wherein the conductive inserts are placed in electrical communication with each other using a continuous element.

5. The non-metallic Ex d coupling box of claim 4, wherein the body comprises an external ground terminal in electrical communication with the continuous element to facilitate external grounding of the coupling box.

6. The non-metallic Ex d coupling box of any of claims 1-5, wherein a flame path is formed between opposing surfaces of the body and cover, and wherein an upper surface of the body and a corresponding lower surface of the cover are machined to a selected tolerance.

7. The non-metallic Ex d junction box of any of claims 1 to 6, wherein the enclosure of the junction box is formed of a fiberglass reinforced thermoset plastic material.

8. The non-metallic Ex d junction box of any of claims 1-7, wherein the body comprises a plurality of mounting formations on a lower surface of the body to mount the body to a suitable surface.

9. The non-metallic Ex d junction box of claim 8, wherein said body comprises a mounting plate having a mounting body with a plurality of apertures formed therein, said apertures being placed in alignment with corresponding apertures on the lower surface of the body in use.

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