AU2021105156A4 - Flameproof junction box - Google Patents

Abstract

A non-metallic flameproof junction box which includes an enclosure comprising a body and a lid 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 for receiving a cable gland to provide direct entry of the cable gland to the volume. 16 10 12 22B 20A 20B 22A FIGURE 1 4 10 16 16A 14 28 20A4 20C 20B FIGURE 2

Description

10

12 22B

20A 20B

22A FIGURE 1 4

10

16 16A

14 28

A4 20C

20B FIGURE 2

FLAMEPROOF JUNCTION BOX BACKGROUND OF THE INVENTION

[0001] This invention relates to an electrical junction box.

[0001] Modern infrastructure is extensively serviced via electrical power supply

cables. Industrial plants, shipyards, marine installations, and mines in particular

have extensive cable networks.

[0002] Electrical power cables are frequently required to connect to other cables

which branch out and supply different parts of an installation.

[0003] Typically the cable connections are made inside an enclosure in order to

protect the connections from interference and from the environment. Such

enclosures also preclude unauthorised persons from accessing the live

conductors thereby preventing accidental electrocution.

[0004] Such enclosures are referred to in the trade as junction boxes or terminal

boxes, hereinafter collectively referred to as "junction boxes".

[0005] In certain installations, additional safety requirements must be met, to

ensure that the junction boxes are rendered safe for use. For example, additional

design features must be incorporated into a junction box in order to render the

installation safe in a potentially explosive environment. Such junction boxes are

generally referred to as Ex (Explosion Protected) junction boxes.

[0006] Potentially explosive environments can arise due to the presence of

combustible gas in, for example, chemical plants, offshore oil rigs and underground methane-prone coal mines. Similarly, atmospheres containing combustible particulates or dust such as in flour-milling plants and the like may also constitute potentially explosive environments.

[0007] Various different explosion protection concepts are in use, each of which

can be assessed via formal specified protocols as being suitable for use in specific

hazardous environments. Parameters which are used in order to determine the

most appropriate protection concept include the specific gas or dust which is

present, the extent of gas or dust present, the expected ambient temperature and

the probability of mechanical impact and damage anticipated in the particular

environment. Predicated upon these parameters, an area in a plant can be

classified accordingly and an appropriate junction box with its attendant protection

concept can be chosen.

[0008] Notwithstanding the protection concept, each Ex certified junction box is

classified as being suitable for certain environments. For example, Group I

equipment is suitable for use underground in mines, subject to "firedamp". Group

IIA, IIB and IIC devices are suitable for surface installations in certain specified

gas atmospheres. A Group III apparatus is suitable for use in environments

subject to flammable dust clouds.

[0009] One of the oldest and most extensively used protection concepts is

"flame-proofing," also referred to by the designation, "Ex d".

[0010] The International Electrotechnical Commission (IEC) has produced a

series of international specifications for equipment in hazardous locations, namely

the IEC 60079 series of specifications.

[0011] IEC 60079-0 is a general specification applicable to all equipment for

hazardous locations and IEC 60079-1 provides extra requirements, specific to

flameproof equipment which in the industry is designated "Ex d" equipment.

[0012] In most countries, the IEC specifications or similar specifications are

referred to in the respective country's legislation, and formal certification of

equipment to such standards is mandatory for installations in the applicable

hazardous areas. The formal certification of the equipment is done via accredited

test laboratory reports and accredited certification authorities.

[0013] The Ex d protection concept caters for spark producing equipment to be

housed inside an enclosure and assumes that there could be an ignition inside the

enclosure. The concept employs design and performance requirements that

prevent an internal combustion/explosion event from being able to ignite a

surrounding potentially explosive environment e.g. one which contains flammable

gas or a flammable dust cloud.

[0014] The IEC design and testing requirements for Ex d enclosures are rigorous

and require, inter alia, materials that can withstand an ageing test and thereafter

withstand various mechanical tests, including an impact test. The enclosure must

also be capable of withstanding a specified internal pressure without sustaining

damage or undue deformation. Additionally, it must be demonstrated, via testing,

that an internal ignition of a combustible gas will not ignite the surrounding

atmosphere.

[0015] Specifically, IEC 60079-0 and IEC60079-1 require the following: a) the enclosure must be able to withstand four times the average pressure developed during an internal ignition, which is approximately 30 bar (3000 kPa). This is known as overpressure; b) the enclosure must quench the gasses expelled during an internal ignition, so as to prevent the ignition of a potentially explosive atmosphere around the enclosure. This is achieved via a "flame path" which comprises very tightly controlled dimensions on the enclosure interface, between the lid and body. These dimensions include the width of the interface from the inside of the enclosure to the outside face, the gap formed between the mating faces of the interface, and the surface finish of the joint; c) the enclosure, its seal and all other non-metallic parts of the enclosure, must withstand 840 hours of thermal endurance to heat, cold and humidity, prior to all mechanical tests; d) if the enclosure is to be used in underground coal mines (Group I), then it must also be able to withstand two 20 Joule impacts without damage. This is simulated by allowing a 1kg hemispherical impact head to fall from a height of 2 meters; e) non-metallic materials used in Group I (mining) applications, need to withstand exposure to oils and grease at elevated temperature; and f) threaded entries into enclosures are required embody at least 5 full threads. These threaded joints must also be subject to the flame path gap requirements similar to those mentioned in point (b) above.

[0016] For an enclosure to comply with these rigorous specifications, especially

an enclosure which is made of non-metallic material, cables terminating in an Ex d

enclosure often do so via an openable and separate but adjacently joined "Ex e"

portion of the enclosure which, together with the Ex d section, forms a compound

enclosure. "Ex e", as used herein, refers to an alternative protection method

known as "Increased Safety" which dictates that an Ex e enclosure must not

house sparking components. The Ex d portion of such an enclosure houses the

sparking elements and is generally completely sealed and not openable or

accessible.

[0017] Clearly, such compound Ex e/Ex d enclosures do not allow direct entry of

the cables into the Ex d portion of the enclosure.

[0018] As a result of the stringent design and test requirements, certified Ex d

enclosures which are openable and which have direct cable entry points,

especially those certified for Group I (mining) installations, are typically very

robustly constructed with thick metal walls to achieve the requisite strength. The

use of cast iron, cast brass, heavy steel or stainless steel fabrications is common.

[0019] A frequent requirement for electrical continuity between the armouring of

various joined cables is another reason for metal being used as the enclosure

material, even though the material is heavy and is subject to corrosion.

[0020] Non-metallic polymeric Ex e junction boxes with direct cable entries are

known in the art. Some enclosures also incorporate moulded earthing rods to

achieve earthing continuity between entries. However, because of the very harsh test requirements for direct cable entry Ex d junction boxes for hostile mining environments, currently none are made of a polymeric material.

[0021] Metallic Ex d direct entry cable junction boxes known in the art suffer

several problems. One such problem is that such enclosures are susceptible to

corrosion and, in particular, corrosion of the flame-path faces which poses a safety

risk. The flame-path faces are easy to inadvertently scratch with a screwdriver or

the like. Such damage negates the Ex d properties of the enclosure and is

dangerous. These enclosures are also generally heavy and expensive to produce.

Additionally, such enclosures usually have a threaded entry for receiving a cable

gland in use, with an exact matching thread. As such, no other thread or size

gland will fit.

[0022] There is therefore a need for a certified flameproof junction box (preferably

certified for Group I installations) which can accept direct entry of cables, is at

least IEC compliant, is corrosion resistant, is comparatively light, provides

electrical conductivity between connected armoured cables if required, is less

expensive to manufacture than existing Ex d junction boxes, is easy to

manufacture quickly with different sizes and types of gland entry threads and has

a flame-path which is not readily susceptible to corrosion and scratch damage.

The invention aims, at least partially, to provide a junction box which meets these

requirements.

SUMMARY OF INVENTION

[0023] The invention provides a non-metallic Ex d junction box which includes an

enclosure comprising a body and a lid 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 for receiving a cable gland to provide direct entry of the cable gland to the volume.

[0024] Preferably a plurality of ports are provided at spaced apart locations on

the body, each having a respective conductive insert engaged therewith. The

conductive inserts may be formed from brass. The number of ports and the

location thereof on the body may be varied according to requirement.

[0025] Each port may be of any appropriate shape and, for example, in cross

section, each port may be circular.

[0026] The conductive inserts may be placed in electrical communication with

each other using continuity elements. The continuity elements may be soldered to

the conductive inserts and may be soldered together at a junction at which the

continuity elements intersect. The continuity elements may be formed from any

suitable conductive material. Preferably, the continuity elements are in the form of

copper rods.

[0027] The body may include an additional external earth terminal in electrical

communication with the continuity elements to facilitate external earthing of the

junction box.

[0028] The conductive inserts may be threaded and may be sized according to

requirement.

[0029] A flame-path may be formed between opposing surfaces of the body and

lid. An upper surface of the body and a corresponding lower surface of the lid may

be machined to a selected tolerance, according to requirement.

[0030] The body and the lid may include corresponding complementary fastening

formations for securing the body to the lid. The lid may include a plurality of

apertures and the body may include a plurality of sockets which are in register with

the apertures. One or more suitable fasteners, such as screws, may then be

engaged with the aperture and the socket in order to secure the lid to body.

Preferably the screws and sockets are formed from stainless steel.

[0031] The enclosure of the junction box may be formed from a glass fibre

reinforced thermoset plastic 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 a lower surface of the lid, remains

intact.

[0032] The body may have any suitable shape in cross-section e.g. circular,

hexagonal or octagonal. This is not limiting.

[0033] The body may include a plurality of mounting formations on a lower

surface thereof, for mounting 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, use in

made of a mounting plate. The mounting plate may include a mounting body with

a number of apertures formed therein, which in use, are placed in register with

corresponding apertures on the lower surface of the body, according to

requirement. Suitable fasteners may be used to secure the body to the plate in the

desired orientation.

DESCRIPTION OF THE DRAWINGS

[0034] The invention is further described by way of examples with reference to

the accompanying drawings in which:

Figure 1 is a perspective view of a junction box according to a first embodiment of

the invention;

Figure 2 is a view from one side of the junction box in Figure 1;

Figure 3 is cross-sectional view of the junction box in Figure 2;

Figure 4 is cross-sectional view of the junction box taken on a line X-X in Figure 1;

Figure 5 is perspective view of a mounting plate to be used in conjunction with a

junction box according to the invention;

Figure 6 is a perspective view of a junction box according to a second

embodiment of the invention; and

Figure 7 is a perspective view of a junction box according to a third embodiment of

the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] Figures 1, 2 and 3 illustrate a junction box according to a first embodiment

of the invention. The junction box 10 includes an enclosure 12 comprising a body

14 and a lid 16, engageable with the body 14, to form a substantially enclosed

volume 18 (see Figure 3). The enclosure 12 is formed from a suitable glass-fibre

reinforced thermoset plastic material and is circular in cross-section.

[0036] 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 a respective

cable gland (not shown), in use.

[0037] The conductive inserts 22A, 22B, 22C may be of any suitable size or

shape according to requirement.

[0038] The conductive inserts 22A, 22B, 22C are placed in electrical

communication with each other using continuity elements 24 (see Figure 3) in the

form of copper rods. The rods 24 are soldered to the conductive inserts and to

each other at a junction 26 at which the rods 24 intersect.

[0039] The upper surface 14A of the body 14 and the opposing lower surface

16A of the lid 16 are machined to a selected tolerance to form a flame-path 28.

The tolerance is dependent on the particular environment in which the junction box

is to be used.

[0040] The body 14 and the lid 16 include corresponding complementary

fastening formations designated 30 and 32 respectively, for securing the lid 16 to

the body 14. Threaded sockets 30A, 30B, 30C...30N are provided in a wall of the

body 14. Corresponding apertures 32A, 32B, 32C...32N are formed in a wall of

the lid 16. The sockets 30A, 30B, 30C...30N and the apertures 32A, 32B,

32C...32N are placed in register with each other and suitable threaded fasteners

34A, 34B, 34C... 34N are engaged with the complementary formations 30, 32

thereby to secure the lid 16 to the body 14. Preferably the fasteners 34A, 34B,

34C...34N and the threaded sockets are formed from stainless steel.

[0041] An external earth terminal 36 (see Figure 4) may optionally be provided on

the body 14 to facilitate external earthing.

[0042] At a lower surface 14B of the body 14, mounting formations 38 are

provided to allow the enclosure 12 to be secured to a work surface or the like.

Preferably, a mounting plate 40 (see Figure 5) is provided to facilitate the

attachment of the enclosure 12 to a desired surface. The mounting plate 40

includes a mounting plate body 42 having a recessed portion 42A of

complementary shape to the enclosure 12. Fixing 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 a suitable fastener (not shown). A number of mounting

apertures 46, provided at spaced apart locations on the mounting plate body 42

are, in use, placed in register with the mounting formations 38 on the lower

surface 14B of the body 14. A threaded fastener is then used to secure the

enclosure 12 to the mounting plate 40 in a desired orientation.

[0043] The shape of the enclosure 12, the number of ports 20 and the locations

of the ports 20 on the body 14 may vary. Figure 6 illustrates a junction box 10A

according to a second embodiment of the invention wherein the enclosure 12A is

octagonal. Figure 7 illustrates a junction box 10B according to a third embodiment

of the invention wherein three adjacent ports 50A, 50B, 50C are provided on the

enclosure 12B. In other respects, the junction boxes 10A and 1OB are the same as

the junction box 10.

[0044] The reference to any prior art in this specification is not, and should not be

taken as, an acknowledgement or any form of suggestion that such prior art forms

part of the common general knowledge.

[0045] It will be understood that the terms "comprise" and "include" and any of

their derivatives (e.g. comprises, comprising, includes, including) as used in this

specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0046] In some cases, a single embodiment may, for succinctness and/or to

assist in understanding the scope of the disclosure, combine multiple features. It is

to be understood that in such a case, these multiple features may be provided

separately (in separate embodiments), or in any other suitable combination.

Alternatively, where separate features are described in separate embodiments,

these separate features may be combined into a single embodiment unless

otherwise stated or implied. This also applies to the claims which can be

recombined in any combination. That is a claim may be amended to include a

feature defined in any other claim. Further a phrase referring to "at least one of" a

list of items refers to any combination of those items, including single members.

As an example, "at least one of: a, b, or c" is intended to cover: a, b, c, a-b, a-c, b

c, and a-b-c.

[0047] It will be appreciated by those skilled in the art that the disclosure is not

restricted in its use to the particular application or applications described. Neither

is the present disclosure restricted in its preferred embodiment with regard to the

particular elements and/or features described or depicted herein. It will be

appreciated that the disclosure is not limited to the embodiment or embodiments

disclosed, but is capable of numerous rearrangements, modifications and

substitutions without departing from the scope as set forth and defined by the

following claims.

Claims (5)

1. A non-metallic Ex d junction box which includes an enclosure comprising a

body and a lid 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 for receiving a cable gland to provide direct entry of

the cable gland to the volume.

2. A non-metallic Ex d junction box according to claim 1 wherein a plurality of

ports are provided at spaced apart locations on the body, each port having a

respective conductive insert engaged therewith.

3. A non-metallic Ex d junction box according to claim 2 wherein the conductive

inserts are placed in electrical communication with each other using

continuity elements.

4. A non-metallic Ex d junction box according to any one of claims 1 to 3

wherein a flame-path is formed between opposing surfaces of the body and

lid, and wherein an upper surface of the body and a corresponding lower

surface of the lid are machined to a selected tolerance.

5. A non-metallic Ex d junction box according to any one of claims 1 to 4

wherein the enclosure of the junction box is formed from a glass fibre

reinforced thermoset plastic material.