Link disconnect box for an electrical distribution network protector

A link disconnect box enables easy field retrofitting of network protectors. The link disconnect box has an outer casing that defines a cavity with a front face opening and top and bottom bus bar openings. Top and bottom terminals seal the top and bottom bus bar openings. The bottom terminal is configured to connect to an existing terminal of the network protector. A removable face plate seals shut the front face opening. Top and bottom bus bars electrically connect to the top and bottom terminals, extending through the respective top and bottom bus bar openings towards each other, with an air gap between them within the cavity. An electrical link, which can be bolted closed, connects and disconnects the top and bottom bus bars by electrically bridging the air gap.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to electrical power distribution systems. In particular, the present invention relates to a link disconnect box that allows for the easy isolation of a network protector switch from load side connections.

2. Description of the Related Art

The distribution of electricity in urban centers involves medium voltage (up to 35 kV) electrical cables (called “feeders”) connecting a power substation to the utility customer base. In the vicinity of the customer, connections are made from the feeder to a transformer that reduces the voltage to one capable of being utilized by the customer. In order to sectionalize the feeder, that is, to isolate the feeder in the event of an electrical fault, three phase power breakers called network protectors are installed on the low voltage side of the transformer. The customer connection side (“load side”) of various network protectors can be shorted together to create a low voltage electrical grid (“network”), which provides reliable power service to the utility customer. Secondary power lines extend from the low voltage electrical grid to the consumers, and as a result a failure of any single transformer in the grid does not disrupt power to the consumers.

There are presently tens of thousands of these network protectors in operation in urban electrical centers throughout the world. Each network protector operates as an automatic switch, connecting or disconnecting the related transformer to the network based upon the monitoring of electrical conditions. A network protector comprises a large three phase switch/breaker element installed in an enclosure, which can be a submersible tank or a non-submersible cabinet. The switch element is connected on one side to the low voltage side of a transformer and on the other side to the network. Because the load side of the network protector can be connected to the load side of other network protectors in a network system, there is an enormous amount of electrical energy available at any one network protector. Protecting utility workers from this energy while they are servicing network protectors is of paramount importance.

As indicated above, the network protector acts as a three-phase switch between the low-voltage side of a transformer and the customer. When a transformer, network protector or both need to be serviced, the feeder to the transformer can be isolated so as to prevent high voltage current from reaching the transformer using an electrical switch between the feeder and the transformer. However, because of the networked connections on the low voltage side of the network protector, it is not possible to isolate the network protector itself from low voltage current. Consequently, the customer side of the network protector remains energized, and this can present serious safety issues for linemen, particularly in the form of arc flash when servicing the network protector.

It is therefore desirable to provide a link disconnect box that can be retrofitted onto the existing terminals of a network protector so that, once installed, linemen can readily disconnect a network protector from a low voltage network.

SUMMARY OF THE INVENTION

In one aspect, a link disconnect box for a voltage distribution network is disclosed. The link disconnect box has an outer casing that define a cavity, a front face opening, a top bus bar opening, and a bottom bus bar opening. A top terminal is disposed over the top bus bar opening, while a bottom terminal is disposed over the bottom bus bar opening. The bottom terminal is configured to electrically and mechanically connect to an existing terminal of a network protector in the voltage distribution network. A face plate removably covers the front face opening. A top bus bar electrically couples to the top terminal and extends through the top bus bar opening, and a bottom bus bar electrically couples to the bottom terminal and extends through the bottom bus bar opening. An air gap electrically isolates the top bus bar from the bottom bus bar within the cavity. An electrical link connects and disconnects the top bus bar and the bottom bus bar by electrically bridging the air gap.

In a preferred embodiment, the face plate sealingly covers the front face opening, the top terminal sealingly covers the top bus bar opening, and the bottom terminal sealingly covers the bottom bus bar opening. In such embodiments, the face plate may further include an air pressurization port for pressurizing the cavity.

In one embodiment the bottom terminal comprises through holes configured to align with connectors, such as bolts or threaded holes, in the existing terminal of the network protector. In preferred embodiments, however, the bottom terminal has threaded openings that do not pass through the bottom terminal.

In various embodiments the bottom terminal comprises a bottom terminal plate covering the bottom bus bar opening and mechanically coupled to the bottom bus bar, and a terminal adapter plate removably connected to the bottom terminal plate. The terminal adapter plate has a first surface configured to mechanically and electrically engage with the bottom plate terminal, and a second surface configured to mechanically and electrically engage with the existing terminal of the network protector. Preferably, the bottom terminal plate has a larger surface area than the existing terminal of the network protector. In such embodiments the terminal adapter plate may have first through holes for coupling the terminal adapter plate to the bottom terminal plate, and second through holes for coupling the terminal adapter plate to the existing terminal of the network protector, in which the first through holes delimit a greater surface area than a surface area delimited by the second through holes. It may also be preferable that the bottom terminal plate has threaded openings that do not pass through the bottom terminal plate, with the first through holes aligning with the threaded openings.

In various embodiments the electrical link is configured to be mechanically secured in a closed position in which the air gap is bridged, and is further configured to fall under gravity into an open position in which the air gap is not bridged when not mechanically secured in the closed position. For example, the electrical link may include a swing arm for bridging the air gap, the swing arm having at least an opening, with the upper bus bar having a hole corresponding to the opening in the swing arm. A bolt can then be run through the opening in the swing arm and engage with the threaded hole in the upper bus bar to mechanically secure the link in the closed position.

In some embodiments the top terminal may have a mechanical configuration corresponding to the existing terminal of the network protector, so that secondary power lines can be readily moved from the existing terminal of the network protector to the top terminal. In other embodiments the top terminal is a spade terminal. In yet other embodiments the bottom terminal is a spade terminal.

In another aspect, a method for the field retrofitting of a network protector in a voltage distribution network is disclosed. Secondary power lines from an existing output terminal of the network protector are removed. A link disconnect box is electrically and mechanically coupled to the existing terminal of the network protector, with the secondary power lines electrically and mechanically coupled to the link disconnect box. The link disconnect box may have the structure described above, with the bottom terminal of the link disconnect box connecting to the existing terminal of the network protector, and the top terminal of the link disconnect box being used to connect to secondary power lines.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the invention provide a link disconnect box that can be field installed, for example, on top of the existing terminals of a network protector and that allows for the easy isolation of the network protector from the load side connections. Various embodiments of a link disconnect box may include a submersible box with one or more bolted links. When unbolted, the links fall and thereby isolate each phase of the network protector. The links may be unbolted using an extended insulated wrench to add distance between the worker and the electrical energy. The link disconnect box can be configured for mounting, for example, on existing spade or stud type terminals that are commonly used with network protectors. The link disconnect box may also be wall mounted. The link disconnect box can advantageously be mounted on network protectors already operating in the field, thus allowing a utility to gain a measure of protection for its workers without replacing equipment. Terminal adapters may be used to conform the terminals of the link disconnect box with the existing terminals of the network protector and with the secondary power lines that form the low voltage network.

Reference is initially drawn toFIGS. 1-5, which illustrate a first embodiment link disconnect box100that may be field-installed on a conventional network protector, and in particular on existing electric terminals of a network protector. Link disconnect box100includes an outer casing110that defines an internal cavity140, which is preferably a monolithic, molded structure made from any suitably durable and electrically insulating material, such as polyester glass, or epoxy, and having a front face opening112, a bottom bus bar opening114and a top bus bar opening116. A face plate120is used to cover the front face opening112, with a gasket122, such as made from rubber, interposed between the face plate120and the rim of front face opening112to ensure that the front face plate120makes a liquid-tight seal with the outer casing110. The face plate120may be made from the same material as that used for the outer casing110, or from any other suitable, electrically insulating material. Bolts121are used to secure front face plate120to the outer casing110, the bolts121engaging with corresponding threaded openings111set in the rim of front face opening112. Brass inserts or the like may be used to provide the corresponding threading within the openings111. To reduce the chances of ingress of liquids into cavity140, preferably the only openings in outer casing110are front face opening112, bottom bus bar opening114and top bus bar opening116.

The rim of front face opening112may be substantially square having, for example, a height113and a width115of 9 inches. Of course, other dimensions for the width115and height113are possible, but dimensions are preferred that provide sufficient access room for a lineman while remaining sufficiently small to ensure adequate spacing of the boxes100when mounted on a network protector. Hence, preferred embodiment widths115may be from 7 to 10 inches, and heights113may be from 7 to 12 inches.

A top surface117of the outer casing110is formed so as to provide a recess131for a top terminal130. Recess131, which may be substantially circular, surrounds top bus bar opening116. Top terminal plate132, which may be made from copper, optionally plated with silver or tin, is disposed within recess131. Preferably, universal top terminal plate132forms a liquid-tight seal with outer casing110. In certain preferred embodiments, the outer casing110is molded around universal top terminal plate132to ensure such a liquid-tight seal. Top terminal plate132is preferably shaped to be compatible with existing infrastructure, and in particular with standard connections used for the low voltage grid of an electrical power distribution system, such as spade terminals or the like. In a preferred embodiment, top terminal plate132has eight threaded holes134equidistantly aligned along a circle133having a diameter136of 3 and ¾ inches. Holes134preferably do not pass all the way through top terminal plate132. Threaded holes134are preferably sized to engage with ½ inch bolts. Recess131itself may therefore have a diameter139of, for example, 4 and ⅝ inches, with top terminal plate132then sized to fit snugly within, or be molded within, recess131. Top terminal plate132may have a thickness of about 1 inch.

A back surface141of the cavity140defined by outer casing110is shaped to have a top recess142aligned with top bus bar opening116, and within which is disposed a top bus bar150that extends through top bus bar opening116to physically and electrically contact top terminal plate132. Top bus bar150preferably makes a liquid-tight seal with top bus bar opening116. Although the term “bus bar” is used, it should be understood that here and in the following such electrical components are not limited to bar-like shapes, and that other shapes are possible, including tubes, rods or any other suitable shape. Hence, it should be understood that the term “bus bar” includes any suitable shape that is capable of carrying the currents intended for the link disconnect box. Top bus bar150may be, for example, brazed to the top terminal plate132. Top terminal plate132may include a recess137within which top bus bar150may be disposed to provide greater contact surface area between the electrical bus components132,150. Top bus bar150may be made from silver-plated copper, for example, and have a thickness of ⅝ of an inch to 2 inches, preferably about 1 inch, and a width of 3 to 4 inches. The depth of top recess142may be such that the top bus bar150lies flush with the back surface141when disposed within the recess142. Top bus bar150also preferably includes one or more threaded holes152, which are discussed below.

In a similar vein, a bottom surface119of outer casing110is formed so as to provide a recess161for a bottom terminal160. Recess161, which may be substantially rectangular but with semi-circular ends, surrounds bottom bus bar opening114. Note that both recess131on top surface117and recess161on bottom surface119may be set within respective protrusions138,168, such as circular or elliptical protrusions, extending from top surface117and bottom surface119, respectively, of outer casing110, as indicated in the figures for this specific embodiment. These protrusions138,168may give the outer casing110a total height102of, for example, about 12 inches. This is not, however, a requirement of the invention. However, such protrusions138,168do provide the benefit of providing a standoff distance from the surface of the network protector upon which link disconnect box100is mounted, which may make for easier installation of link disconnect box100onto the existing terminals of a network protector.

Bottom terminal plate162, which may be made from silver-plated copper, is disposed within recess161of protrusion168of outer casing110. Preferably, bottom terminal plate162is sealed within the recess161so as to provide a liquid-tight seal between bottom terminal plate162and outer casing110. By way of example, an adhesion promoter may be used so that the polyester glass bonds to the copper when molded. Bottom terminal plate162may be shaped to be compatible with existing infrastructure, and in particular with standard connections used for network protectors or shaped to properly mate with a specific make and/or model of network protector. In a preferred embodiment, bottom terminal plate162has six threaded holes164, three of which are equidistantly spaced along a first semi-circular end163of the bottom terminal plate162, and three of which are equidistantly spaced along an opposing second semi-circular end166of bottom terminal plate162. The threaded holes164are preferably sized to engage with ½ inch bolts. Protrusion168within which recess161is set may be elliptical, having a major axis169of, for example, 9 and ¾ inches, and a minor axis167of 9 inches. Bottom terminal plate162may have a thickness of about 1 inch, and a length165of about 8 and ¾ inches.

The back surface141of cavity140is further shaped to have a bottom recess146aligned with bottom bus bar opening114, and within which is disposed a bottom bus bar170that extends through bottom bus bar opening114to physically and electrically contact bottom terminal plate162. Bottom terminal plate162may include a recess167within which bottom bus bar170may be disposed to provide greater contact surface area between the components162,170. Bottom bus bar170may be made from silver-plated copper, for example, and have a thickness of from ⅝ of an inch to 2 inches, preferably 1 inch, and a width of 3 to 4 inches, similar to that of top bus bar150. The depth of bottom recess146may be such that bottom bus bar170lies flush with the back surface141when disposed within the recess146.

Top bus bar150extends down from top terminal plate132, through top bus bar opening116and to a top edge of a central recess144in back surface141. Similarly, bottom bus bar170extends up from bottom terminal plate162, through bottom bus bar opening114and to the bottom edge of central recess144. Central recess144is located within a central region of back surface141, and has a depth and width that preferably exceeds those of top recess142and bottom recess146. Central recess144provides a suitable air gap between top bus bar150and bottom bus bar170to electrically isolate top bus bar150from bottom bus bar170.

In one embodiment, top terminal plate132is first braised to top bus bar150, bottom terminal plate162is braised to bottom bus bar170, and then these components are set into a suitable mold so that molding material forming outer casing110is molded around top terminal plate132, top bus bar150, bottom terminal plate162and bottom bus bar170, thereby ensuring that these components are held firmly into position in a liquid- and air-tight manner.

An electrical link180is used to selectively electrically connect and disconnect top bus bar150and bottom bus bar170by electrically bridging air gap144existing between bus bars150and170. When electrically disconnecting top bus bar150from bottom bus bar170, link180with central recess144together ensure that an adequate air gap exists between these components150and170. Link180includes a base182that is firmly affixed, such as bolted, to bottom bus bar170, back surface141or both, and which is made from, for example, brass. A swing arm184is pivotally connected to base182, which may also be made from, for example, brass. Swing arm184is pivoted so as to swing up and down along the vertical direction as defined by bus bars150and170, with a pivot point185of swing arm184being at the lower end of swing arm184. When swung into the up, closed, position, swing arm184is substantially parallel to bus bars150and170; when swung into the down, open, position, swing arm184is substantially perpendicular to bus bars150,170and points towards front face opening112. A bus bar bridge186is fixedly connected, such as bolted, to the surface of swing arm184that faces bus bars150and170and at a position that is above pivot point185. Bus bar bridge186may be made, for example, from silver-plated copper and have a thickness from ⅝ of an inch to 1 inch, and preferably of about 1 inch. When link180is in the closed position, upper and lower ends of bus bar bridge186respectively contact upper bus bar150and lower bus bar170to electrically connect bus bars150and170together. Also, when in the closed position, one or more openings187in swing arm184align with one or more threaded holes152in upper bus bar150, so that one or more respective bolts188may run through openings187to threadedly engage with threaded holes152so as to bolt link180into the closed position. Nuts189may be disposed on each bolt188between swing arm184and top bus bar150to prevent bolts188from falling out of openings187when link180is in the open position. An electrical pathway provided by bottom terminal plate162, bottom bus bar170, bus bar bridge186, top bus bar150and top terminal plate132is designed to safely support the maximum electrical power load needed from the respective phase output port of the network protector. For example, the electrical pathway may be constructed so as to support current ranges from 800 Amperes to 5100 Amperes.

In use, face plate120may be unbolted from outer casing110so that a lineman can gain access to link180. Then, using an extended insulated wrench, the lineman can unscrew the one or more bolts188so that they disengage from threaded holes152. Swing arm184then swings down, opening link180and thus de-energizing one phase of the network protector from the low voltage network. Further, as pivot point185of swing arm184is positioned to be well below the center of mass of swing arm184, swing arm184will naturally tend to swing down into the open position and remain there, ensuring a naturally open position of link180to ensure the safety of the lineman. Once servicing of the network protector, transformer or both has been completed, link180may be once more bolted into the closed position by way of bolt(s)188and face plate120put back into place, thereby sealing shut cavity140.

In some embodiments, face plate120may include an air pressurization port124, of any suitable known design, that can be releasably connected to a pressurized air source to pressurize cavity140so as to further prevent ingress of any liquids into cavity140. Air pressurization port124may be any suitable one-way valve or the like, as known in the art, such as a ball valve, needle valve or the like, and may optionally be threaded.

FIG. 6illustrates a network protector1employing alternate embodiment link disconnect boxes200. Each link disconnect box200is substantially similar to link disconnect box100discussed above, but does not include the air pressurization port124and has a slightly modified bottom terminal plate262for bottom terminal260. Three link disconnect boxes200are installed on the top surface3of network protector1, one for each of the three phases output by network protector1on respective output terminals5. That is, network protector1has three existing output terminals5respectively for the three-phase power provided over the low voltage network. The protrusion268and related bottom terminal260of each link disconnect box200is installed onto a respective existing output terminal5of network protector1. As shown inFIG. 6, when the face plate220is removed, a lineman can gain access to the link280within each link disconnect box200to electrically connect and disconnect the respective terminal5of network protector1from the low voltage network.

FIGS. 7 and 8provide detailed views of connecting the link disconnect box200to a respective existing terminal5of the network protector1. A benefit of the design of various embodiment link disconnect boxes is that they can be readily retrofitted onto the existing terminals of any network protector1in the field, without any need to change or replace the existing terminal5of network protector1. Output terminal5of network protector1typically includes a top terminal plate7that has threaded holes9on an upper surface thereof and is used for the connection of secondary power lines for the low voltage network. The exact configuration of top terminal plate7may vary from manufacturer to manufacturer of network protectors1. Bottom protrusion268of link disconnect box200is shaped to accept existing top terminal plate7of network protector1. More specifically, the recess261, within which is disposed the bottom terminal plate262of link disconnect box200, is shaped to accept and engage with existing terminal5of network protector1. As shown inFIGS. 7 and 8, upper terminal plate7of network protector1fits snugly, and is entirely disposed within, recess261of link disconnect box200to abut against bottom terminal plate262. Holes264in bottom terminal plate262are designed to align with threaded holes9of top terminal plate7, and the terminal plates7and262rest snugly in direct physical contact with each other, as shown inFIG. 8. A rubber O-ring or gasket11may be disposed between the rim of recess261as provided by bottom protrusion268and the housing13of the terminal5so as to ensure a liquid-tight seal between link disconnect box200and network protector1. Bolts15are then disposed through each of the holes264in bottom terminal plate262to engage with threaded holes9in top terminal plate7of network protector1, thereby firmly mechanically and electrically coupling the terminal plates262and7together, and thus mechanically and electrically coupling link disconnect box200to network protector1.

FIGS. 9 and 10present perspective views of link disconnect box200installed on network protector1while in the closed position and open position, respectively. While in the normal operating condition so that network protector1is energized and connected to the low voltage network, front face plate220is bolted and sealed against gasket222to ensure cavity240remains sealed against the ingress of both air and liquids. Link280is bolted in the closed position, so that bus bar bridge286electrically connects top bus bar250with bottom bus bar270, and thus top terminal plate232with bottom terminal plate262. A spade terminal20may be bolted to top terminal plate232to provide for the electrical connection of secondary power lines of the low voltage network. Hence, top terminal plate232, as discussed above, is preferably formed as to mechanically correspond to spade terminal20, and in some embodiments may have the same mechanical configuration as output terminal5of network protector1—i.e., of top terminal plate7.

To de-energize network protector1from the low voltage network, face plate220is removed to expose and gain access to cavity240. An extended insulated wrench is used to unbolt link280from top bus bar250, and link280subsequently falls into the open position, thus creating an air gap between bus bars250and270and thereby de-energizing network protector1from the low voltage network. A lineman may thereafter safely work on network protector1without concern of energy from the low voltage network. Further, because each link disconnect box200de-energizes its respective phase terminal5, the lineman also does not need to worry about phase-to-phase arcing within network protector1, thereby further ensuring the safety of the lineman when servicing network protector1. Similar advantages are obtained by use of first embodiment link disconnect box100, as well.

A potential drawback of the embodiment link disconnect box200is that securing bolts15require access to cavity240, which may be inconvenient, particularly when working around bus bars250and270. Also, through holes264through which bolts15pass to mechanically engage with network protector1may permit the unwanted ingress of air, liquids or both into cavity240, despite the presence of O-ring11.

Embodiment300depicted inFIGS. 11 and 12avoids these drawbacks by having a bottom terminal plate362that has no through holes, unlike bottom terminal plate262in the embodiment link disconnect box200discussed above. Also, embodiment link disconnect box300makes use of a terminal adapter plate390that permits link disconnect box300to be field installed onto the existing terminal of any network protector, regardless of make or model. It will be appreciated that suitable terminal adapter plates390may also be made for the embodiment link disconnect boxes100,200or any other embodiment link disconnect box.

Link disconnect box300is substantially the same as first embodiment link disconnect box100and includes a lower protrusion368on the outer casing310that defines a recess361within which is disposed the bottom terminal plate362. Bottom terminal plate362may include a recess, protrusion or the like around its outer periphery, as shown inFIGS. 11 and 12, to better ensure rigid coupling with the walls of recess361. Bottom terminal plate362forms an air and liquid tight seal with lower protrusion368and includes a plurality of threaded holes364disposed in a predetermined pattern across the exterior surface of bottom terminal plate362, for example in a pattern as discussed previously with respect to first embodiment link disconnect box100. These threaded holes364do not pass all the way through bottom terminal plate362but extend upwards only partially into bottom terminal plate362. Preferably, link disconnect box300is designed so that bottom terminal plate362spans a larger surface area than an output terminal5of a target network protector1, or of most or even all known network protectors, and in particular is preferably designed so that threaded holes364delimit a greater surface area than that spanned by top terminal plate7of network protector1.

Adapter plate390is designed to fit within recess361and engage with bottom terminal plate362. Adapter plate390may be made from, for example, silver-plated copper and have a thickness of from ⅝ of an inch to 2 inches, preferably about 1 inch. Adapter plate390includes a first side391that is configured to abut immediately against bottom terminal plate362, and includes through holes394(or other suitable connector type) that align with threaded holes364(or other suitable corresponding connector type) of bottom terminal plate362. Bolts17(typically in conjunction with corresponding washers) may be passed through through holes394to threadedly engage with threaded holes364so as to securely mechanically and electrically connect adapter plate390to bottom terminal plate362. Adapter plate390has a second side392that is configured to abut immediately against top terminal plate7of output terminal5of network protector1, and includes through holes399that align with connectors on top terminal plate7that are on terminal5of network protector1. Such connectors are typically threaded holes9, although they may also include, by way of example, all-thread, bolts or the like. Hence, the shape of the first side391of adapter plate390preferably corresponds to the shape of bottom terminal plate362of link disconnect box300, and has a pattern of through holes394that correspond with the pattern of threaded holes364in the bottom terminal plate362. Similarly, the shape of the second side392of adapter plate390preferably corresponds to the shape of top terminal plate7of network protector1, and has a pattern of through holes399that correspond with threaded holes9in the top terminal plate7of network protector1. In preferred embodiments, the through holes399for the second surface392are configured so that bolts15may be completely disposed within the through holes399to extend from second side392. As such, through holes399preferably include a larger-diameter portion398that descends from first side391, and a smaller-diameter portion397that extends up from second side392; larger-diameter portions398are slightly larger and deeper than the diameter and height, respectively, of the heads of bolts15, while small-diameter portions397are smaller that the heads of bolts15but accept the shafts of bolts15. Bolts15(typically in conjunction with corresponding washers) may be passed through holes399to threadedly engage with threaded holes9in top plate terminal7of network protector1so as to securely mechanically and electrically connect adapter plate390to top terminal plate7.

To field install link disconnect box300onto an existing terminal5of network protector1, a lineman selects the proper terminal adapter plate390that corresponds to output terminal5of network protector1. The lineman removes the secondary power lines from existing output terminal5, and then installs the appropriate adapter plate390onto this existing output terminal5by placing the second surface392against the top plate terminal7, aligning the holes9and399with each other, and then passing bolts15(preferably with respective washers) through holes399to engage with threaded holes9of output terminal5. There is no need to exchange the existing output terminal5of network protector1for a new or different output terminal. Bolts15are selected so that their heads rest entirely within larger-diameter holes398and thus do not protrude above second surface392, and firmly mechanically and electrically connect adapter plate390to existing top terminal9. Link disconnect box300is then lowered onto adapter plate390so that bottom terminal plate362aligns with top surface391of adapter plate390. Because through holes394of adapter plate390extend outside output terminal5of network protector1, bolts17(preferably in conjunction with washers) may be easily passed through through holes394to engage with threaded holes364in bottom plate terminal362. Output terminal5of network protector1is thereby firmly mechanically and electrically connected to bottom plate terminal362of link disconnect box300via terminal adapter plate390. Secondary power lines from the low voltage network may then be coupled to the top terminal plate332by, for example, coupling a spade terminal to top terminal plate332using threaded holes334, and then coupling the secondary power lines to the spade terminal.

It will be appreciated that various types of terminal adapter plates390may be manufactured, each corresponding to a different make, model or both of network protector so that all makes and models of network protectors can be supported and used with any embodiment link disconnect box. Further, use of terminal adapter plates provides for more flexibility in the design of bottom terminal plates in the link disconnect boxes, so that a proprietary pattern or design may be used for the bottom terminal plates of the link disconnect boxes, yet these link disconnect boxes can still be easily and readily retrofitted and field installed onto the existing terminals of network protectors.

Not all network protectors include a relatively flat, horizontal surface for the output terminal. Some, for example, may have a spade-type terminal for an existing output terminal. In such situations, it may be desirable to employ a spade-to-spade connection to electrically connect an embodiment link disconnect box to such a network protector. An embodiment link disconnect box400is depicted inFIG. 13for such a connection, and includes a bottom spade terminal22and a top spade terminal20. Top spade terminal20may be used for connection to the secondary power lines of the low voltage network, while bottom spade terminal22may be used to mechanically and electrically connect to the existing spade terminal on the output port of a network protector. A suitably designed adapter plate may be used, for example, to connect bottom spade terminal22to the bottom plate terminal of link disconnect box400. Alternatively, the bottom plate terminal of link disconnect box400may be shaped in the form of a spade terminal or a standard spade terminal may be bolted to the bottom terminal plate.

FIG. 14is a cross-sectional view, illustrating the link disconnect box400being installed onto an existing output spade terminal5of network protector1. An adapter plate490can be used, which is bolted to the bottom terminal plate462of link disconnect box400. The adapter plate490has a first surface491shaped to mate with bottom terminal plate462of link disconnect box400, and a second surface492shaped to mate with a bottom face of spade terminal22, which may have a conventional shape. The top face of spade terminal22is used to electrically and mechanically connect to the output spade terminal5of network protector1, in which the faces of the spade terminals22,5are bolted to each other, thereby mechanically and electrically connecting link disconnect box400to network protector1.

For some network protectors, the existing terminal5and its related surrounding insulation are flush with respect to each other and the surrounding areas of the network protector, as shown inFIG. 15. To permit a lineman sufficient access to existing terminal5while connecting a link disconnect box500, a standoff adapter plate590may be used. Standoff adapter plate590has a relatively tall profile, which, as shown inFIG. 16, provides adequate room for a lineman to install mounting bolts599when connecting the link disconnect box500to existing terminal5of the network protector. Preferably, the standoff height H of adapter plate590exceeds the length of mounting bolts599so that mounting bolts599may be easily inserted between existing terminal5of the network protector and the first face591that bolts onto bottom terminal plate562of link disconnect box500. The standoff height H may be measured, for example, from the bottom surface of first surface591that contacts bottom terminal plate562and second surface592that contacts the existing terminal5of the network protector. Preferably, the standoff height H is greater that 1 inch, more preferably still between 2.5 and 2.5 inches, more preferably still from 1.75 to 2.0 inches.

Those skilled in the art will recognize that the present invention has many applications, may be implemented in various manners and, as such is not to be limited by the foregoing embodiments and examples. Any number of the features of the different embodiments described herein may be combined into a single embodiment, the locations of particular elements can be altered and alternate embodiments having fewer than or more than all of the features herein described are possible. Functionality may also be, in whole or in part, distributed among multiple components, in manners now known or to become known.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention. While there has been shown and described fundamental features of the invention as applied to being exemplary embodiments thereof, it will be understood that omissions and substitutions and changes in the form and details of the disclosed invention may be made by those skilled in the art without departing from the spirit of the invention. Moreover, the scope of the present invention covers conventionally known, future developed variations and modifications to the components described herein as would be understood by those skilled in the art.