GB2487009A - Fuse holder - Google Patents

Abstract

A fuse holder for use in electrical distribution apparatus is disclosed that is capable of being more safely replaced in a live circuit, in order to allow for circumstances in which a contractor erroneously does so. Improvements include: a conduit (116, Figs 2, 4, 6 & 8) for receiving a Rogowski coil; fixing the fuse contacts to conductors that engage with the busbar rather than a direct connection; a skirt (118, Fig 5) around the contacts to shield the operator from "arc eye" when connecting the fuse holder to the outlet (10); a handle 122 that can be used to insert the fuse holder and also to engage a clamp to secure the contacts 112 in place; a two-part, removable housing for the fuse holder (see Fig 6) to allow for repair if problems should arise; and an interlock (Figs 8 & 11) to prevent operation of the clamp until the fuse holder is home.

Description

Fuse Holder

FIELD OF THE INVENTION

The present invention relates to a fuse holder, for use in electrical distribution equipment.

BACKGROUND ART

Current forms of electrical distribution apparatus comprise a local transformer that will convert an incoming high voltage power feed to a low voltage three-phase supply suitable for local distribution. In this context, "low voltage" means a supply in the 400-600V (RMS) range at (typically) 800 to 1600 amps or higher.

A single transformer will generally feed a number of local circuits (or a single larger building with several circuits). Some means of isolating and protecting each circuit is therefore necessary. To date, the applicants have supplied the "Trifca", a fused distribution cabinet that is mountable on the transformer itself and accepts an incoming three phase low voltage supply which is then distributed to between 2 and 6 outgoing three phase circuits. Each phase of each circuit has an associated fuse holder to provide both protection and isolation; each fuse holder can be disconnected to change the fuse and/or isolate that phase of that circuit.

The fuse holders each comprise an insulating body which carries the fuse and which has a pair of projecting blades which can engage with corresponding blades within the distribution cabinet. Each projecting blade has a clamp which can be tightened via an insulated bolt head accessible from the front of the fuse holder; this operates a cam which draws the two blades together to provide the necessary quality of electrical connection.

Thus, to replace a fuse holder and make a connection, the holder must be inserted over the cabinet blades with the clamp in place either side thereof, and then the bolt head rotated to clamp the blades together. This should not be done while the circuit is live; if it is, then as the conductors approach there is a distinct risk of an arc forming which, if contact is not made quickly enough, could spot-weld the two conductors in an incorrect position. Such arcing is in any case inherently undesirable, as is causes "arc-eye" (temporary blindness) on the part of the operator, and it means than an operator cannot withdraw the fuse holder in order to correct the alignment as this will extend the arc with potentially hazardous consequences. Such arcs also generate explosive gases, which is clearly undesirable in confined areas.

Generally, it is forbidden to connect a fuse to a cicuit while that circuit is live. However, there are strong commercial pressures to replace such fuse holders without disconnecting the live supply. When the supply from the transformer is disconnected, all its outgoing circuits will be disconnected, not just the circuit whose fuse is to be replaced. Generally, during maintenance and repair work only one circuit will have been disconnected, whereas the others will still be live. Electrical suppliers are required to give prior notice of disconnections, to allow consumers time to protect electrical equipment such as IT infrastructure and/or make preparations for the loss of power. This is time-consuming and inconvenient, purely in order to replace a fuse. Contractors may also forget, and erroneously replace a fuse into a live circuit.

SUMMARY OF THE INVENTION

The present invention seeks to provide a fuse holder for such a distribution cabinet that is capable of being more safely replaced into a live circuit. This will allow for circumstances in which a contractor erroneously does so, and may clear the way for regulations to be eased in the future. A number of different improvements in the design of such a fuse holder are set out in this application, as follows.

In a first aspect, therefore, the present invention provides a fuse holder comprising a housing, a pair of electrical contacts within the housing, a fuse arranged across the contacts to define an electrically conductive path, and a conduit provided within the housing, extending from an external wall of the housing around the electrically conductive path and returning to an external wall of the housing. Such an arrangement permits a Rogowski coil to be safely passed around the electrically conductive path in order to monitor the current being carried by the fuse holder prior to disconnection. This allows the operator to confirm that the fuse holder is properly disconnected prior to removing it, and/or allows the operation of the circuit controlled by that fuse holder to be monitored such as for load balancing purposes.

It is convenient for the conduit to extend around and (indeed) to substantially encircle the fuse rather than any other part of the electrically conductive path. The conduit can return to the same external wall that it extends from, preferably to a location adjacent to the location from which it extends, to allow for a full encircling of the conductive path and to make the mode of operation of the coil and conduit clear to an operator.

In a second aspect, the invention provides a fuse holder comprising a housing, a pair of electrical contacts within the housing, a fuse attached to the contacts via an attachment means, and a contact face on the electrical contact, the contact race being spaced along the length of the contact from the attachment means. At present, in such ruse holders the fuse is typically retained via a single bolt that both holds the fuse to the contact and also provides the clamp which holds the contact in place once fitted. By separating these, tolerances in the fitting of the fuse do not affect the ease of insertion of the fuse holder into place. This, in turn, allows for a smoother and more reliable fitting process which is therefore safer.

The attachment means can be an aperture in the electrical contact, through which a conductive member such as a bolt or other threaded member passes in order to secure the fuse in place. The corresponding nut is preferably captive in order to prevent accidental loss.

In its third aspect, the invention provides a fuse holder comprising a housing, a pair of electrical contacts within the housing, a fuse arranged across the contacts, the housing comprising a front face and a skirt extending back from the front face by an extent greater than the electrical contacts. Thus, if the fuse is accidentally fitted while the circuit is live, the operator's eyes will be shielded from any arc that is produced by the skirt thereby preventing "arc-eye".

This will permit operators to actually look at what they are doing while fitting the fuse holder.

In this aspect, the invention also provides an electrical distribution apparatus comprising a separable fuse holder as defined above, at least one fuse socket for receiving the fuse holder, the fuse socket comprising a pair of socket electrical contacts for contact with the electrical contacts of the fuse holder, and a socket skirt around the socket electrical contacts, the fuse holder skirt and the socket skirt being sized so as to nest one within the other. This will provide a more complete shielding of the operator's eyes. We prefer that the socket skirt extends further than the socket electrical contacts; both will ideally extend sufficiently far that they nest one within the other before the fuse holder electrical contacts contact the socket electrical contacts. Generally, it is more convenient for the socket skirt to nest inside the fuse holder skirt, as this assists in aligning the two.

The fourth aspect of the invention provides a fuse holder comprising a housing, a pair of conductive contacts within the housing with an associated clamp for urging the contacts into an electrical contact, a fuse arranged across the contacts, and a handle located on a front face of the housing and connected to the clamp, the handle being moveable from a first position in which the clamp is released to a second position in which the clamp is engaged.

Such an externally accessible handle for closing the clamps allows this step to be carried out much more quickly and smoothly. At present, this requires a tightening tool to engage bolt head-type formations on the exterior of the fuse holder in order to rotate them and thereby cause the clamp to close.

This is slow, and requires accurate placement of the tool which may be difficult in adverse conditions. Both factors mitigate against the swift clamping of the contacts that is advisable in order to prevent arcing and welding of the contacts if the circuit is live.

It is preferably for the direction of movement of the handle from the first position to the second position to be (at least initially) transverse to the direction in which the contacts extend. Then, if the handle is also being used to carry the fuse holder, it can be inserted in one straightforward movement in which the handle (and fuse holder) is pressed forward into the relevant socket, and then the handle is moved transversely to clamp the contacts, without risking operation of the clamp during insertion of the fuse holder.

In its fifth aspect, the invention provides a fuse holder, comprising a housing having a front face and an opposing rear face, a pair of conductive contacts disposed within the housing and accessible via a contact aperture in the rear face of the housing, a fuse arranged across the contacts, wherein the housing is formed of at least two housing parts joined along a line that extends from the contact aperture via the front face. From time to time, errors will be made and the fuse holder will become welded in an incorrect orientation. It will then be necessary to remove the fuse holder. An ability to dismantle it will assist in this regard.

The front face of the housing will usually be where the handle is located.

The two housing parts are preferably secured together by fixings that are accessible via the front face, so that they can be removed easily.

Finally, the sixth aspect of the present invention relates to a fuse holder comprising a housing, containing at least two electrical contacts and a fuse bridging the two contacts, each contact incorporating a clamp for securing the respective contact against an external contact, a handle for actuating the clamp, moveable between a first position in which the clamp is released and a second position in which the clamp is engaged; and a latch located so as to be urged from a first default position to a second position on fitment of the fuse holder to a circuit, the latch being adapted to prevent movement of the handle from its first position to its second position when the latch is in its first position.

This builds on the fourth aspect discussed above, in which it was explained that an initially transverse movement of the handle allows for the fuse holder to be inserted and the clamp closed by way of separate actions that are unlikely to be confused. This aspect of the invention adds a positive interlock action that will serve to prevent the handle being actuated to close the clamp before the fuse holder is in the correct position.

This could be used to provide a fuse holder whose handle moved in the same direction as that in which the fuse holder moves during insertion, but we prefer to separate these actions and provide a resilient fuse holder.

The latch can comprise a hook formation arranged to interfere with movement of the handle from the first position to the second position, when the latch is in the first position. Likewise, the handle can comprise a hook formation arranged to engage with the hook formation of the latch. The hook formation can conveniently be located on the housing.

Alternatively, the latch can comprise a plunger within the fuse holder, biased toward a locking position, disposed so as to be forced into a non-locking position by contact with a part of the housing. This plunger can be disposed within the handle, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; Figure 1 shows an exploded view of a fuse holder according to the present invention, in place over a distribution cabinet outlet; Figure 2 shows the exploded fuse holder (etc) of figure 1, rotated; Figure 3 shows the distribution cabinet outlet; Figure 4 shows a view of the underneath of the fuse holder; Figure 5 shows the fuse holder positioned over the cabinet outlet, ready to fit; Figure 6 shows the fuse holder in an exploded form; Figure 7 shows the operative parts of the fuse holder without the housing thereof; Figure 8 shows a section through the fuse holder; Figure 9 shows a section through the fuse holder in the process of being fitted onto a cabinet outlet; Figure 10 shows a section through the fuse holder in the process of being fitted onto a cabinet outlet, showing the electrical contacts; Figure 11 shows a section through the fuse holder in place and locked onto an outlet; Figure 12 shows a section through the fuse holder in place and locked onto an outlet, showing the electrical contacts; and Figures 13 to 15 show sequential steps in the closing and locking process of an alternative embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to figures 1 to 7, these show a distribution cabinet outlet generally designated as 10 beneath an exploded fuse holder generally designated as 100. The distribution cabinet outlet 10 will generally be one of a two dimensional array of such outlets, usually arranged as 3 outlets in a specific direction, one for each phase of the 3 phase supply, and a variable number in the tranverse direction depending on how many outlets the specific fuse panel contains. For simplicity, only a single distribution cabinet outlet 10 is shown in these figures. Each outlet consists of a live contact 12 which is connected to the relevant supply phase from the transformer, and a switched contact 14 which leads to the relevant outgoing cable -which may be one of three such cables in case of a 3 phase supply or the single live conductor of a single phase supply.

The purpose of the fuse holder is to provide a removable fused connection between the live contact 12 and the switched contact 14, so as to allow for disconnection of the circuit connected to the switched contact 14 during maintenance work and to provide protection of that circuit during operation. The contacts 12, 14 are located in a recess 16 which is defined by a four-sided shroud 18, defined by four upstanding walls surrounding the recess 16 in which the contacts 12, 14 are located.

Space is provided within the shroud 18 to allow for insertion of a standard KelmanTM testing device, and the contacts 12, 14 are spaced and shaped to be compatible with such a device.

The fuse holder 100 consists of an external housing defined by a pair of housing sections 102, 104 which fit together to define an interior space 106 and a skirt 108. The skirt 108 is sized to fit around the shroud 18, and is very slightly flared outward so as to assist in guiding the fuse holder 100 over the shroud 18. As the user fits the fuse holder 100 to a chosen outlet 10, the shroud 18 and the skirt 108 interact through the very slight flare of the skirt 108 so as to guide the fuse holder 100 into the exact correct location relative to the contacts 12, 14.

Within the fuse holder 100, there is a fuse 110 of a suitable rating, which is of a generally barrel-shaped profile with a pair of parallel contacts projecting from either end of the barrel. Each contact pair is spaced to accept a conductor and (together with the conductor) include a through-hole allowing them to be bolted securely to the conductor via bolts 132, 134. Thus, two U-shaped conductors 112, 114 are also provided within the fuse holder 100; each connects to an end of the fuse 110 at one end of the U shape, whilst the other end of the U is located to mate with the contacts 12, 14 of the outlet 10. Thus, the fuse is positioned to one side of the contacts 12, 14 when the fuse holder 100 is in place.

This arrangement does mean that the fuse can be replaced easily by simply removing the two bolts 132, 134 and replacing the fuse 110. Only a spanner of the appropriate size is required.

A circular-section conduit 116 is provided, and extends from an aperture 118 on the housing section 102, around the fuse 110, and back to a further aperture 120 at a different location on the housing section 102. This allows a Rogowski coil 117 to be threaded around the fuse, to measure the current flowing through the fuse holder 100. Such measurements are useful in fault-finding and in load balancing. In contrast with existing arrangements, the Rogowski coil can be fitted without the need to remove any protective covers or expose any live conductors.

A handle 122 is provided on the fuse holder 100, in the form of a transverse bar that is rotatable from a raised position (illustrated) to a closed position in which the bar is adjacent the housing section 102. Cams within the fuse holder 100 are operated by movement of the handle 122 to the closed position, and act to clamp the conductors 112, 114 to the contacts 12, 14.

Test apertures 124, 126 are provided on the front of the housing section 102, to allow insertion of standard test plugs. These apertures are positioned directly over the central portion of the U-shaped conductors 112, 114 so that the tip of a test plug inserted into the apertures makes contact with the conductor to allow testing of the circuit voltage and the fuse continuity. An aperture 128 is also provided for a standard Litton yearn connector 130, i.e. a cable permitting power to be provided to the circuit temporarily from an external source, such as from a generator during repair work on the transformer or on only one output.

We explained above that one problem that arises from the inadvertent connection of a fuse holder while the relevant circuit is live is that of "arc-eye", i.e. a temporary blindness on the part of an operator exposed to sight of an arc between the live contact 12 and the conductor 114. Tn this embodiment, the shroud 18 and the skirt 118 are sufficiently long (or deep) that they begin to overlap shortly before the electrical conductors become close enough for an arc to form. Thus, in the event that an arc is struck, there will be a visual shield between the arc and the operator's eyes. This will then serve to prevent arc-eye. A result of this is that an operator is therefore free to look at the items he or she is operating; current procedures call for the operator to look away if there is a risk that the circuit is live, which in fact tends to exacerbate the risk of an arc for the very simple reason that the operator cannot move the fuse holder as accurately if they cannot look.

Further, as is clear from figure 7, the bolt retaining the fuse 110 in place on the conductors 112, 114 is no longer involved in clamping the conductors 112, 114 onto the contacts 12, 14. Tn prior designs, this bolt passed through the fuse contacts and a cam-wedge; to fit the fuse, the equivalent of the contact 12 or 14 was inserted between the blades of the fuse. The cam-wedge was then operated and the fuse contacts would (in theory) be clamped onto the contact.

Tn practice, this required the bolt to be tightened to within an acceptable range; if insufficiently tight, the cam would not be able to provide a clamping force, although it would appear to be tight to an operator. If too tight, the fuse blades would be brought together allowing insufficient space for the contact, Figures 8 to 12 illustrate the process of connecting the fuse holder 100 to the outlet 10 and clamping it in place. Figure 8 shows the fuse holder 100 ready to attach to the outlet 10. A fuse 110 is present, and has been bolted to the conductors 112, 114 via bolts 132, 134. The handle 122 is in the open or upper position. As can also be seen in figure 10, a section in a vertical plane spaced behind the vertical plane of figure 8, this mean that a cam link arm 136 connected to the handle 122 via a crank 138 has been moved downwards and into the fuse holder 100. This holds a cam 140 in a rotational position of minimum width and also cranks forward a cam plate 142. The cam plate 142 is on the end of a cam rod 144 which passes through an aperture in the conductor 112. Thus, by cranking the cam plate 142 forwards, it is urged away from the conductor 112.

The fuse holder 100 is then placed over the outlet 10; figure 9 shows it almost (but not quite) home. The positions of the various elements within the fuse holder 100 and the outlet 10 is such that the contact 14 will then sit between the conductor 112 and the cam plate 142. Figure 12 shows the fuse holder 100 fully home on the outlet 10 and with the handle 122 closed. Closure of the handle 122 rotates the crank 138 and hence draws the cam link arm 136 upwards. This rotates the cam 140; this both pulls the cam rod 144 and the cam plate 142 towards the conductor 112 thereby urging the trapped contact 14 towards the conductor 112, and also rotates the cam 140 so as to present a larger width in the space between the conductor 112 and the overlapping skirts 18, 108. This larger width is slightly oversized for the available space, and therefore the cam 140 urges the conductor 112 towards the contact 14. In this way, closing the handle 122 forces the conductor 112 and the contact 14 into a close and secure electrical contact.

An identical arrangement is provided for clamping the other conductor 114 and the other contact 12. Thus, once the fuse holder 100 is in place over the outlet 10 and the handle 122 closed, the necessary electrical connections will be made from the contact 12 via the fuse 110 to the switched contact 14. It will also be immediately obvious whether the handle 122 is raised or lowered and hence whether the clamps are secure or not. This contrasts with the known arrangements, where it is not immediately obvious whether the necessary rotation of the cam screws has been completed, and (as described above) even when this has been done it is still possible that the clamps are not secure.

If the handle 122 is closed prior to fitting the fuse holder 100 in place over the outlet 10, then the gap between the conductor 112 and the cam plate 142 will be narrowed, and this is likely to make it difficult to fit the contact 14 between them. This is likely to delay or hinder fitting of the fuse holder 100 in place, which can be expected to prompt the formation of an arc if the circuit happens to be live. That, in turn, will prevent withdrawal of the fuse holder 100 for fear of extending the arc, and would mean the fuse holder 100 would have to be held in place until either the fuse 110 (or another fuse) blew or a colleague was able to isolate the circuit. In either case, there would be sufficient time to spot-weld the conductor 112 to the contact 14.

This is obviously undesirable. The illustrated fuse holder is therefore designed to overcome this in two ways. First, premature closure of the handle 122 is inhibited by an interlock mechanism. Second, in the event that the fuse holder welds itself in place, it is easy to dismantle and thereby remove from the outlet 10. We will deal with these in turn.

First, the interlock mechanism. Referring to figures 8 and 11, a pair of interlock latch 146 are provided to restrain the handle 122 from closing until the fuse holder 100 is fully home (or nearly so) on the outlet 10. One interlock latch 146 is provided on each side of the fuse holder 100; figure 8 shows one latch 146 but there is a substantially identical latch on the other lateral side of the fuse holder acting in the same way on the corresponding other end of the handle 122. In practice, a single latch (or more than two latches) could be provided, but we find that two latches 146 provides a symmetrical action.

Each latch 146 is of an elongate convoluted shape comprising a hook 148 at one end which engages with a corresponding hook 150 on the handle 122 to restrain the handle 122 from being closed. Further along the latch 146, a horn 152 is provided to provide a fulcrum about which the latch can rotate when urged against an upper internal wall 154 of the fuse holder 100. A finger 156 extends away from the fulcrum 152 towards the open base of the fuse holder 100, and is shaped to confirm to the upper edge of the spatially corresponding part 158 (fig 11) of the outlet 10.

As the ruse holder 100 is fitted on the outlet 10, part 158 of the outlet 10 comes into contact with the end of the finger 156 and urges it upwardly, i.e. into the fuse holder 100. This causes the fulcrum 152 to make contact with the upper internal wall 154 of the fuse holder 100; with the outlet 10 urging the end of the finger 156 still further upwards, this forces the latch 146 to rotate about the fulcrum 152, which begins to draw the latch hook 148 out of engagement with the handle hook 150. This movement of the latch 146 continues to the point shown in figure 11, in which the latch 146 is forced into a fully withdrawn position, in which the finger 156 abuts the part 158 of the outlet 10 and is held there in conformity to the external shape of the outlet 10.

In this fully withdrawn position, the latch hook 148 is withdrawn to allow the handle 122 to be closed as shown. If the fuse holder is a few millimetres away fro being fully home, at which point the contacts 12, 14 will already be in place, then the handle hook 150 will just brush past the latch hook 148. Prior to that point, the latch hook 148 will engage with or obstruct the handle hook 150 and prevent closure of the handle 122.

With the handle 122 closed, the fuse holder will of course be held in place on the outlet 10 by the clamping force between the contacts 12, 14 and conductors 112, 114.. Thus, to fit and remove the fuse holder a straightforward series of movements is enforced; with the handle 122 open, the fuse holder 100 is fitted in place and the handle 122 is closed. To remove the fuse holder 100, the handle 122 is lifted, releasing the clamps, and the fuse holder 100 is withdrawn.

In addition, the fuse holder 100 is designed to be easily dismantleable in the unlikely event that it should become spot-welded to the contacts 12, 14.

This is achieved by forming the shell of the fuse holder 100 in two separate sections 102, 104 that are held together by fixings such as screws that are accessible from the front face of the fuse holder 100. Thus, if the fuse holder should become fixed in place and impossible to remove normally, the screws can be removed allowing the two parts 102, 104 to be separated.

The join line between the two parts 102, 104 splits the fuse holder 100 at the point from which the handle 122 extends. Therefore, once separated, the two parts can be withdrawn from either side of the handle 122 leaving the operative parts of the fuse holder 100 in place. These can then be chiselled off the outlet 10 in a generally known manner, to release the remains of the fuse holder 100.

Figures 13 to 15 show an alternative and preferred embodiment in which the manner of latching the fuse holder 100 to the base 10 is improved upon.

Figure 13 shows the fuse holder 100 nearly in place on the base 10, with about 4.5mm of movement still left. The handle 122 is fully open, and (in this embodiment) includes a spring loaded plunger 200 that, with the handle 122 in the fully open position, is disposed vertically and urged by the spring 202 downwardly out of a bore 204 in the handle 122 and through a slightly narrower hole 206 in a lower face of the fuse holder 100. A stop on the outer face of the plunger 200, set back from the very tip of the plunger 200, is too wide for the hole 206 and therefore prevents the plunger 200 from exiting the bore 204 any further.

This engagement of the plunger 200 with the hole 206 in the fuse holder serves to prevent the handle 122 from being closed while the fuse holder is remote from the base 10. In the position shown in figure 13, i.e. with about 4.5mm of travel still remaining, the tip of the plunger has just began to contact an upstanding post 208 on the fuse holder 10, located directly below the hole 206. This has a narrow tip 210 able to project into the hole 206, which (as shown in fiure 13) has just contacted the lower extremity of the plunger 200.

Figure 14 shows the fuse holder 100 fully home on the base 10, having travelled a further 4.5mm. The tip 210 of the post 208 has entered the hole 206 and forced the plunger 200 back into the bore 204 against the spring 202, displacing it from the hole 206. This means that the handle 122 is now free to rotate into a closed position.

That closed position is shown in figure 15. The hook 150 of the handle 122 now engages within an aperture 212 in the post 208, preventing the fuse holder 100 from being removed from the base 10 without first opening the handle.

In this way, a fuse holder 100 is provided that is safe against inadvertent (or deliberate) fitting to a live circuit, both in terms of the ease of fitting, the protection of the operator from arc-eye or other hazards, and in the ease of removal should there be difficulties.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.

This and another co-pending application are divisional applications in respect of prior application 0806990.8, published as GB2464911. They describe subject-matter that is claimed in GB2464911, and claim subject-matter that is described in GB2464911.

Claims (8)

1. CLAIMS1. A fuse holder, comprising; a housing, a pair of conductive contacts within the housing, having an associated clamp for urging the contacts into an electrical contact, a fuse arranged across the contacts, and a handle located on a front face of the housing and connected to the clamp, the handle being moveable from a first position in which the clamp is released to a second position in which the clamp is engaged.
2. 2. A fuse holder according to claim 1 in which the contacts both extend in a defined direction, and the direction of movement of the handle from the first position to the second position is at least initially transverse to the defined direction.
3. 3. A fuse holder comprising; a housing, containing at least two electrical contacts and a fuse bridging the two contacts, each contact incorporating a clamp for securing the respective contact against an external contact, a handle for actuating the clamp, moveable between a first position in which the clamp is released and a second position in which the clamp is engaged; and a latch located so as to be urged from a first default position to a second position on fitment of the fuse holder to a circuit, the latch being adapted to prevent movement of the handle from its first position to its second position when the latch is in its first position.
4. 4. A fuse holder according to claim 3 in which the latch comprises a hook formation arranged to interfere with movement of the handle from the first position to the second position, when the latch is in the first position.
5. 5. A fuse holder according to claim 4 in which the handle comprises a hook formation arranged to engage with the hook formation of the latch.
6. 6. A fuse holder according to claim 4 or claim 5 in which the hook formation is located on the housing.
7. 7. A fuse holder according to claim 3 in which the latch comprises a plunger within the fuse holder, biased toward a locking position, disposed so as to be forced into a non-locking position by contact with a part of the housing.
8. 8. A fuse holder according to claim 7 in which the plunger is disposed within the handle.