GB2467680A

GB2467680A - Cover for fuse housing

Info

Publication number: GB2467680A
Application number: GB1008200A
Authority: GB
Inventors: Thomas W Mennell
Original assignee: Schneider Electric Ltd
Current assignee: Schneider Electric Ltd
Priority date: 2008-03-13
Filing date: 2008-03-13
Publication date: 2010-08-11
Anticipated expiration: 2028-03-13
Also published as: GB2458298B; GB2467680B; GB201008200D0; GB2458298A; GB0804606D0

Abstract

A cover 10 for a housing at least partially encloses a pair of terminals, between which an electrically conductive device is connected. The combination of the cover and the housing together prevents access to the terminals and the electrically conductive device, and the cover comprises at least one socket 24 for connecting a measurement device to one of the terminals. The electrically conductive device can be a fuse (fig 2, 16). The socket 24 can be a 4mm socket for a banana plug and connected to the terminal via a fuse in a fuseholder 22. The cover may also comprise a guidance means (fig 2, 14) which allows a current measurement probe such as a rogowski coil to surround the conductive device. The cover allows electrical parameters of live electricity distribution components to be measured, while ensuring that the live components remain fully shielded.

Description

COVER

The present invention relates to a housing for an electrically conductive device, and in particular to housings that allow measurements of the electrically conductive device to be taken while the device is in use.

An important part of the distribution of electricity to consumers, for example residential, retail or commercial properties are Low Voltage (LV) distribution units. Here the reference to LV is in the context of electricity distribution and as such the voltage is usually at least mains voltage (400/230 V in Europe) and the components used in the units are typically rated higher than this, for example 660 V. The LV distribution units contain switchgear and other components to distribute electricity to consumers.

Historically, the distribution units were open and contained easily accessible terminals between which current carrying components were connected. If it was desired to measure electrical parameters of a live component in use, simple clip-on devices could be used.

Stricter health and safety legislation in the UK and elsewhere has since required that all live conductors and components are fully shielded to prevent accidental contact with live parts. In response to this requirement fully shielded distribution boards and components have been developed. For example, boards providing fully shielded conductors and components have been commercially available since 1985 from Merlin Germ.

Although fully shielded designs have much improved safety, their design restricts access to the live components, making measurements on live components difficult. Several solutions to this problem have been proposed, although none is entirely satisfactory. In some distribution units permanent instrumentation is included in the unit itself, providing a continuous measurement of, for example, current and load. However, this is expensive, particularly as such measurements may never be needed for some circuits and, even if they are needed, are only likely to be required rarely.

Where instrumentation is not provided in the board itself, it may be possible to take measurements on the cable bundle where it enters the board. However, this very much depends on the installation of the feed to the board. It can be difficult to identify which particular conductor feeds which circuit and in some cases access to the individual conductors is impossible.

The present invention provides means of accessing a live, shielded conductor or component to allow a measurement to be taken while it is in use.

According to a first aspect of the present invention, there is provided a housing for at least partially enclosing an electrically conductive device. The housing comprises guidance means positioned so that, when an electrically conductive device is at least partially enclosed within the housing, the guidance means defines a track for receiving a measurement probe, such that a measurement probe can at least partially encircle the electrically conductive device without touching the electrically conductive device.

The guidance means can be anything suitable for guiding a measurement probe. For example, in one embodiment it can be a track or channel for guiding an elongated flexible measurement probe. The housing can be used with any electrically conductive device, for example a conductor or an electrical component. In various embodiments of the invention, the housing could be a cable track or part of an LV distribution board, such as a fuse holder. A typical measurement probe for use with the invention will have an elongated flexible probe portion that can be guided around the device by the guidance means, and is preferably a probe for measuring current. Such probes are commercially available, for example devices using a Rojowski coil.

By providing the guidance means, a probe can be used to measure the electrically conductive device in use while the device itself is shielded. The guidance means ensures that the probe is guided without coming into contact with live components. The present invention avoids the expense of dedicated measurement instrumentation and the inconvenience and difficulty of making measurements on conductors before they enter a distribution board. A further advantage is that the guidance means can be incorporated into a housing without any significant change in overall dimensions, allowing retro-fitting to existing apparatus, and enabling a compact design to reduce the space taken up and use less natural resources in manufacture.

By providing the guidance means in the housing, it can be easily retrofitted to existing shielded conductors, components and distribution boards. All that is required to be changed is the housing.

When the housing is for use with removable electrical conductive devices, it may be adapted to at least partially enclose at least one pair of terminals. In use, the electrically conductive device is connected between the pair of terminals.

The guidance means may be curved, allowing it guide a measurement probe smoothly.

Preferably, the guidance means follows the path of an arc of a circle and is more preferably semi-circular.

The guidance means may be an elongated hollow body open at both ends. The hollow body defines a passage for a measurement probe. The hollow body could be tubular or have a constant cross section along its length.

According to another aspect of the present invention, there is provided an assembly for enclosing an electrically conductive device connected between two terminals. The assembly comprises a housing as described above and a cover. In use the housing and the cover together prevent access to the terminals and the electrically conductive device, providing shielding, but allowing access to the guidance means so that measurements can be taken. Where the invention is retro-fitted to an existing installation, the cover of the assembly may be the cover used in the existing installation.

The cover may further comprise at least one socket for connecting a measurement device to one of the terminals. The socket allows access to the terminals when the cover is in place. Preferably a socket is provided for each socket allowing measurements to be taken across the device, such as voltage. The combination of the socket and guidance means allows measurements of all parameters that may be required, some examples are current, power, power factor, harmonic content and KVA.

In another aspect of the present invention, a cover for an electrically conductive device is provided without a housing containing guidance means. In use, the electrically conductive device is connected between a pair of terminals, and the cover comprises at least one socket for connecting a measurement device to one of the terminals.

In both of the above aspects, the socket is preferably connected to one of the terminals via a fuse. The fuse provides additional safety for the connection.

In one embodiment of the present invention, the electrically conductive device is a fuse.

In alternative embodiments of the invention, housings and assemblies may be provided for more than one electrically conductive device. For example, in one embodiment the housing could be for three fuses, one for each phase of a three-phase electricity distribution system.

In another aspect of the present invention, there is provided an electrical distribution board comprising at least one housing or assembly as defined above.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is an isometric front view of an assembly according to an embodiment of the present invention, with a portion cut away; Figure 2 is an isometric rear view of the assembly of Figure 1, with the same portion cut away; Figure 3 is a front view of the assembly of Figure 1; Figure 4 is a cross section of the assembly of Figure 1, along line A-A shown in Figure 3; Figure 5 is an isometric front view of a fuse cover according to an embodiment of the invention for use with the assembly of Figure 1; and Figure 6 is an isometric rear view of the fuse cover of Figure 5.

Figures 1 and 2 depict isometric front and rear views, respectively, of an assembly 2 according to an embodiment of the present invention. In both Figure 1 and Figure 2, the same portion has been cut away so that the internal construction according to the present invention can be seen more clearly. The portion has been cut away purely to enable the construction to be understood more clearly, there is no cut-out in the preferred embodiment.

The embodiment of Figures 1 and 2 is a three phase fuse assembly which forms part of an LV distribution board. The assembly 2 comprises a terminal rail 4, a housing 6, and three covers 8, 10, 12 -one for each phase. The terminal rail comprises three pairs of terminals 14 for connection to a conductive component, one for each phase. The housing 6 is positioned over and partially covering the terminal rail 4. The housing 6 defines three openings positioned above the terminals 14. A cover 8, 10, 12 is placed over each of these openings. Each cover 8, 10, 12 includes a fuse 16 for connection to the pair of terminals 14. In use the fuse 16 is connected to the terminals 14 when the cover 8, 10, 12 is in place.

The connection between the fuse 16 and the terminals 14 holds the cover in place. The combination of the housing 6 and the cover 8, 10, 12 acts as a shield which prevents access to live components. To allow easy removal of the cover 8, 10, 12 and the associated fuse, a handle is moulded into the cover, which can be seen most clearly in the view of cover 10 in Figure 2.

The housing 6 and cover 8, 10, 12 are made from plastic, or another insulating material.

To allow the current flowing through the fuse 16 to be measured while the fuse 16 is connected to the terminals 14, a guidance means, track or channel 18 is provided in the housing 6. The channel 18 follows a semi-circular path, is hollow along its whole length and has two open ends 20. The open ends 20 are positioned so that they are on either side of the cover 8, 10, 12 when a cover is in place. This can best be seen in the front view of Figure 3.

As can best be seen in the cross section of Figure 4, the channel 18 is positioned so that it does not contact the fuse 16 when the cover 8, 10, 12 is in place, providing electrical isolation from the fuse. It is preferred to manufacture the channel 1 8 from plastic or another insulating material, but a conductive material could also be used, providing that the channel 18 is spaced a sufficient distance from any live components so that the resultant air gap provides isolation.

As can be seen in Figures 1, 2 and 3, the construction of covers 8 and 12 is different from cover 10. Covers 8 and 12 have the same construction as fuse holders used in prior art distribution boards. Cover 10 includes additional sockets 22 for allowing the connection of measurement apparatus to the terminals 14, even though the terminals 14 are shielded within the assembly. Front and rear perspective views of the cover 10 can be seen in Figures 5 and 6, respectively.

A fuse holder 24 is provided next to each socket 22. The sockets 22 are connected to the fuse holder 24 which is in turn connected to a connection plate 26 which engages the terminal 14 when the cover lOis placed in the assembly. (The connections between the socket 22, fuse holder 24 and connection plate 26 are not shown in Figure 6, but can be provided by any suitably rated insulated conductor or wire.) Both the socket 22 and fuse holder 24 are positioned on the surface of the cover 10 that can be accessed by a user when the cover 10 is in place in the assembly 2.

The socket may be a standard 4 mm socket for a "banana" plug. The fuse holder receives a standard fuse for proving protection to a measurement device connected to the socket.

In use, if it is desired to measure the current flowing through fuse 16, a current sensing probe, such as a commercially available probe using a Rojowski coil, can be inserted through the channel 18. It can then encircle the fuse 16 to enable measurement of current.

Other parameters can be measured by connecting a suitable measuring device to the sockets 22. This enables measurement of power, power factor, harmonic content or KVA, amongst others.

The present invention therefore allows electrical parameters of live electricity distribution components to be measured, while ensured that the live components remain fully shielded.

There is no need for dedicated permanent instrumentation because access can easily be gained to make measurements on live components.

It will be appreciated that in alternative embodiments, the housing 6 could include channels 18 for some but not all of the components. The housing 6 may also be used with any combination of covers including additional sockets, or covers without additional sockets.

Although this embodiment has been applied to a three-phase fuse assembly, it will be appreciated that the concepts of the present invention can be applied to many other applications. For example, in alternative embodiments, the channel for receiving a measurement probe may be provided in a cable track, and the covers may hold electrically conductive components other than fuses.

Claims

CLAIMS1. A cover for a housing which at least partially encloses at least one pair of terminals, wherein in use at least one electrically conductive device is connected between the pair of terminals and the combination of the cover and the housing together prevents access to the terminals and the electrically conductive device, wherein the cover comprises at least one socket for connecting a measurement device to one of the terminals.
2. A cover according to claim 1, wherein the at least one socket is connected to one of the two terminals via a fuse.
3. A cover according to claim 2, further comprising a fuse holder for holding the fuse.
4. A cover according to claim 1, 2 or 3, wherein the electrically conductive device is a fuse.
5. A cover according to any one of the preceding claims, wherein the at least one socket is a 4 mm socket.
6. An electrical distribution board comprising at least one cover according to any one of the preceding claims.