Typical devices for the measurement of current flowing through a circuit rely upon disconnecting a power feed to the circuit, inserting a measurement device between the power feed and the circuit and then measuring the flow through the device. Such conventional devices can often prove problematical to set up as they require the breaking and making of a circuit in order to insert the device into the current feed.

Hereinafter, wherever the term"fuse"is used, it must be understood that this term is intended to mean any component which will only allow up to a rated current to flow through it and, if that rating is exceeded then the component will change from a closed condition to an open circuit condition. The term therefore encompasses normal fuses, resettable fuses and circuit breakers etc. such as may be used in a power feed line to protect a circuit from overcurrent conditions.

According to a first aspect of the invention, there is provided a device for monitoring an electrical property in an electrical circuit, the device comprising a pair of terminals for cooperating with end terminals of a fuse holder and arranged to take the place of an existing fuse; a current and/or voltage measuring device associated with the pair of terminals; and means for allowing said property to be monitored.

Preferably, the device includes fuse receiving means for receiving a fuse to protect the circuit.

Preferably, the device includes a data/power cable for conducting data and/or power from the device to an external monitoring means.

The device may be powered via the data/power cable or, may be powered by the circuit.

The device may comprise a main body portion connected to a data/power cable, the main body portion being arranged to receive a circuit protecting fuse therein, the body portion further comprising terminals which protrude from or are located on an external face of the housing for co-operation with end terminals of the fuse holder of the circuit.

The device preferably further includes a cover by which the fuse may be accessed to be replaced.

The electrical property may be current and the device may include a current sensor.

Said electrical property may be voltage and the device may include a voltage sensor.

Said electrical property may be power and the device may include voltage and current sensors

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a schematic view of a first embodiment of the device; Figure 2 is a schematic circuit diagram of the device of Figure l; and Figure 3 is a schematic diagram of a second embodiment of the device.

Referring now to Figure 1, there is shown an embodiment of the device comprising a first terminal 1 and a second terminal 2 for cooperation with an existing fuse holder of a circuit to be monitored, a main body portion 3 which houses current monitoring means and is arranged to receive a fuse 4 to be closed by a fuse cover 5. There is also shown a data/power cable 6.

In use, a fuse is removed from the circuit to be monitored and the device plugged in to the fuse holder by means of terminals 1,2. The fuse 4 may be the original fuse from the circuit, or may be one which is of suitable rating so as to protect the circuit during current monitoring.

It will be appreciated that there are many different means of measuring current and that any suitable means may be provided housed within the body portion 3. Alternatively, it is of course possible to convey

electrical signals to a remote device via terminals 1,2 and the data/power cable 6, so that actual current monitoring may be done remotely from the circuit to be monitored. As the device is to take the place of a circuit fuse, the device is aimed at the measurement of circuit current, but this measurement may be done in any conventional manner and may result in the device actually generating a device voltage proportional to the circuit current, or indeed a device current proportional to the circuit current.

Referring now to Figure 2, there is shown a simple schematic diagram of the internal workings of the device in which current flow to the circuit to be monitored enters through terminal 1, passes through a suitably rated fuse 4, and then into the circuit from the fuse 4 through terminal 2. A current sensor 7 of the device monitors the current in a non-invasive manner, has it's monitoring signal processed by electronics 8 and a voltage or current signal indicative of the current flow in the monitored circuit is thereafter sent to external monitoring means via cable 6.

Referring now to Figure 3, there is shown a second embodiment of the invention which is suitable for providing voltage and power measurements as well as current measurements.

The dveice of Figure 3 comprises first and second terminals 1,2, for cooperation with an existing fuse holder of the circuit to be monitored, a fuse 4 to protect the circuit to be monitored (taking the place of the original fuse removed from the fuseholder), a data/power

cable 6, a current sensor 7 and processing electronics 8 ( in the same way as the first embodiment). In addition, the Figure 3 embodiment includes connections 9 to the line voltage supply (+,-or live plus neutral) of the circuit to be monitored (which line supply also conveniently provides the device power), a voltage sensor 10 and voltage sensor output leads 11. The device is further preferably housed in a housing 3 of the type shown in Figure 1.

Operation of the device of Figure 3 is identical to that of the device of Figures 1 and 2, but further provides the capability of monitoring voltage of the circuit and hence also power consumption. The processing electronics 8 processing signals from the current sensor 7 and the voltage sensor 10 in a conventional manner to provide output signals representative of current, voltage power or power quality (or any combination thereof) via the data cable to an external monitor/display (not shown).

The advantages of the device of the present invention are that no rewiring needs to be done because the device can be simply and conveniently positioned by removing an existing fuse and putting terminals of the device in place of the fuse. Further, it can also be appreciated that the device may actually be used to determine a suitable fuse rating for an electrical circuit, with the device being tested under different load conditions, the current being monitored by a current sensor 7 and an acceptable tolerance then being set for determining a suitable fuse rating for the circuit.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.