WO2015024068A1

WO2015024068A1 - Expandable utility meter

Info

Publication number: WO2015024068A1
Application number: PCT/AU2014/000847
Authority: WO
Inventors: Zheng Zhu; Marcelo DE MARCO; Paul Collins; Justin Clifford MATTHEWS; Marcello Dominic CIRCOSTA; Keith Torpy; Ian Jackson DAVIS
Original assignee: Landis & Gyr Pty Ltd
Priority date: 2013-08-23
Filing date: 2014-08-25
Publication date: 2015-02-26

Abstract

An electrical utility meter base unit is disclosed in this specification. The base unit has an expansion interface that connects a removable expansion module to circuitry within the base unit. The expansion interface has an electrical coupling that provides a low impedance connection to an electrical distribution network and a separate data interface that transfers digital data between the base unit and expansion module

Description

EXPANDABLE UTILITY METER

Field of the invention

The present invention relates generally to utility metering systems.

Background of the invention

Electrical meters are used to determine the quantity of energy used by a consumer site (such as a household or industrial facility) . However, the functionality of utility meters has expanded over the last decade. Modern 'smart meters' are capable of communicating with remote monitoring systems (often managed by an electrical

utility) , determining the state of the localised

distribution network, manipulating the state of individual circuits at the consumer site and various other auxiliary functions that supplement conventional metering

operations . Summary of the invention

In a first aspect, the present invention provides an electrical utility meter base unit comprising:

a housing having a rear face that mounts to a support structure and an opposing front face with a display unit, metrology circuitry enclosed within the housing that monitors energy exchanged between a consumer site and an electrical distribution network,

a mains interface that connects the utility meter to a distribution network, the mains interface comprising a plurality of input terminals mounted to the base unit and electrically connected to the metrology circuitry,

a site interface that connects the utility meter to a local site network, the site interface comprising a plurality of output terminals mounted to the base unit and electrically connected to the metrology circuitry,

an expansion interface that connects an expansion module to circuitry within the base unit, the expansion interface having an electrical coupling that provides a low impedance connection to an electrical distribution network and a separate data interface that transfers digital data between the base unit and a mounted expansion module, and

a mounting interface accessible via the front face of the housing that supports an expansion module, the

mounting interface defining a mounting footprint for expansion modules that is bounded at an upper limit by the display unit, the mounting footprint being unbound forward of the housing.

In an embodiment, the electrical coupling and the data interface of the expansion interface are spatially separated to reduce electrical interference.

In an embodiment, the electrical coupling and the data interface of the expansion interface are spatially separated by more than 5cm.

In an embodiment, the mains interface and the data interface are spatially separated to reduce electrical interference, thermal interference and magnetic

interference .

In an embodiment, the mains interface and the data interface are spatially separated by more than 8cm.

In an embodiment, an extra-low voltage plate is disposed between the mains interface and the expansion interface .

In an embodiment, the base unit includes

communications circuitry mounted within the housing that exchanges data with communications networks external to the utility meter. In an embodiment, the base unit comprises a high current switch that is electronically controlled by circuitry within the base unit to electrically connect the mains interface with the site interface.

In a second aspect, the present invention provides a utility meter system comprising:

a base unit comprising a housing having a rear face that mounts to a support structure and an opposing front face, metrology circuitry enclosed within the housing that monitors energy exchanged between a consumer site and an electrical distribution network, and an expansion

interface that connects an expansion module to circuitry within the base unit, the expansion interface having an electrical coupling that provides a low impedance

connection to an electrical distribution network, and

a plurality of expansion modules that are configured to connect electrically to the base unit via the expansion interface, each of the expansion modules having a mating surface that seats adjacent the front face of the base unit and an opposing front panel that projects forward of the base unit housing,

the expansion modules having dissimilar volume, defined by the distance between the mating surface and front panel.

In an embodiment, the base unit includes a mounting interface that is accessible via the front face of the housing and supports an expansion module, the mounting interface defining a mounting footprint for expansion modules that is bounded at an upper limit by a display unit mounted within the housing adjacent the front face.

In an embodiment, a mains interface connects the utility meter to a distribution network, the mains interface comprising a plurality of input terminals mounted to the base unit and electrically connected to the metrology circuitry, and

a site interface connects the utility meter to a local site network, the site interface comprising a plurality of output terminals mounted to the base unit and electrically connected to the metrology circuitry,

In an embodiment, the expansion interface comprises an electrical coupling that provides a low impedance connection to an electrical distribution network and a separate data interface that transfers digital data between the base unit and a mounted expansion module.

interference .

In an embodiment, the base unit comprises a high current switch that is electronically controlled by circuitry within the base unit to electrically connect the mains interface with the site interface. In an embodiment, communications circuitry is mounted within the base unit housing that exchanges data with communications networks external to the utility meter. In a third aspect, the present invention provides a plurality of expansion modules that are configured to connect electrically to an electrical utility meter base unit via an expansion interface, each of the expansion modules having a mating surface that seats adjacent a front face of the base unit and an opposing front panel that projects forward of the base unit housing when mounted,

In a forth aspect, the present invention provides an electrical utility meter base unit comprising:

a housing,

metrology circuitry enclosed within the housing arrange to monitor energy exchanged between a consumer site and an electrical distribution network,

an expansion interface arrange to connect an

expansion module to circuitry within the base unit, the expansion interface having an electrical coupling that provides a low impedance connection to an electrical distribution network and a separate data interface that transfers digital data between the base unit and a mounted expansion module, the mains interface and the data interface are spatially separated to reduce electrical interference, thermal interference and magnetic

interference .

In a fifth aspect, the present invention provides an electrical utility meter base unit comprising:

a housing, metrology circuitry enclosed within the housing arrange to monitor energy exchanged between a consumer site and an electrical distribution network,

a mains interface arrange to connect the utility meter to a distribution network,

an expansion interface arrange to connect an

expansion module to circuitry within the base unit, the expansion interface having an electrical coupling that provides a low impedance connection to an electrical distribution network and a separate data interface that transfers digital data between the base unit and a mounted expansion module, and

wherein the mains interface and the data interface are spatially separated to reduce electrical interference, thermal interference and magnetic interference.

In a sixth aspect, the present invention provides an electrical utility meter base unit comprising:

a housing,

an expansion interface arrange to connect an

communications circuitry arrange to exchange data with communications networks external to the utility meter, the communications circuitry being mounted within the base unit housing. . Brief description of the Figures Embodiments of the invention will now be described, by way of example, with reference to the accompanying figures, in which:

Figure la is a perspective view of a utility meter comprising a base unit and an expansion module.

Figure lb is a front elevation of the utility meter depicted in Figure la.

Figure lc is a side elevation of the utility meter depicted in Figures la and lb.

Figure 2a is a perspective view of utility meter base unit illustrated in Figures la to lc.

Figure 2b is a front elevation of the utility meter base unit depicted in Figure 2a.

Figure 2c is a side elevation of the utility meter base unit depicted in Figures 2a and 2b.

Figure 3a is a front elevation of the utility meter depicted in Figures la to lc with the terminal cover removed to expose the expansion module interface.

Figure 3b is an exploded view of the expansion module interface disposed depicted in Figure 3a.

Figure 4 is a front elevation of the utility meter base unit depicted in Figures 2a to 2c with the terminal cover and extra-low voltage plate removed.

Figure 5 is a perspective view of the utility meter depicted in Figures la to lc with an alternate terminal cover .

Figure 6 is a schematic diagram of a communications network topology including multiple utility meters. Detailed description of the invention

An expandable electrical utility meter is disclosed in this specification. The meter comprises a base unit with a mounting interface for an expansion module. The base unit incorporates metrology circuitry for metering the energy exchanged between a consumer site and an electrical distribution network. It may also incorporate communications circuitry for exchanging data with communications networks external to the utility meter. The meter may be customised for particular applications by mounting an expansion module with additional capabilities. The mounting interface for expansion modules is disposed at the front of the base unit. The mounting interface is accessible via a front face of the housing to reduce obstructions (such as adjacent meters or wiring mounted within a shared electrical panel) . The depth of module that can be mounted to the base unit is not

constrained by the base unit housing (as depicted in

Figure lc) . This enables modules of various depths to be mounted to the base unit. Electrical utility meters are often mounted in close proximity with other instruments at consumer sites (typically within a utility panel) .

Alternatively, the electrical utility meter may be mounted on its own, but in a utility panel which provides

restrictive space. This reduces the space required to install the meter, but physically restricts the form- factor of utility meters after installation. Mounting the expansion module to the front of the meter alleviates this constraint. It also simplifies installation of the module as the mounting interface is readily accessible. The base unit has an expansion module interface that directly connects a module to the AC mains supply from the distribution network. Receiving AC voltage from the mains supply enables the expansion module to monitor

characteristics of the electrical distribution network (such as neutral line performance) and implement a 'power line communications' protocol for transmitting

communications signals to the electrical utility managing the distribution network. Extension modules may be used to expand the metering capabilities of the base unit (by functioning as a

supplementary metrology unit) , perform electrical diagnostic functions (monitoring the state of the

electrical distribution network) , interface with other devices at the consumer site (such as water meters, gas or smart appliances connected to a 'Home Area Network' ) or function as a field configurable extension to the base unit. The expansion module may also facilitate networking between compatible utility meters installed in close proximity. Utility meters can be organised in 'Floor Local Area Networks' (FLAN's) to reduce communications traffic in some situations (such as high density residential buildings) . A designated 'master' meter manages

communications for the FLAN by collating data from

individual 'slave' meters and transmitting the collated data from the FLAN to the electrical utility.

An embodiment of the expandable electrical utility meter is illustrated in Figures la to lc. The illustrated meter 1 is arranged to be electrically connected between an electrical distribution network (the mains supply) and a consumer site. Electrical energy is typically

transferred from the electrical distribution network to the consumer site for consumption. The consumer site may transfer electrical energy to the electrical distribution network in situations when energy generation at the consumer site exceeds consumption. The illustrated meter 1 has metrology circuitry, in this example a metrology module, that monitors the energy transfer between the consumer site and the electrical distribution network. The electrical utility meter 1 comprises a base unit

10 (illustrated in Figures 2a to 2c) and an expansion module 30. The base unit 10 performs primary metering functionality and is capable of installation without the expansion module 30. The circuitry comprising the

metrology module is integrated with the base unit 10 in the illustrated embodiment. The expansion module 30 is a removable component that extends the base units functionality. The base module 10 includes an expansion mount that receives the expansion module 30. The expansion mount is disposed at the front of the base unit 10 so that the depth dimension of the expansion module 30 is not restricted (i.e. the amount that the expansion module 30 extends from the front of the base unit 10) . The

illustrated base unit 10 and expansion module 30 have compatible electrical interfaces that enable the

respective components to be readily interconnected.

The base module 10 has a mains interface 53 (shown in Figure 4) where wiring from the electrical distribution network is terminated. The illustrated mains interface 53 comprises a plurality of high voltage terminals 54. The terminals 54 are electrically connected to the metrology circuitry. A site interface (not shown in the figures) connects the utility meter to a local site network. The site interface generally comprises a plurality of output terminals mounted to the base unit and electrically connected to the metrology circuitry. A high current switch electrically connects the mains interface 53 with the site interface. The high current switch is

electronically controlled by circuitry within the base unit (typically a microcontroller or similar processing unit) to make and/or break electrical connections with an expansion module.

The expansion module 30 derives AC power directly from the mains supply (i.e. the base unit does no rectify or regulate the power supplied to the module) through the base unit 10. This enables the expansion module 30 to monitor parameters of the electrical distribution network (such as neutral phase function) and utilise the supply lines for communication with the electrical utility (using 'power line communications' ) . The expansion module 30 may include a dedicated rectifier and/or regulator circuitry to process the electrical supply received from the

electrical distribution network.

The expansion module 30 is segregated from the mains interface 53 by an extra-low voltage (ELV) plate 45 in the illustrated embodiment (shown in Figure 3a) . The extra-low voltage plate 45 shields consumers/technicians from the high voltage terminals 54 where the mains supply is terminated. The base module 10 and expansion module 30 are typically both installed (terminated) by a qualified technician because both components are powered directly from the mains supply.

The mains interface and the data interface (the data connection between the expansion interface and an

expansion module) are spatially separated within the base unit 10 to reduce electrical interference. The distance between the respective interfaces is typically between 2cm and 10cm, although this may be restricted by the form factor and layout of the base unit 10. Ideally, the interfaces are separated by more than 2cm, and preferably more than 5cm. The approximate spacing of the electrical and data connectors may be (rounded to the nearest centimetre) 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm, 10cm.

The illustrated base unit 10 comprises a housing 11 that encloses the metrology circuitry. The housing has a rear face that sits adjacent a support structure (such as an electrical panel where the utility meter 1 is mounted) and an opposing front face that is accessible when the meter 1 is mounted. A removable terminal cover 14, 16, 17 mounts to the underside of the base unit to enclose the mains interface 53. The terminal cover 14, 16, 17 is accessible via the front face of the housing 11 to facilitate access to the utility meter wiring after installation. The configuration of the terminal cover 14, 16, 17 may be altered to reflect the configuration of the utility meter 1 (as illustrated in Figures la, 2a and 5) The utility meter 1 is illustrated in Figures 3a and 4 with the terminal cover 14, 16, 17 removed. The base unit housing 11 incorporates an interface panel 27 disposed at the front of the meter 1 above the extension mount. The interface panel facilitates

communication with a technician and external system (such as diagnostic tools) . The illustrated interface panel includes an optical port 20 (such as an infra-red

interface), hardware buttons 21, a display unit 22 (such as an LCD interface) and a dedicated user interface 23.

The illustrated base unit 10 is mounted to a

supporting structure (such as an electrical panel) using a mounting supports 13. The illustrated mounting supports 13 receives a mechanical fastener (such as screws, nails or bolts) . Other mounting arrangements (such as sliding dovetail joints and rails) may also be used. The base unit 10 has a rear face 15 with a mounting surface that is disposed adjacent the support when the meter 1 is

installed. The mounting surface typically sits flush with a support surface (such as a wall or backing surface of a panel) .

The base unit 10 includes an expansion interface 50 that electrically connects a removable expansion module 30 to circuitry within the base unit 10. The illustrated expansion interface 50 has an electrical coupling that provides a low impedance connection to an electrical distribution network . An expansion module may also use the electrical coupling to send and/or received AC signals via the electrical distribution network and enhance the metrology function of the electrical utility meter. A separate data interface transfers digital data between the base unit and a mounted expansion module. A mounting interface secures removable expansion modules to the base unit 10. The mounting interface is accessible via the front face of the housing 11. This enables installation and removal of expansion modules without dismounting the base unit or interfering with the mains interface 53 or base unit. The mounting interface defines a mounting footprint 55 for expansion modules. The mounting footprint 55 is generally bounded at an upper limit by the display unit 22. The base unit housing 11 also influences the form-factor of the expansion module mounting footprint. For example, the mounting footprint is typically contained within the overall footprint of the base unit 10 so that adjacent utility meters and space constrains within an electrical panel do not restrict expansion module installation. The base unit 10 does not restrict the mounting footprint forward of the housing 11 (i.e. the mounting footprint is unbound forward of the housing 11). The process for mounting an expansion module to the utility meter 1 depicted in Figure 4 comprises:

• removing the terminal cover 14 (the meter 1 is

depicted with the terminal cover 14 already removed in Figure 4 ) ,

· aligning the module slightly below (0.5cm) top of the mounting footprint 55,

• moving the module into contact with the front face of the meter, and

• sliding the meter upwardly to form electrical and

mechanical connections between the module and

expansion interface.

High voltage connection blades protruding from the

expansion module engage with tulip connectors in the base meter to form the electrical connection. A lip 56, disposed adjacent the top of the mounting interface footprint 55, and two fastening tabs disposed on either side of the mounting interface (not shown in the Figures) secure the expansion module adjacent the front face of the base unit 10. The fastening tabs engage with a reciprocal L-shaped tracks on the sides of the expansion module.

The base unit and expansion module are usually ^xsealed' after installation. The seal provides a visual tamper indication. Electrical utilities often use a wire with crimped metal tab or a single use plastic locking tab to seal utility meters.

The disclosed mounting interface supports expansion modules adjacent the front face of the base unit housing 11 away from the mains interfaces 53. The advantages of this mounting configuration include:

· meters can be shipped with modules already attached

(if the module was on located adjacent the mains terminals it need to be removed for installation and re-wiring) ,

• the distance between the mains interface 53 and

mounting interface promotes safer module installation and removal,

• the distance between the mains interface 53 and the expansion interface 50 reduces electrical

interference from the mains circuitry experienced by a mounted expansion module,

• the distance between the mains interface 53 and the mounting interface 50 reduces heat dissipation from the mains interface 53 (which commonly operates at higher current) to a mounted expansion module,

· the distance between the mains interface 53 and the expansion interface 50 reduces the likelihood of electrically coupled radiated noise interfering with devices on the mains circuit,

• the distance between the mains interface 53 and the mounting interface 50 reduces the effects of nearby metal work that can degrade the performance of antennas and magnetic devices in sensitive radio circuitry (the position of the mounting interface enables the development consistent magnetic

properties at the location where the expansion module mates with the meter) , and

· the distance between the mains interface 53 and the mounting interface 50 reduces interference with metrology circuitry that is disposed within the base unit 10 proximate to the mains interface 53. The illustrated expansion interface 50 has an

electrical coupling 51 that draws power from the mains connection 53 (active and neutral) and a separate data interface 52 (serial connector) . The electrical coupling 51 and data interface 52 are disposed adjacent diagonally opposed corners of the expansion interface. This maximises spatial separation for a given expansion module footprint 55. The expansion interface 50 provides a low impedance connection to the electrical distribution network. The electrical coupling is also capable of facilitating mains coupled signalling (with power line carriers) . The data interface 52 establishes a communications link between the base unit 10 and the expansion module 30.

The mains coupling and data interface 57 a spatially separated to reduce electrical interference. They are typically disposed adjacent diagonally opposed corners of the expansion interface. This maximises spatial separation for a given expansion module footprint 55. The distance between the electrical coupling and the data interface ranges between 2cm and 12cm, but is often restricted to less than 10cm to comply with the form-factor of the expansion interface. Ideally, the spacing between the respective interfaces is greater than 5cm, and preferably greater than 8cm. The approximate spacing of the

electrical and data connectors may be (rounded to the nearest centimetre) 1cm, 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm, 10cm, 11cm, 12cm. The expansion interface 50 is disposed adjacent the front face of the base unit housing (the illustrated interface 50 is covered by terminal cover in Figures 2a to 2c) . This simplifies expansion module installation. The expansion interface 50 is accessible via the front face of the base unit 10 to allow expansion modules to be mounted without interfering with the mains interface 53 wiring or base unit 10 mounting supports 13. The base unit housing 11 does not restrict the size of expansion module in a direction extending generally perpendicular to the rear face 15 and mounting surface.

The base unit 10 may be compatible with a plurality of expansion modules 30 that perform different functions. This enables the functionality of the utility meter 1 to be customised to reflect the demands of a consumer site. The positioning of the expansion interface 50 (at the front of the base unit 10) and configuration of the base unit housing 11 establish a flexible form-factor that accommodates modules with dissimilar depth dimensions (as depicted in Figure lc) . The depth of the expansion module 30 may be restricted to 150mm from the front surface of the base unit 10 in some circumstances to conform to the space constraints of some electrical panels.

The expansion module 30 may include a module

interface 40 (as illustrated in Figures 3a) that

facilitates communication with auxiliary systems (such as diagnostics tools) . An exploded view of the module

interface 40 is depicted in Figure 3b. The illustrated module interface 40 comprises a RJ45 port 44, screw terminals 43, a USB port 42 and SMA connector 41. The base unit 10 may incorporate communications circuitry to facilitate data exchanges via a

communications network. Figure 6 illustrates several utility meters 1 interconnected by a communications network. The illustrated utility meters 1 have a wireless communications interface that facilitates the exchange of data with other devices connected to the network.

The data network depicted in Figure 6 is a radio mesh network 69. The radio mesh network 69 facilitates the exchange of data between the illustrated utility meters 1. A gateway device 68 exchanges data between the radio mesh network 69 and an external data network, such as the internet 65.

A head end system 67 communicates with the utility meters 1 via the gateway device 68. The head end system 67 collects data from the utility meters 1. It may also configure and/or regulate operation of devices (such as the utility meters 1 or gateway device 68) within the radio mesh network 69. The head end system 67 communicates with device connected to the radio mesh network 67 via an auxiliary data network 65 (such as the internet) through the gateway device 68.

The communications circuitry (usually a wireless communications module) is optionally integrated with a printed circuit board (PCB) within the base unit 10.

Typical wireless communications circuitry incorporates an integrated circuit transceiver, oscillator, filter and several passive components (inductors, capacitors,

resistors) . The transceiver is usually connected to a base unit controller (such as a microcontroller or similar processing unit) via a standard system bus (such as an SPI bus and/or UART) . The communications circuitry may be controlled by the base unit controller or an independent communications control system.

The communication circuitry may be integrated with a master printed circuit board (PCB) within the base unit 10 or contained on a slave printed circuit board (PCB) that connects to the master board. Communications firmware updates may generally managed via the base unit

controller .

The communications circuitry illustrated in Figure 6 operates on radio networks (such as the unlicensed 900MHz Australian ISM network. This network supports industrial, scientific and medical devices in the 915MHz-928MHz frequency band. Output power is limited to approximately 25mW on this band. Operation on different bands and at different output power ratings is possible. This is achieved by using alternate filtering and passive

components (usually within the same electronics

footprint) . A radio amplifier may be used to increase output power. Optical communications (via optic fibre) and communications via the distribution network are also possible . Wireless communications circuitry may be compliant with IEEE standard 802.15.4g (Low-Rate Wireless Personal Area Networks) . The upper layers of the communications stack defined by IEEE standard 802.15.4g are executed by in firmware (either within a base unit controller or dedicated communications controller) . This enables the utility meters 1 to exchange data packets with other 802.15.4g complaint devices.

The communications circuitry may implement alternate standards, such as discarding upper layers of the

communications stack (typically limiting usage to the application layer) or use a proprietary wireless mesh network in place the IEEE standard 802.15.4g protocol. This includes communication via a cellular (mobile phone) transceiver module contained with the base unit. The utility meters 1 depicted in Figure 6 exchange data with a head end system 67. The is facilitated by wireless communications circuitry within the base unit 10 of each illustrated utility meter 1. Several

communications routes may be used to link the meters 1 and head end system 67. The illustrated meters 1 connect to a gateway device 68. This connection may be direct (i.e. meter 1 to gateway device 68) or via other devices. For example, an individual meter 1 may link through other local meter to access the gateway device 68 (such as a master meter 1 installed on each floor of a high density residential installation) .

The head end system 67 manages a population of utility meters 1. The head end system 67 typically stores asynchronously received meter data, backups meter data, generates billing information, issues commands to

individual meters and tests for faults. It may also manage the communications network used to exchange data with the utility meters 1.

It will be understood to persons skilled in the of the invention that many modifications may be made without departing from the spirit and scope of the

invention .

It is to be understood that, if any prior art

publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

1. An electrical utility meter base unit comprising:

a housing having a rear face arrange to mount to a support structure and an opposing front face with a display unit,

a mains interface arrange to connect the utility meter to a distribution network, the mains interface comprising a plurality of input terminals mounted to the base unit and electrically connected to the metrology circuitry,

a site interface arrange to connect the utility meter to a local site network, the site interface comprising a plurality of output terminals mounted to the base unit and electrically connected to the metrology circuitry,

an expansion interface arrange to connect an

a mounting interface accessible via the front face of the housing arrange to support an expansion module, the mounting interface defining a mounting footprint for expansion modules that is bounded at an upper limit by the display unit, the mounting footprint being unbound forward of the housing.

2. The base unit of claim 1 wherein the electrical

coupling and the data interface of the expansion interface are spatially separated to reduce electrical interference.

3. The base unit of claim 2 wherein the electrical

coupling and the data interface of the expansion interface are spatially separated by more than 5cm.

4. The base unit of any one of claims 1 to 3 wherein the mains interface and the data interface are spatially separated to reduce electrical interference, thermal interference and magnetic interference.

5. The base unit of claim 4 wherein the mains interface and the data interface are spatially separated by more than 8cm.

6. The base unit of any one of claims 1 to 5 comprising an extra-low voltage plate disposed between the mains

interface and the expansion interface.

7. The base unit of any one of claims 1 to 6 comprising communications circuitry arrange to exchange data with communications networks external to the utility meter, the communications circuitry being mounted within the housing.

8. The base unit of any one of claims 1 to 7 comprising a high current switch that is electronically controlled by circuitry within the base unit to electrically connect the mains interface with the site interface.

9. An electrical utility meter system comprising the base unit of any one of claims 1 to 8, and

a plurality of expansion modules that are configured to connect electrically to the base unit via the expansion interface, each of the expansion modules having a mating surface that seats adjacent the front face of the base unit and an opposing front panel that projects forward of the base unit housing, the expansion modules having dissimilar volume, defined by the distance between the mating surface and front panel.

10. A utility meter system comprising:

a base unit comprising a housing having a rear face arrange to mount to a support structure and an opposing front face, metrology circuitry enclosed within the housing arrange to monitor energy exchanged between a consumer site and an electrical distribution network, and an expansion interface arrange to connect an expansion module to circuitry within the base unit, the expansion interface having an electrical coupling arrange to

provides a low impedance connection to an electrical distribution network, and

11. The system of claim 10 wherein the base unit has a mounting interface accessible via the front face of the housing arrange to support an expansion module, the mounting interface defining a mounting footprint for expansion modules that is bounded at an upper limit by a display unit mounted within the housing adjacent the front face .

12. The system of claim 10 or claim 1 comprising a mains interface arrange to connect the utility meter to a distribution network, the mains interface comprising a plurality of input terminals mounted to the base unit and electrically connected to the metrology circuitry, and

13. The system of claim 12 wherein the expansion interface comprises an electrical coupling arrange to provide a low impedance connection to an electrical distribution network to a mounted expansion module and a separate data

interface arrange to transfer digital data between the base unit and a mounted expansion module.

14. The system of claim 13 wherein the electrical coupling and the data interface of the expansion interface are spatially separated to reduce electrical interference.

15. The system of claim 14 wherein the electrical coupling and the data interface of the expansion interface are spatially separated by more than 10cm.

16. The system of any one of claims 12 to 15 wherein the mains interface and the expansion interface are spatially separated to reduce electrical interference.

17. The system of claim 16 wherein the electrical mains interface and the expansion interface are spatially separated by more than 15cm.

18. The system of any one of claims 12 to 17 comprising an extra-low voltage plate disposed between the mains

interface and the expansion interface.

19. The system of any one of claims 10 to 18 comprising a high current switch that is electronically controlled by circuitry within the base unit to electrically connect the mains interface with the site interface.

20. The system of any one of claims 10 to 19 comprising communications circuitry that exchanges data with

communications networks external to the utility meter, the communications circuitry being mounted within the base unit housing.

21. A plurality of expansion modules that are configured to connect electrically to an electrical utility meter base unit via an expansion interface, each of the

expansion modules having a mating surface that seats adjacent a front face of the base unit and an opposing front panel that projects forward of the base unit housing when mounted,

22. An electrical utility meter base unit comprising:

a housing,

an expansion interface arrange to connect an

interference.

23. An electrical utility meter base unit comprising:

an expansion interface arrange to connect an

24. An electrical utility meter base unit comprising:

a housing,

an expansion interface arrange to connect an

communications circuitry arrange to exchange data with communications networks external to the utility meter, the communications circuitry being mounted within the base unit housing.