GB2375664A

GB2375664A - Electrical power distribution bus

Info

Publication number: GB2375664A
Application number: GB0112291A
Authority: GB
Inventors: Robert Leigh
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-05-19
Filing date: 2001-05-19
Publication date: 2002-11-20
Also published as: GB0112291D0

Abstract

An electrical power distribution 10 (Figure 2) comprises a plurality of spurs 20 for supplying power to equipment 17, 19 connected individually to the spurs, conveniently as a trailing block of outlet sockets (50, Figure 3) with which equipment plug connections are made. At least one spur 20<SB>G</SB> forms a controlling spur and current drawn by connected equipment 17 is sensed at 30 and compared with a threshold in comparison and control means 40 which responds to the drawn current falling below a predetermined value to individual supply of power to the other, controlled spurs 20<SB>D</SB>, 20<SB>D2</SB> etc and thus equipment 19. This enables subsidiary equipment, eg computer peripherals, to be powered-up and powered-down in accordance with controlling the power drawn by master equipment eg. a computer. The comparison and control means may respond to drawn current exceeding a threshold to inhibit supply to the controlled spurs to prevent an overload situation.

Description

Electrical Power Distribution Bus This invention relates to electrical power distribution buses and particularly, but not exclusively, to such buses for domestic and office use.

It is common in domestic and office premises to employ a large number of pieces of portable and/or self-contained electrical equipment, each of which pieces is individually powered by way of a discrete plug and socket connection with a power distribution bus. The primary source of electrical power in such premises is usually by way of a distribution bus forming a ring main extending around the premises with outlet sockets distributed therealong at intervals. Such outlet sockets are constrained by the routing of the ring main and are often confined to wall mounting locations whereas it may be required to operate equipment displaced from such wall mounted locations.

To facilitate the use of portable equipment or dispose equipment other than adjacent such ring main it is known to provide as a spur to the ring main a distribution bus, which is fed from one end by the ring main as a source, and including one or more outlet spurs each terminating in an outlet socket or clamping terminal for individual connection of discrete pieces of equipment.

This specification is concerned solely with such distribution bus that forms a spur from a source and herein the term"distribution bus"is used in that context, and notwithstanding that the bus itself feeds one or more outlet spurs, which for convenience are referred to herein simply as "spurs".

Such a distribution bus may be mounted for use in relatively fixed position, for example, to a piece of furniture, or may comprise a free-standing housing that forms a block of outlet sockets and arranged to be connected by a flexible cable to a ring main socket, permitting the block to

be positioned and/or moved as desired and said multiple pieces of equipment, each with a power supply cable, to be connected to the source by way of said single cable. Such free-standing distribution bus blocks which are connected to the source by, and trail from, a flexible connecting cable are also known as trailing blocks.

Whereas such trailing or mounted distribution blocks are convenient in removing some constraints on where pieces of equipment can conveniently be used, aesthetic considerations and their use by unskilled persons often limit the ability to obtain maximum benefits from them.

For example, such a block is frequently mounted so as to be unseen and as a consequence is often unreachable when in use and equipment connected, to the extent that having to operate on the block from necessity is inconvenient or difficult, and operating on it at any other time is likely to be avoided. It is known to provide the various outlet sockets with switches whereby each individual piece of equipment can be isolated from the block, and to provide a master switch for isolating all outlet sockets by a single operation. However, as access is required for switch operation, in many instances such facility may be unused, and for this reason many such trailing block distribution buses included the minimum of features.

Also, such distribution blocks are provided with a plurality of sockets but insofar as the distribution bus of a block itself is a spur circuit, there is a limit to the total current which can be safely drawn from the distribution bus as a whole. Such distribution blocks sometimes contain a fuse or resettable circuit breaking device which responds to the total current drawn by the connected pieces of equipment, and whereas this does not preclude the use of, say, a single piece of high-current equipment such as a heater provided other equipment is disconnected or switched off, difficulty of access for replacement or resetting such circuit breaking device, should current limits be exceeded, in addition to accessing any equipment controllable only from the block that may be necessary to avoid said excess, may effectively limit the practicability of

operating selected pieces of equipment which draw sufficiently high current to risk additional equipment causing the limit of the bus to be exceeded, even if the use of such high current equipment is a decision which is within the capability or concern of a user.

Although such high current use places constraints on such end-fed, distribution buses which may, in combination with accessibility, limit their full potential, by far the greatest uses are in relation to what may be termed low-current devices, such as personal computers and their peripheral devices equipment and audio-visual equipment. Such equipment forms are of particular interest in that although each form may comprise a plurality of separately powered devices, there is often a central or master device to which the other devices are peripheral, or subsidiary to it and have limited functionality without the master device. For example a personal computer system may include not only a central processing unit, but also a separately powered VDU, printer, scanner, modem and audio equipment. Because such peripheral devices are often quiet when powered but not functioning, and computers may automatically power-down by software therein, the user may neglect and/or find it inconvenient to remove power from all of the peripheral devices individually, but equally difficult or impracticable to remove power to such devices together by way of the distribution block if it is located inconveniently and out of reach.

Notwithstanding that such a distribution block is, as a spur circuit, only one form of a distribution bus which may take a variety of fixed and movable forms in providing power to one or more outlet spurs, it is an object of the present invention to provide an electrical power distribution bus of simple form that has the ability to control the connection of power to discrete pieces of external equipment without operational access to the distribution bus. It is also an object of the present invention to provide a method of controlling the connection of powerto discrete pieces of external equipment connected to a distribution bus without access to the distribution bus.

According to a first aspect of the present invention an electrical power distribution bus comprises

a plurality of spurs connected thereto for supplying power to equipment connected individually to said spurs, current sensing means associated with at least one, controlling spur operable to determine the level of controlling spur current drawn by equipment connected thereto, and comparison and control means, associated with each said controlling spur and at least one other, controlled spur of the bus, responsive to the level of the or each determined controlling spur current in relation to at least one threshold level to control the supply of power to each said associated controlled spur of the bus.

The comparison and control means may include threshold setting means operable to effect setting of the or each comparison threshold level. Such threshold setting means may comprise a potentiometer, or memory means and programming means operable to set therein one or more values defining a threshold. The threshold setting means may be arranged to be set manually and/or be set remotely, in which case the setting means may be arranged to be set by signals received along the bus.

The current sensing means associated with each controlling spur may be operable to develop a current-related voltage across a load impedance connected in series with a said controlling spur, and the comparison and control means may have threshold setting means operable to provide a switching voltage threshold and be operable to compare said current-related voltage with the switching voltage threshold, being responsive to existence of a predetermined relationship between them to effect switched connection of each associated controlled spur with the bus.

The power distribution bus is adapted to be coupled at one end thereof to a power source and preferably includes a plurality of controlled spurs separated from said one end by at least one controlling spur, the comparison and control means being arranged to couple said supply to each said associated controlled spur by way of connecting or interrupting the bus between the

controlling and controlled spurs, conveniently, but not necessarily, by switching means disposed to interrupt the bus between the controlling and controlled spurs.

In one implementation, each controlled spur may terminate in a socket adapted to receive a plug of said discrete equipment, as may each controlling spur. The bus and said sockets may be housed and comprise a trailing distribution block.

The comparison and control means associated with any controlled spur may by responsive to controlling spur current exceeding a threshold level set therein to interrupt supply of power to each said associated controlled spur. Additionally or alternatively, the comparison and control means associated with any controlled spur may be responsive to determined current in any associated controlling spur falling below a threshold level set therein to interrupt supply of power to each said associated controlled spur. Alternatively, the comparison and control means associated with any controlled spur may be responsive to determined current in each associated controlling spur falling below a threshold level set therein to interrupt supply of power to each said associated controlled spur.

The electrical power distribution bus defined in the above paragraphs and comprising a plurality of controlled spurs may have at least one said controlled spur forming a sub-set thereof, comparison and control means associated with said sub-set being responsive to the level of a determined current of a controlling spur relative to a threshold level therefor to control the supply of power to said associated sub-set.

The electrical power distribution bus of the preceding paragraph may include at least first and second controlling spurs, each having associated current sensing means, said comparison and control means associated with a sub-set of controlled spurs being responsive to the level of a determined current of one of said controlling spurs relative to a threshold level therefor to

control the supply of power to said associated sub-set of controlled spurs. Furthermore, said one controlling spur may be a controlled spur of another controlling spur.

Electrical power distribution bus as defined above may include at least first and second controlling spurs, each having associated current sensing means, and wherein detected controlling spur current of one spur provides the threshold level for the other spur.

According to a second aspect of the present invention a method of electrical power distribution by a distribution bus, having a plurality of spurs connected thereto for supplying power to equipment connected individually to said spurs, comprises determining the level of current drawn by equipment connected to at least one, controlling spur and comparing it with a threshold level, and as a result of such comparison enabling or preventing the supply of power to at least one other, controlled spur of the bus.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which : Figure 1 is a schematic circuit block diagram of a first embodiment of electrical power distribution bus in accordance with the present invention, having a single controlling spur and a plurality of controlled spurs, Figure 2 is a circuit diagram illustrating in detail current sensing means and comparison and control means of Figure 1, Figure 3 is a schematic representation of a trailing block of multiple socket outlets incorporating electrical power distribution bus of Figure 1,

Figure 4 is a schematic circuit block diagram of a second embodiment of electrical power distribution bus in accordance with the present invention, illustrating the use of two controlling spurs each associated separately with a plurality of controlled spurs, Figure 5 is a schematic circuit block diagram of a third embodiment of electrical power distribution bus illustrating the use of two controlling spurs, but in which plurality of controlled spur associated with one controlling spur form a sub-set of spurs controlled by the other controlling spur, Figure 6 is a schematic circuit block diagram of a fourth embodiment of electrical power distribution bus illustrating a controlled spur forming a controlling spur for a sub-set of controlled spurs, Figure 7 is a schematic circuit block diagram of a fifth embodiment of electrical power distribution bus illustrating controlling of the controlled spurs and sub-set of controlled spurs by different current levels in a single controlling spur, and Figure 8 is a schematic circuit block diagram of a sixth embodiment of electrical power distribution bus illustrating two controlling spurs in which current flow in one provides the threshold against which current flow in the other is compared by comparison and control means.

Referring to Figure 1 an electrical power distribution bus 10 comprises a live rail 12 and neutral or return rail 14, and optionally a ground or earth rail shown ghosted at 15. The bus is end fed, that is, the rails are arranged for operation to be connected at an end 10'to a source 16 of electrical power such as a ring main or generator. The bus is effectively a spur of a source circuit and the other end 10"is not separately connected to such source.

To provide operating power to discrete, and possibly remote, items of equipment, shown ghosted

at 17 and 19, the bus comprises a plurality of individual spurs indicated generally at 20, each having connections to the respective live and neutral rails.

In accordance with the present invention spur 20G adjacent the feed end 10'comprises a controlling spur whereas those further away from the end 10'comprise controlled spurs 20D1' 20D2, 20D3....

The controlling spur 20G has associated therewith current sensing means 30 which is operative to determine the level of controlling spur current drawn by equipment (17) connected thereto, and associated with the controlled spurs is comparison and control means 40 which is responsive to the level of the determined controlling spur circuit, in relation to a threshold level, to control the supply of power to each controlled spur and equipment (19) connected thereto. The comparison and control means 40 includes threshold setting means 42 operable to effect setting of the comparison threshold level, either fixed during manufacture or variable by a user, comparator means 44 to effect comparison between signals representative of the set threshold and determined current levels and control means to effect switching that either connects the controlled spurs to, or disconnects them from, the feed end 10'by completing or interrupting the rail 12.

In one form of the embodiment, the comparison and control means 40 is arranged to respond to a determined controlling spur current being less than a predetermined threshold level to interrupt power supply to the controlled spurs.

In this way, if equipment 17 connected to the controlling spur is operated remotely of the distribution bus 10 such that the level of current drawn thereby is above the threshold level, then the controlled spurs 20D1, 20D2... are empowered to permit items of equipment connected thereto also to draw current; if the equipment 17 is operated to reduce the current drawn thereby to

below the threshold level, such as being turned off or into a stand-by mode, then power is removed from all of the equipment items connected to the controlled spurs. If the equipment 17 subsequently causes an increase in the level of current drawn from the spur 20G above the threshold level, then the comparison and control means automatically restores power to the controlled spurs.

Thus, the remote equipment 17 is able to control the supply of power to other equipment 19, as a master-slave relationship, on the basis of current drawn by that equipment.

It will be appreciated that in the distribution bus 10, in addition to a controlling spur 20G and controlled spurs 20D1'2002...., there may also be provided one or more uncontrolled spurs, shown ghosted at 20U.

Referring now to Figure 2, this shows in greater detail the controlling spur current sensing means 30 and the comparison and control means 40.

The current sensing means 30 comprises, in series with the controlling spur, a load impedance 32 across which a voltage is developed related to the current drain by connected equipment 17. The voltage is rectified and smoothed conventionally by components 34 and provided as a controlling spur load signal to node 36. Within the comparison and control means 40, the aforementioned threshold setting means 42 comprises a potentiometer 43 which is connected at its ends 431 and 432 to the node 36 and neutral rail 14 respectively. The potentiometer includes a tap 433 which is connected to the base terminal of a switching transistor 47 connected between the rails 12 and 14 in series with an operating coil of switching means in the form of relay 48. The relay 48 includes at least one switch 49 that in series with the bus rail 12 is connected to associated controlled spurs 2001, 20...... The section of bus rail to which the controlled spurs are all connected is denoted as 12D, that is, single switch 49 controls current flow

to all of the controlled spurs 2001. 2002.....

The emitter terminal of the switching transistor is connected to the neutral rail 14 and insofar as the threshold setting means 30 is arranged to derive at the potentiometer tap 433 a proportion of the controlling current-related voltage at node 36, when the controlling current is such that the set proportion of its related voltage exceeds the forward bias threshold of the transistor, the transistor conducts and switching relay 48 connects spurs 20D1, 20D2... to the feed end 10'of the bus.

If and when the level of current drain by equipment in the controlling spur produces such currentrelated voltage at node 36 that the tapped proportion at 433 is insufficient to forward bias the transistor 47, the transistor ceases to conduct, the relay 48 is de-energised and the controlled spurs 20du, 2002... connected to rail portion 12D are decoupled from the source of power.

It will be appreciated that the potentiometer 43 may be fixed during manufacture to provide a suitable forward bias voltage in response to a predetermined controlling spur current. Such current may be set relatively low, say tenths of an amp to permit the normal operating current of most electrical and electronic equipment to enable the controlled spurs but absence of such current to disable the controlled spurs. For better control the potentiometer 43 may be made adjustable, possibly by the user, to set a desired threshold that may be related to particular equipment (17) with which used, or even particular operating modes of such equipment.

For example, the setting means may be adjusted to provide a threshold that distinguishes change of current drawn by controlling spur equipment between normal operation and a lower, stand-by level or between a low stand-by level and totally off.

Although a manually adjustable potentiometer provides convenient and cost effective threshold

setting means, it may be difficult to set accurately if the threshold is critical and require access to the distribution bus for normal adjustment. It will be appreciated that such potentiometer may be replaced by circuitry, possibly digital, that includes memory means into which can be set by programming means one or more threshold values for subsequent selection and comparison with a determined controlling spur current, or load signal, or representation thereof, either in the digital or analogue domain. Insofar as threshold setting levels are input manually they may be keyed into circuitry situated at the bus, but alternatively, if setting level information may be superimposed upon the low frequency power of the bus, they may be applied remotely.

Employment of memory and programming means may permit the possibility of effecting threshold setting by a'leaming'process that depends upon different current levels associated with equipment connected to the controlling spur. For example, the memory means may be exposed to a controlling-spur current (or a related voltage) that represents a desired state permitting power to the controlled spurs and then exposed to a controlling-spur current that represents a state permitting power to the controlled spurs and then exposed to a controlling-spur current that represents a state preventing power to the controlled spurs. The threshold setting means may make available both learned values of the comparison and control means or derive an intermediate value as the effective threshold value for comparison.

It will also be appreciated that alternatives may be provided for other functional components of the comparison and control means and for the current sensing means, both in dependance upon whether or not the threshold setting means is primarily digital or analogue in nature and independently thereof. The switching means 48 may be provided by a solid state, semiconductor device instead of a relay with physically operable contacts and/or may control the various controlled spurs individually. The comparison and control means may be provided by other than a transistor and the use of voltage associated with forward biasing thereof, such as a gating circuit of electrical or optical signals. Also, it may be possible to effect comparison between the

controlling spur current and a threshold current level directly without first deriving a current- related voltage.

However, the current sensing and comparison and control means of Figure 2 is able to offer simplicity and low cost of implementation in a distribution bus of the aforementioned domestic distribution block type in which the spurs terminate in equipment connection sockets.

Referring to Figure 3, this shows the schematic arrangement of Figure 1 in which the distribution bus 10 is incorporated in a distribution block 50 whose physical dimensions are defined by a plurality of outlet sockets indicated generally at 52 for connection of external equipment. The block includes the above described live neutral and ground rails 12,14 and 15 which extend from a end 50'of the block as a flexible cable 54 to a plug 56 which may be plugged into a ring main or like source.

The sockets 52 have corresponding terminals thereof connected to the rails 12,14 and 15 and comprise the spurs of the distribution bus. To extend the comparison with Figure 1, the socket 52u terminates an uncontrolled spur 20u'socket 52G terminates the controlling spur 20G and sockets 52DI, 52D2 terminate controlled spurs 20D1, 20D... Enclosed within the distribution block is the controlling spur current sensing means 30 and the comparison and control means 40, the latter including threshed setting potentiometer 43 or an alternative, optionally accessible for manual adjustment, and switching means 48 in the live rail separating the controlling and controlled spurs. It will be appreciated that the current sensing means and the comparison and control means may be implemented compactly and utilise space available in a conventional distribution block of this type.

Insofar as one socket comprises the controlling spur and others the controlled spurs, there may be provided external markings or colour coding to alert the user to the different functions.

It will be appreciated that although the above description has concentrated upon determining when controlling spur current falls below a threshold level to remove power from controlled spurs, it may be arranged to have such effect alternatively or additionally when the controlling current exceeds a threshold level.

Such an arrangement may be used where equipment connected to the controlling spur is able to draw current approaching the safe limit of the distribution bus, and in such event other equipment, connected to the controlled spurs, has power removed that prevents a total current drawn through the bus being sufficient to trip a circuit breaking device and disable the distribution spur until manually replaced or reset, power being restored thereto automatically when current drain by the controlling spur falls to an acceptable level.

It will be appreciated that comparison and control means may be arranged to respond to a plurality of thresholds to effect decoupling of power from controlled spurs, that is, enable power supply thereto only whilst the current drain from the controlling spur is between higher and lower threshold limits. Such arrangement may be employed to provide power to peripheral equipment connected to the controlled spurs whilst controlling equipment is operating normally but to remove such power when the equipment is powered down to an'off'or'stand-by'condition, or if it draws excessive current.

It will be appreciated that a distribution bus as described above, and with the optional and alternative features thereof, may be further varied without departing from the invention.

Referring means to Figure 4 this shows a schematic representation of a second embodiment of distribution bus 102 which is of similar form to the distribution bus 10 and corresponding parts are given like reference numbers. It differs from distribution bus 10 in that there are two controlling spurs 20G1 and 20G2 each of which has current sensing means 301 and 302 respectively. Each

current sensing means is associated with comparison and control means 401 and 402 respectively and in turn, associated with each is a plurality of controlled spurs 20D11: 20D12,... and 20D21' 20D22' ... respectively.

In operation each controlling spur may separately control the provision of power to controlled spurs associated with it in dependence on a uniquely set threshold level (controlling spur current) and independently of the threshold conditions attaching to the other controlling spur. For example one controlling spur may remove power to its associated controlled spurs when the current drawn exceeds a threshold value therefor whilst the other removes power if the controlling spur current is less than an associated threshold value, or both may respond to the respective controlling spur currents exceeding, or being less than, respective thresholds.

Referring to Figure 5, this shows a schematic representation of a third embodiment of distribution bus 103 in which like bus 103 there are two controlling spurs 20G1 and 20G2 but wherein the controlled spurs 20021'20022.... associated with controlling spur 20G2 are a sub set of the controlled spurs associated with 20G1, the comparison and control means 402 being in controlled spur 20011 in parallel with other controlled spurs 20012. 20013.... Thus, the controlling spur 20 represents a master controlling spur which overrides control effected by controlling spur 20G2.

Referring to Figure 6, this shows a schematic representation of a fourth embodiment of distribution bus 104 in which there are also two controlling spurs 20G1 and 20G2, the latter being a controlled spur equating to controlled spur 20011 of spurs 20011. 20D12, 20D13... of controlling spur 20G1'The comparison and control means 402 of controlling spur 20G2 has associated therewith controlled spurs 20D21, 20D22, ... which form a subset of the spurs controlled by the spur 20G1 which effects an overall or master control.

Referring to Figure 7, this shows a schematic representation of a fifth embodiment of distribution

bus 105 which is somewhat similar to the distribution bus 103 of Figure 5 that it includes a spur controlled by comparison and control means 401, (effectively controlled spur 20011), second comparison and control means 402 associated with a sub-set of controlled spurs 20D21, 2ou2...... but differs in that it contains only a single controlling spur 20G1 having sensing means 301 that determines controlling spur current for both the comparison and control means 40, and 402 One, say 402, may respond to controlling current falling below an upper threshold to remove power from the controlled spurs of the sub-set whilst the other, 401, may respond to controlling current falling below a lower threshold level to remove power from all of the controlled spurs.

Alternatively, the comparison and control means 401 may respond to controlling current exceeding an upper threshold level to remove power from all of the controlled spurs, including those of the sub-set.

In all of the above described embodiments the control and comparison means has been described as making comparison of one or more controlling spur currents (or current related signals) with an absolute level chosen in advance.

Referring now to Figure 8, this shows a schematic representation of a sixth embodiment of distribution means 106 which is generally similar to the embodiment 10 in having a plurality of controlled spurs 20D1, 2002'.... but differs in having two controlling spurs 20G, and 20G2 each of which has individually associated current sensing means 301 and 302 which both provide controlling current related signals to comparison and controlling means 403, the latter being arranged to effect comparison on the basis of their relative levels, that is, the controlling current level of one spur provides the threshold level for the other.

It will be appreciated that various other configurations may be derived by combination of, or simple extension of the arrangements used in above described embodiments, such as the number of controlling spurs, the number of controlled spurs and comparison and control means

associated with each controlling spur and the number of subsidiary controlled sub-set spurs, but in all cases provides the possibility of compact and cost effective incorporation in a variety of distribution bus arrangements.

Whilst it is the intention of the present in invention to be suitable for incorporation into electrical distribution spurs for domestic and office use, which in practice usually have a plurality of socket terminations, it should be noted that it is not limited by the number of controlling or controlled spurs nor to use with such distribution spurs having socket terminations and may be adapted for use with more permanent, fixed or clamping terminations.

Claims

Claims 1. Electrical power distribution bus comprising a plurality of spurs connected thereto for supplying power to equipment connected individually to said spurs, current sensing means associated with at least one, controlling spur operable to determine the level of controlling spur current drawn by equipment connected thereto, and comparison and control means, associated with each said controlling spur and at least one other, controlled spur of the bus, responsive to the level of the or each determined controlling spur current in relation to at least one threshold level to control the supply of power to each said associated controlled spur of the bus.
2. Electrical power distribution bus as claimed in claim 1 in which the comparison and control means includes threshold setting means operable to effect setting of the or each comparison threshold level.
3. Electrical power distribution bus as claimed in claim 2 in which the threshold setting means is arranged to be set manually.
4. Electrical power distribution bus as claimed in claim 2 or claim 3 in which the threshold setting means is arranged to be set remotely.
5. Electrical power distribution bus as claimed in any one of claims 2 to 4 in which the threshold setting means comprises memory means and programming means operable to set therein one or more values defining a threshold.
6. Electrical power distribution bus as claimed in claim 5 when dependant on claim 4 in

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which the setting means is arranged to be set by signals received along the bus.
7. Electrical power distribution bus as claimed in clam 3 in which the threshold setting means comprises a potentiometer.
8. Electrical power distribution bus as claimed in any one of claims 2 to 7 in which the current sensing means associated with each controlling spur is operable to develop a current-related voltage across a load impedance connected in series with a said controlling spur, the comparison and control means has threshold setting means operable to provide a switching voltage threshold, and is operable to compare said current-related voltage with the switching voltage threshold and responsive to existence of a predetermined relationship between them to effect switched connection of each associated controlled spur with the bus.
9. Electrical power distribution bus as claimed in any one of the preceding claims in which the power distribution bus is adapted to be coupled at one end thereof to a power source and includes a plurality of controlled spurs separated from said one end by at least one controlling spur, the comparison and control means being arranged to couple said supply to each said associated controlled spur by way of connecting or interrupting the bus between the controlling and controlled spurs.
10. Electrical power distribution bus as claimed in claim 9 in which the comparison and control means includes switching means disposed to interrupt the bus between the controlling and controlled spurs.
11. Electrical power distribution bus as claimed in any one of the preceding claims in which each controlled spur terminates in a socket adapted to receive a plug of said discrete

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equipment.
12. Electrical power distribution bus as claimed in any one of the preceding claims in which each controlling spur terminates in a socket adapted to receive a plug of said discrete equipment.
13. Electrical power distribution bus as claimed in claim 11 or claim 12 in which the bus and said sockets are housed and comprise a trailing distribution block.
14. Electrical power distribution bus as claimed in any one of the preceding claims in which the comparison and control means associated with any controlled spur is responsive to controlling spur current exceeding a threshold level set therein to interrupt supply of power to each said associated controlled spur.
15. Electrical power distribution bus as claimed in any one of the preceding claims in which the comparison and control means associated with any controlled spur is responsive to determined current in any associated controlling spur falling below a threshold level set therein to interrupt supply of power to each said associated controlled spur.
16. Electrical power distribution bus as claimed in any one claims 1 to 14 in which the comparison and control means associated with any controlled spur is responsive to determined current in each associated controlling spur falling below a threshold level set therein to interrupt supply of power to each said associated controlled spur.
17. Electrical power distribution bus as claimed in any one of claims 1 to 13 comprising a plurality of controlled spurs having at least one said controlled spur forming a sub-set thereof comparison and control means associated with said sub-set being responsive

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to the level of a determined current of a controlling spur relative to a threshold level therefor to control the supply of power to said associated sub-set.
18. Electrical power distribution bus as claimed in claim 17 including at least first and second controlling spurs, each having associated current sensing means, said comparison and control means associated with a sub-set of controlled spurs being responsive to the level of a determined current of one of said controlling spurs relative to a threshold level therefor to control the supply of power to said associated sub-set of controlled spurs.
19. Electrical power distribution bus as claimed in claim 18 in which said one controlling spur is a controlled spur of another controlling spur.
20. Electrical power distribution bus as claimed in any one of claims 1 to 16 including at least first and second controlling spurs, each having associated current sensing means, detected controlling spur current of one spur providing the threshold level for the other spur.
21. Electrical power distribution bus comprising a plurality of spurs connected thereto for supplying power to equipment connected individually thereto, substantially as herein described with reference to, and as shown in, Figures 1 to 4 or any one of Figures 5 to 8 of the accompanying drawings.
22. A method of electrical power distribution by a distribution bus having a plurality of spurs connected thereto for supplying power to equipment connected individually to said spurs, the method comprising determining the level of current drawn by equipment connected to at least one, controlling spur and comparing it with a threshold level, and

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as a result of such comparison enabling or preventing the supply of power to at least one other, controlled spur of the bus.
23. A method as claimed in claim 22 comprising defining at least one controlled spur as a sub-set of a plurality of controlled spurs and employing at least one of said controlled spurs out of the sub-set as a controlling spur of the sub-set.
24. A method as claimed in claim 22 or claim 23 comprising comparing the level of current drawn by equipment connected to said at least one controlling spur with upper and lower threshold levels and in response to such level being between said threshold levels enabling the supply of power to at least one controlled spur of the bus.
25. A method as claimed in any one of claims 22 to 24 comprising comparing the level of current drawn by equipment connected to a plurality of controlling spurs with different threshold levels.
26. A method as claimed in any one of claims 22 to 25 comprising comparing the level of current drawn by equipment connected to a controlling spur with a threshold determined by the level of current drawn by equipment connected to a different controlling spur.
27. A method of electrical power distribution by a distribution bus having a plurality of spurs connected thereto for supplying power to equipment connected individually to said spurs, the method being substantially as herein described with reference to the accompanying drawings.