BACKGROUND In a power distribution network air break switches or other circuit breakers are typically mounted at or near the pole-top and include an actuation mechanism such as a lever in a simplest form, operable from closer to ground level by a linesman or maintenance worker to actuate the air break switch. The actuation lever is connected by a shaft or similar up the pole to the mechanical air break switch at the pole top. The air break switch may be operated by the linesman or maintenance worker to open to break the circuit or line, and to close the air break switch to reconnect power after maintenance or fault finding has been finished.

SUMMARY OF INVENTION The invention provides an electric motor and gear box drive assembly which is operable to provide output drive from the gear box either by operation of the electric motor or manually. The invention also provides an actuator for a circuit breaker such as a pole-top or near pole-top air break switch, which enables the circuit breaker to be actuated either electrically, by a control signal over a radio link to a radio receiver and controller associated with the actuator, or manually by a linesman or maintenance worker at the pole.

In broad terms in one aspect the invention comprises an electric motor and gear box drive assembly which is operable to provide output drive from the gear box either by operation of the electric motor or manually, including an electric motor and a gear box movably mounted relative to one another such that the motor drive is in one

relative position between the motor and the gear box connected through the gear box to an output drive from the gear box, and is in another relative position between the motor and the gear box disconnected through the gear box, and a manual drive shaft to the gear box which can be manually rotated to provide output drive from the gear box at least when the motor is disconnected from the output shaft from the gear box.

In broad terms in another aspect the invention comprises an actuator for a circuit breaker at or near a pole top, including an electric motor and gear box drive assembly which is operable to provide output drive from the gear box to a circuit breaker either by operation of the electric motor or manually, including an electric motor and a step-down gear box movably mounted relative to one another such that the motor drive is in one relative position between the motor and the gear box connected through the gear box to an output drive from the gear box, and is in another relative position between the motor and the gear box disconnected through the gear box, and a manual drive shaft to the gear box which can be manually rotated to provide output drive from the gear box at least when the motor is disconnected from the output shaft from the gear box, without back driving the electric motor.

Preferably the actuator includes a lever mechanism associated with the electric motor and gear box and which is operable to move the motor relative to the gear box.

Typically where the gear box and motor are part of an actuator for a circuit breaker, the gear box and motor will be mounted in a cabinet positioned near the base of the pole and the output drive shaft from the gear box will be connected via a shaft or other mechanical means extending up the pole to the circuit breaker. A radio receiver and motor control electronics may be housed within the cabinet along with optionally a battery power supply. The circuit breaker may be actuated via a remote radio signal. When the cabinet is opened by a linesman or maintenance worker at the pole, the motor drive may be disconnected and the circuit breaker actuated manually, via a crank handle or similar fitted to the manual drive shaft from the gear box, without back-driving the motor through the gear box.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described with reference to the accompanying drawings which show a preferred form of the invention, by way of example and without intending to be limiting. In the drawings: Figure 1 shows a preferred form of actuator for a circuit breaker such as a pole-top air break switch (not shown), Figure 2 schematically illustrates the operation of the two position lever for moving the motor to disconnect or reconnect the motor drive, and Figure 3 schematically shows the gear box and motor and the arrangement of gears within the gear box of the preferred form system.

DETAILED DESCRIPTION OF PREFERRED FORM The preferred form gear box and electric motor drive assembly are shown as part of an actuator for a pole top air break switch. A gear box 1 and motor 2 are mounted within a cabinet 3 which is fixed to a pole 4. The air break switch is mounted at or near the pole top (not shown) and drive from the actuator within the cabinet 3 to the pole top to open and close the air break switch is via shaft 6 to which the output shaft 7 of the gear box is connected. The motor 2 may be connected to the gear box 1 through a subsidiary step down gear box 10.

A radio receiver and motor controller board 8 (not shown in detail) are mounted within the cabinet 3, along with a battery 9. A radio signal may be sent from afar to energise the motor 2 and the motor drive is connected through the gear box 1 to the shaft 6 to operate the pole top air break switch to open or close the air break switch.

Alternatively the air break switch may be actuated manually by a linesman at the pole by unlocking and opening the cabinet door 5 and fitting a crank handle 11 to a manual drive shaft on the front face of the gear box 1, and rotating the crank handle to manually drive the shaft 6 and actuate the air break switch. Preferably when not in use the manual crank handle 11 is stored within the cabinet 3, for example is held

by spring clips or similar on the interior of the cabinet door 5 as shown in phantom outlined in Figure 1.

In Figure 3 the same reference numerals indicate the same components as in Figures 1 and 2. The motor drive is normally connected through output shaft 12 and bevel gear 13 to bevel gear 14 on the bottom of shaft 6. Gear 14 and gear 16 are connected via shaft 15 so that they rotate together. The manual drive shaft 17 into the gear box, to which the manual crank handle is fitted for manual actuation, is connected to gear 16 via gear 18. When motor 2 is energised and rotates output shaft 6, manual drive shaft 17 will also rotate (crank handle not attached). The motor 2 (and subsidiary gear box 10) are movable between two positions, as indicated by arrow A in Figure 3 and Figure 2. When the motor 2 is moved to the position indicated in broken lines gear 13 is disengaged from gear 14. The motor is moved to this position to disengage the motor from the gear box prior to manual actuation, so that when manual drive shaft 17 is rotated, the output shaft 6 will rotate but the motor will not be back-driven through the gear box. Typically subsidiary gear box 10 will provide a step down ratio of the order of 50: 1 so that it would not be possible or would be very difficult to otherwise manually operate the actuator with the motor connected.

Referring to Figure 2, in the preferred form gear box 1 is fixedly mounted within the cabinet 3. Lever 20 may be moved between two positions as indicated by arrow B in Figure 2. Lever 20 is pivotally mounted and is also fixed via shaft 21 to the gear box or the cabinet, and is connected to the motor 2 or subsidiary gear box 10, so that when the lever is moved from one position to another this will slidably move the motor 2 (and subsidiary gear box 10). In one position of the lever the motor drive is connected into the gear box 1 while in another position of the lever the motor is moved to the position shown in broken lines in Figure 3, to disconnect the motor drive from the gear box, and in particular to disengage the gears 13 and 14. Thus when the actuator is operated manually by rotating the manual drive shaft 17 via crank handle 10, the motor will not be back driven.

Normally the electric motor 2 (and subsidiary gear box 10) and gear box 1 will be in the lower position shown in hard outline in Figure 3, so that a remotely transmitted radio signal to the actuator will energise the motor 2 to open or close the circuit

breaker. The expression"radio signal"is intended to also include use of the cellular telephone or paging network for example, in which event the radio receiver will comprise or include a cell phone or pager unit. A linesman at the pole may manually actuate the circuit breaker by opening the cabinet, operating the lever 20 to move the motor 2 (and subsidiary gear box 10) to disengage the motor drive from the gear box, and fitting the crank handle 11 to the manual drive shaft and rotating the handle to manually open or close the circuit breaker. Typically the linesman will open the circuit breaker for maintenance or fault finding, and subsequently close the circuit breaker, replace the crank handle, and re-lock the cabinet.

Variations to the preferred form described and illustrated in the drawings are possible. For example gear 18 may engage gear 14 instead of gear 16. In the preferred form the lever mechanism 20 moves the electric motor 2 (and subsidiary gear box 10) relative to the gear box 1 but is as alternatively possible that the lever mechanism may move the gear box 1 relative to the electric motor 2, or both of the electric motor 2 and gear box 1 relative to one another.

The foregoing describes the invention including a preferred form thereof. Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated in the scope hereof as defined in the accompanying claims.