FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
Electrical device locking mechanism
2. APPLICANT(S)
(a) NAME : Larsen and Toubro Ltd.
(b) NATIONALITY: Indian
(c)ADDRESS : L&T House, Ballard Estate, Mumbai-400 001, India.
3. PREAMBLE TO THE DESCRITION
PROVISIONAL COMPLETE
The following specification describes The following specification particularly describes the
invention invention and the manner in which it is to be performed
4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble -
"I/We claim" on separate page)
6. DATE AND SIGNATURE (to be given on the last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on the
separate page)
Note:
*Repeat boxes in case of more than one entry
*To be signed by the applicants)or the authorized registered patent agent
*Name of the applicant should be given in full, family name in the beginning
*Complete address of the applicant should be given stating with postal index no. / code, state and
country
*Strike out the column which is/are not applicable

Electrical device locking mechanism Field of invention
The present invention relates to an apparatus for safely and conveniently locking an individual electrical device like circuit breaker in the OFF or ON position as desired without interfering the other circuit breakers in the panel.
Background of the invention
Circuit breaker is a protecting device and it is used for making, breaking and carrying the current under normal operating conditions. Circuit breaker breaks the circuit under abnormal conditions thus isolates healthy system from the faulty system. Pad-lock or locking devices adds to the functioning of the basic breaker in terms of reliability, safety and protection.
These devices get mounted inside a board or panel board for added safety to the operator. Most often these devices are required to be operated either from outside or by opening the enclosure/ panel.
In view of maintenance person safety, locking device is used which locks the operating knob of the circuit breaker in OFF position. Maintenance person can unlock the operating knob and switch ON the circuit breaker. Multi locks can also be used in case there are more than one maintenance person on the floor. In such cases every person can lock the MCCB in OFF position to carry out the maintenance and unlock the MCCB once maintenance is completed, last person removes his lock and switch ON the circuit breaker.
Now a day's trip free mechanisms are used in molded case circuit breakers where tripping mechanism is independent of the knob position of the circuit breaker. Site supervisor will only be having the key to the lock. By doing so he can avoid

unwanted confusion among people which circuit breaker to be switched OFF & which to switch ON.
In some applications where uninterrupted supply is required such as medical instruments used in Intensive Care Units of hospitals, Computer servers and data centers etc, it is necessary to lock the operating knob in the ON position and therefore prevent access to the operating handle.
In some application, locks are used by electricity board or utilities at customer site to prevent use of electricity to those who have not paid their out standings.
Pad lock can be used as a mechanical Interlocking device (with unique key for the locks) when two breakers are at a distance to avoid the paralleling of two supply sources.
US 6396008 describes a circuit breaker including a housing; separable contacts; an operating mechanism having a movable operator handle with an OFF position and an ON position; and a handle lock device. The handle lock device includes: a member secured to the housing, a flange on the member disposed alongside the operator handle, an opening in the flange adapted to receive only one shackle and having a perimeter which includes first opposing portions adapted to receive a cross section of a safety lockout shackle and to restrain rotation of the shackle within the opening. The shackle blocks movement of the operator handle from the OFF to the ON position thereof. The perimeter also includes second opposing portions adapted to alternatively receive the different cross section of a shackle of a padlock with that shackle blocking movement of the operator handle from the OFF to the ON position thereof. However the arrangement is complex and it is one way operation i.e. it blocks movement of handle from OFF to ON position.

US 6472620 describes a locking arrangement for use on a draw-out mechanism mounted on a circuit breaker within a switchgear cabinet includes a fixed side plate arranged for mounting within switchgear cabinet, a mobile side plate includes a pin extending threrefrom, the mobile side plate arranged to move the circuit breaker in cooperation therewith and an obstructor plate pivotally mounted to the fixed sideplate, the obstructor plate having a slot and a notch extending from the slot, the pin traversing the slot to allow the mobile side plate to move relative to the fixed side plate. However this mechanism is restricted to draw-out type breaker and not intended to provide a locking mechanism which can lock the breaker in either ON or OFF position.
US 6791040 describes a locking assembly is for a circuit breaker. The circuit breaker includes a housing enclosing separable contacts and an operating mechanism. The housing has an elevated portion with an opening. An operating handle, which operates to open and close the separable contacts, protrudes from the opening and moves between "on" and "off circuit breaker positions. The locking assembly includes first and second locking elements pivotally connected to the operating handle and structured to engage the elevated portion of the circuit breaker housing, in order to restrain movement of the operating handle from either the "on" or "off position when the shackle of a lock is inserted through shackle-receiving apertures of the first and second locking elements. Although this provides a locking arrangement which works in both ON and OFF conditions, the arrangement is complex and needs more mechanical elements. Object of the invention
One object of the present invention is to provide a locking system for circuit breaker operation, to lock the circuit breaker to one of the ON and OFF position. Another object of the present invention is to provide a sliding arm with an oblong slot for offsetting the centre of rotation of sliding arm away from knob and locking it in ON or OFF position without interfering with the knob.

Yet another object of the present invention is to provide a slide arm retaining
mechanism which helps in retaining the original position of the sliding arm by doing
both rotational as well as translational motion.
Summary of the invention
The locking mechanism consists of a sliding arm with an oblong slot on its surface
connected to the base plate using a rivet which passes through an oblong slot and a
torsion spring wound around the rivet connects the sliding arm to base plate. The
base plate is provided with plurality of slots for positioning it around the knob,
indicators and mounting it on breaker. The sliding arm moves around the rivet and
end of the sliding arm can be locked when the device is in ONN or OFF position and
when the lock is opened the sliding arm exhibits rotational and translational motion
due to force exerted by torsion spring.
Description of drawings:
Fig 1: Front view of circuit breaker locking device
Fig 2: Exploded view of circuit breaker locking device
Fig 3: Front view of circuit breaker locking device in both locked & normal condition
Fig 4: Operation of circuit breaker locking device
Fig 5: Circuit breaker with 3 locks in normal position
Fig 6: Circuit breaker with 3 locks in locked position
Fig 7: Circuit breaker locked in ON position
Fig 8: Circuit breaker locked in OFF position
Detail description:
The various embodiments of the present invention provides a locking system for
circuit breaker operation, to lock the circuit breaker to one of the ON & OFF
position.
The circuit breaker locking mechanism majorly comprises of four components: Base
plate, sliding arm, torsion spring and rivet.

Circuit breaker locking mechanism is fixed on the midcover of the circuit breaker with the help of four screws. Base plate is formed into a platform with two side steps which contains the through holes. Base plate can be mounted irrespective of the operating knob position of the circuit breaker. Sliding arm is fixed on the base plate with the help of the rivet. Torsion spring is used for retaining the original position of the sliding arm. An oblong slot is provided in the sliding arm which helps in the rotational as well as translational motion of the sliding arm. The oblong hole helps in offsetting the centre of rotation of sliding arm away from knob, thus making it possible to have locking in ON and OFF position without interfering with the knob. During forward translational motion torsion spring stretches itself against the rivet and during backward translational motion, it de-stretches itself and rotate sliding arm back to its original position. Further motion of sliding arm is restricted by the bend provided in the base plate which acts as a mechanical stopper.
For locking through holes are provided in both, base plate and sliding arm. To lock the circuit breaker in any of the two positions ON/OFF, sliding arm is rotated and moved towards base plate hole. After matching both the holes, the circuit breaker is locked with the help of pad lock.
To unlock the operating knob, it is required to remove the lock from both the holes. Tamper proof screws can be used for fixing the locking device on the midcover of the MCCB. The screw head is designed in such a way that it will have narrow cross section beneath the screw head which will get sheared off after application of excessive tightening torque above the specified torque. After breakage of screw head it cannot be removed by any other means. This unique screw design makes the design of circuit breaker locking system temper proof. ON-OFF-TRIP markings on the cover of the MCCB are seen from the window provided in the base plate, this avoids the use of additional label on locking device.

The mechanism uses a sliding arm having an oblong slot which provides both rotational as well as translational motion of sliding arm. The oblong hole helps in offsetting the centre of rotation of sliding arm away from knob, thus making it possible to have locking in ON and OFF position without interfering with the knob. A torsion spring is used to connect sliding arm to the base plate which helps in retaining the original position of the sliding arm by doing both rotational as well as translational motion. During forward translational motion torsion spring stretches itself against the rivet and during backward translational motion; it de-stretches itself and then rotate back to its original position.
A window is provided on the base plate of locking device to make MCCB ON-OFF-TRIP markings visible. Shape of the sliding arm can be modified to suit for multi-locking arrangement for MCCB. Circuit breaker locking device can be used for mechanical interlocking. Circuit breaker locking device can be used in standard door cut out for the frame size of MCCB. Design of circuit breaker locking device is tamperproof and tease proof. Tamper proof screws can be used for fixing the circuit breaker locking device on the midcover of MCCB. The screw head is designed in such a way that it will have narrow cross section beneath the screw head which will get sheared off after application of excessive tightening torque above the specified torque. After breakage of screw head it cannot be removed by any other means. This screw head can be designed in any shape. This unique screw design makes the design of circuit breaker locking system temper proof.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various

embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We claim:
1) An electrical device locking mechanism comprising:
a base plate, the base plate having plurality of holes on its surface;
a sliding arm, the sliding arm having an oblong slot on its surface, and mounting
the sliding arm on the said base plate using a rivet passing through the oblong
slot on the surface of sliding arm and corresponding hole on the surface of base
plate;
a torsion spring wound around the said rivet and ends of the torsion spring fixed
in the said base plate; and
a mechanical stopper in the form of a bend on the surface of said base plate for
restricting the motion of the said sliding arm;
Wherein, the sliding arm can be rotated around the said rivet for locking the
electrical device in ON or OFF position by stretching the said torsion spring; and
when unlocked, the sliding arm exhibits combination of rotational and
translational motion by de-stretching the torsion spring and motion of the rivet
along the oblong slot.
2) An electrical device locking mechanism of claim 1 wherein, oblong slot offsets the centre of rotation of sliding arm away from the knob and locking in ON and OFF position without interfering with the knob.
3) An electrical device locking mechanism of claim 1 wherein, the electrical device is a circuit breaker.
4} An electrical device locking mechanism as described in any of the accompanying drawings.