How shall all electrical apparatus be selected, installed, placed and protected?
(21.1.1.1) All electrical apparatus shall be selected, installed, worked, marked and maintained in such a manner as not to constitute a hazard and shall be placed and protected in such a manner that no person can be injured by inadvertent contact with any live part thereof.
A new substation is being designed for surface electrical distribution. The building is to be constructed of clay brick and will have metal doors. What will you, as the engineer in charge, require of the design to ensure that the building meets with the regulations? (What are the provisions of the regulations with regard to size, construction, illumination, live parts, doors and fire protection of a place where electric apparatus is installed?)
(21.1.2) Any place where electrical apparatus is installed and which may constitute a danger to persons shall be:
- Fenced off or enclosed effectively.
- Provided with notices at all entrances prohibiting unauthorized access and
- Kept closed and locked at all entrances, if unattended by an authorized person to prevent unauthorized access.
(21.1.3) Any fenced off or enclosed place shall be:
- Of adequate size to provide safe and unobstructed working space.
- Constructed and ventilated in such a manner that the apparatus is kept at a safe temperature.
- Constructed in such a manner to provide protection against the inlet of water.
- Illuminated in such a manner to prevent any danger to persons and to enable all equipment to be distinguished clearly and all instruments, labels and notices to be read clearly while it is live.
- Constructed in such a manner that no live parts are within reach of windows or wall openings, and
- Designed in such a manner as to provide, in an emergency, an unobstructed outlet from a door which shall not open inwards and such door shall be provided with notices on both sides.
When may a cable trench be left open?
(21.2) No cable trench shall be left open, uncovered or unprotected except at a place where work is being carried out in such trench.
What protection is required on electrical apparatus which may endanger persons as a result of a fault?
(21.3.1) Electrical apparatus in which a fault may develop which may endanger persons shall be provided with effective switching, controlling or protective devices which, in the event of a fault, shall automatically isolate the power supply to such apparatus.
(21.7.3) Where an earth fault give rise to a condition dangerous to persons, adequate electrical protection shall be provided.
How shall electric switching or controlling apparatus, which is accessible from the front and the back, be marked?
(21.3.2) The markings shall be on a fixed portion of the front and the back.
What is required where a ring feed or a possibility of back feed exists at any electrical apparatus?
(21.3.3) Where a ring feed or the possibility of electrical back feed exists at any apparatus a prominent notice to that effect shall be fixed to such apparatus.
When may a person interfere with electrical apparatus provided for safety or protection?
(21.4) No person shall interfere with or render ineffective any electrical apparatus provided for safety or protection unless it is necessary to do so to perform work associated with such apparatus.
What shall the minimum clearance be in front of any switchboard?
(21.5.1) A switch board shall have a clearance of not less than 1.2 m in the front for operating and maintenance purposes.
You wish to install an electrical switchboard to which access from the back is required. What clearances must be allowed?
(21.5.3) Any switchboard to which access is required from the back and which has no live conductors accessible from the back when the panels enclosing the back are in position shall have a clearance of at least 0.75 m at the back and such space shall not be obstructed in any manner.
(21.5.3.1) Any switchboard of which the back is accessible only through an opening in a wall against which it is placed shall have a clearance at the back which shall be sufficient for the purpose of electrical insulation between conductors and the wall. The opening in the wall shall be kept closed and locked to prevent unauthorized entrance.
Describe the requirements for a switchboard which has live conductors accessible only from the back and has no doors, covers or panels enclosing the back?
(21.5.4) Any switchboard which has live conductors accessible from only the back and that has no doors, covers or panels enclosing the back shall have a clearance of at least 1.2 m behind it. Such space shall not be obstructed and access to such space shall only be permitted when the conductors are dead and the access shall only be through doors which shall be kept closed and locked.
May examination, adjusting, testing or repairs on live electrical apparatus be done?
(21.6.1) No examination, adjustment, testing, repair or other work necessitating the dangerous approach to or handling of electrical apparatus shall be carried out unless such apparatus are dead. Where the apparatus must be live for the purpose of examination, adjustment, testing, repair or other work it may be done by or under the direct supervision of a competent person.
Who may enter a place where electrical apparatus is installed?
(21.6.2) No person other than an authorized competent person shall enter a place where electrical apparatus is installed unless all live conductors are insulated or otherwise protected against contact. An authorized competent person may in an emergency be assisted by a person acting under the immediate supervision of such authorized competent person.
What precautions shall be taken when work is to be carried out on electric apparatus that has been isolated from all sources of supply?
(21.6.3) Whenever work is to be carried out on electric apparatus which has been isolated from all sources of supply, effective precautions shall be taken by earthing to prevent any conductor from being made live accidentally while any person is working thereon.
What ladder may be used when working with electricity?
(21.6.4) No metal ladder or ladder with metal stiles may be used for examination, repair or other work necessitating the dangerous approach to or work on electrical apparatus.
If an accessible metallic portion of an electric plant which does not normally form part of an electrical circuit may accidentally become live, how must it be protected?
(21.7.1) Any accessible metallic portion which does not normally form part of an electrical circuit but which may accidentally become live shall be protected by insulating material or shall be connected to earth by a conductor of adequate cross-sectional area so as to prevent danger to persons.
State the provisions of the regulations with regard to the following:
1) The cross-sectional area of an earth conductor
(21.7.2) The cross-sectional area of any earthing conductor shall be capable of withstanding the maximum possible earth fault current.
2) Earth fault protection
(21.7.3) Adequate electrical protection shall be provided where an earth fault may lead to dangerous conditions to persons.
3) Un-insulated live conductors near a fixed ladder way, landing or walkway.
(21.8.4) No portion of any un-insulated or unprotected live electrical apparatus or conductor shall be permitted within a horizontal distance of 1.5 m or within a vertical distance of 3 m from any landing, walkway or permanently fixed ladder way.
Describe the requirements of any lattice type support which carries overhead conductors?
(21.8.1) Any lattice type support which carries overhead conductors shall be protected adequately to prevent any unauthorized coming into dangerous proximity to the person from conductors by climbing up such support: Provided that the principle inspector of mines may require that a support of any other type shall be protected similarly.
Describe the requirements for the connection of an overhead service line to a line conductor? (Describe the requirements where any overhead service line passes a building, structure or any place from which access is possible?)
(21.8.2) Every overhead service line shall be connected to a line conductor at a point of support only and every portion of such service line which is accessible from a building or from a ladder leaning against a building shall consist of suitable insulated wire.
What signs are required at places where live overhead power lines cross roads and where shall these signs be situated?
(21.10.6) Notices and signs indicating the maximum height of any object permitted to pass beneath a live overhead power line shall be displayed at suitable places not less than 150 m from the point where such objects is likely to pass beneath such line.
Where the maximum height of an object is greater than the permissible height indicated on any notice or sign, what is the legal procedure for the movement of the object below the power lines?
(21.10.7) The person in charge of the movement shall stop the movement and inform the responsible engineer or competent person appointed in terms of regulation 2.13.2 and such engineer or competent person shall thereafter supervise any movement of such object.
When may a machine with a movable or extendable boom be used in close proximity to overhead power lines?
(21.10.8) Any machine with a movable or extendable boom may be operatedin close proximity to overhead power lines only if:
- The operator of such machine is competent and has been authorized by the engineer or person appointed in terms of regulation 2.13.2, and
- The clearance between any part of the machine or its load and the overhead powerline complies with the minimum clearance as specified according to the regulations, or
- The power lines are disconnected and earthed, or
- The power lines are shielded against any contact by any part of the machine or its load.
What are the requirements for any structure supporting a crossing span of an overhead power line?
(21.11.1) Any structure supporting a crossing span shall be:
- Designed to be able to withstand any load imposed by the breakage of any phase or earth.
- As far as practicable be located in such a manner that it will not touch the service crossed when overturned.
- One of the structures supporting a crossing shall be as close as possible to the point of crossing.
- Where a power line crosses a road the clearance above the ground shall not be less than 5 m in the case of a broken phase conductor in a span other than the crossing span.
- A crossing span shall not have any joints.
- When the voltage exceeds 1.1 KV: –
- Armour rods shall be fitted at the live ends of the suspension and insulators on at least the first three structures on both sides of the crossing.
- Duplicate conductors, tied together every 1.5 m, shall be provided in the crossing span and supported by duplicate parallel insulators.
- The deviation from a right angled crossing over a communication line shall not be greater than: – 30º for a 48 KV line or higher.
- 45º for a line less than 48 KV.
Give the minimum clearance allowed when an overhead service main crosses any bare overhead communication line.
(21.11.2.2) Any overhead service main shall not cross underneath bear communication lines.
What wind pressure value is assumed a line conductor and structure is subjected to?
(21.12.2) It is assumed that the line conductor and structure is subjected to a pressure of 700 KPa.
What is the minimum allowable factor of safety of any line conductor?
(21.12.3.1) The factor of safety of any line conductor shall not be less than 2.5 and based on the rated ultimate tensile strength of the conductor.
What electrical cables shall be protected with armouring?
(21.14.1) Any cable other than a trailing cable, a cable of an intrinsically safe circuit or a flexible cable for movable electric apparatus shall be protected by armouring if:
- The cable is buried directly in the ground.
- The cable is installed in such a position that mechanical damage may occur.
- There may be risk of igniting gas or other flammable material.
When may a flexible cable or trailing cable be used?
(21.14.2) A flexible cable or trailing cable may only be used in connection with the operation of:
- Any self propelled mobile machine which requires electric power to operate.
- Movable electric apparatus, or
- Portable electric apparatus.
Describe the requirements of screening and joints regarding flexible and trailing cables?
(21.14.3) Any flexible cable or trailing cable shall be screened either individually or collectively and such screens shall be earthed.
(21.14.4) No flexible or trailing cable shall have more than fifteen joint repairs, including sheath patches, over a length of 200m, and
- No joint or patch shall be closer than 5m to another joint or patch, and
- No joint or patch shall be closer than 3m to the cable plug or terminal connection at the machine or apparatus.
What are the requirements of the regulations regarding flexible and trailing cables used in a hazardous area?
(21.14.3) Any flexible cable or trailing cable used in a hazardous area shall be screened individually and such screens shall be earthed.
(21.14.6) Any flexible trailing cable used in a hazardous area shall be:
- Provided with a intrinsically safe pilot circuit which will prevent power from being supplied to the cable unless the earth conductor is in a good working condition, and
- Provided with a means of preventing arcing of contacts of any plug being inserted or withdrawn, and
- Connected to a supply on which the earth fault current is limited to prevent danger to persons.
What are the requirements of cable reels on self propelled mobile machines?
(21.14.5) Any cable reel used on a self propelled mobile machine shall be provided with a device which shall interrupt the power supply before the complete cable is unreeled so that at least one complete turn of the cable shall remain on the reel unless the machine’s maximum range of travel is limited to less than permitted by the cable on the reel.
What are the requirements for any installation in a hazardous area?
(21.15) Any cable shall be placed in such a manner that it cannot be damaged.
The engineer shall appoint a competent person who shall carry out:
- At least once a month at intervals not exceeding 45 days a thorough examination and test for continuity of all electrical apparatus and every earth conductor, transformer neutral earthing system, armouring or screening, except in cases where a continuous earth monitoring system has been installed or a equivalent system has been approved by the principle inspector, and
- An examination and test of all new and re-erected apparatus before it is put into service. The person carrying out the examination or tests shall record the results in a logbook which shall be scrutinized and countersigned by the engineer.
What are the requirements of electrical wiring of buildings situated on a mine?
(21.16) At every mine or works all buildings situated therein shall be wired in accordance with a code of practice approved by the principle inspector of mines.
Briefly describe the procedure to be followed when explosion protected apparatus are supplied to a coal mine and the engineer wants to ensure that the apparatus complies with the statutory requirements?
(21.17)
- The manager shall identify and record any hazardous area on a plan.
- All electrical apparatus used in a hazardous area shall be explosion protected and certified as such in a test report by an inspection authority approved by the chief inspector of mines.
- An identification nr shall be allocated to such equipment.
- The manager shall have a copy of the test report.
- The identification nr shall be clearly marked on the apparatus or on a metal plate (other than a light metal) and permanently fixed.
- Before use a copy of the test report shall be send by the manager to the principle inspector of mines who may enforce restrictions and conditions.
What are the manager’s duties in connection with persons operating explosion protected apparatus?
(21.17.6) The manager shall take all reasonable measures to ensure all persons operating, running and maintaining explosion protected apparatus are instructed in the specifications in which the apparatus was tested.