Frequently Asked Questions...
Why do I keep blowing the definate purpose contact switch in my central AC unit?
I have an older central AC unit for my home and the "definite purpose contactor" switch keeps going out. If I push the switch down by hand the compressor engages and pumps cold air, but the switch itself keeps going out. When the switch went out last season I replaced it and it stayed working for about a week. Hoping it was a fluke I replaced it again, but with the same results. I have resorted to keeping the switch engaged with a stick and turning my AC unit off at the main power box by hand, but this is getting to be a real pain.
Any advice on this matter would be very helpful as I am really hoping I can avoid calling out the repair man.
Thanks!
Answer:
I have a few questions for you first..#1 is the your unit a split system (blower and heater one place and the compressor located another?) or dual pack (heating and cooling in one cabinet) #2 is the bad contactor pulling the contacts together or not? #3 do you know how to use a volt ohm meter?
 NEW SIEMENS DEFINITE PURPOSE CONTACTOR 45EG20AJ 2 POLE HVAC US $19.99 
|
 Qty-10,Definite Purpose Contactor (Type: DP) 20A, 2-Pole, 1-Phase, Non-Reversing US $55.00
|
 Contactor Definite Purpose 2 Pole FLA:25 Coil 208/240 US $6.76
|
 A-1 Components Definite Purpose Contactor A30AMP 2P 24V US $11.50
|
 MARS DEFINITE PURPOSE CONTACTOR 685744 91321 2 POLE 30 AMP 3390D HVAC PART INBOX US $9.99
|
 Definite Purpose Contactor 120vac coil, 3 pole contacts US $40.00
|
 SCHNEIDER ELECTRIC DEFINITE PURPOSE CONTACTOR 8910DP31V14 US $30.00
|
 WHITE ROGERS 2 POLE DEFINITE PURPOSE CONTACTOR 90-244/122-901 US $20.00
|
 Square D Definite Purpose Contactor 8910DP31V14 US $25.00
|
 FURNAS 75D54822F MAGNETIC COIL - FOR DEFINITE PURPOSE CONTACTOR US $39.99
|
 Dayton Definite Purpose Contactor 2UTP4 3P 50A US $37.39
|
 Furnas Definite Purpose Contactor X13070073010 / 42AF35AFAES (USED) US $14.99
|
 Mars 2 Definite Purpose Contactor NEW in Box 17425 US $14.99
|
 FURNAS 75D54772J 24V COIL/DEFINITE PURPOSE CONTACTOR US $28.00
|
 Definite Purpose Contactor 42CE35AJZ106 by Siemens-Furnas US $35.00
|
 New 30 amp 3 pole 24 vac Definite Purpose Contactor UL US $12.99
|
 New 30 amp 3 pole 120 vac Definite Purpose Contactor UL US $12.99
|
 #A-1 COMPONENTS DEFINITE PURPOSE CONTACTOR A30 AMP 2P 24V US $16.99
|
 NEW FURNAS 42BE35AG106 DEFINITE PURPOSE CONTACTOR 3P 30A 208/240V COIL US $25.00
|
 DEFINITE PURPOSE MARS 3 POLE CONTACTOR, 40 AMP, 120V COIL, NEW IN THE BOX, 91432 US $28.00
|
 Furnas 3 Pole Definite Purpose Contactor 24 Volt Coil, FL 30 RES 40, New in Box US $25.00
|
 Contactor, Definite Purpose, 2 Pole FLA: 20 Coil 120 VAC, SUPCO # DP201202 US $6.95
|
 DEFINITE PURPOSE CONTACTOR 2 POLE / 30 AMP / 24 VOLT (BRAND NEW) US $7.15
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 50 AMP / 110-120 VOLT (BRAND NEW) US $30.97
|
 DEFINITE PURPOSE CONTACTOR 2 POLE / 40 AMP / 600 VOLT (BRAND NEW) US $7.49
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 30 AMP / 110-120 VOLT (BRAND NEW) US $11.85
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 30 AMP / 24 VOLT (BRAND NEW) US $11.83
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 40 AMP / 110-120 VOLT (BRAND NEW) US $12.25
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 40 AMP / 600 VOLT (BRAND NEW) US $12.25
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 50 AMP / 24 VOLT (BRAND NEW) US $30.97
|
 DEFINITE PURPOSE CONTACTOR 3 POLE / 40 AMP / 24 VOLT (BRAND NEW) US $12.25
|
 FURNAS CONTACTOR Definite Purpose Controller 240 480V US $159.00
|
 Square D 8910 DP11V14 Definite Purpose Single Pole Contactor US $28.00
|
 Q.E. Definite Purpose Contactor 2 POLE / 40 AMP / 24 VOLT. / 50/60 Hz (NEW) US $7.20
|
 HVAC TRUCK STOCK - DEFINITE PURPOSE CONTACTORS 30 AMP US $59.00
|
 HVAC TRUCK STOCK - DEFINITE PURPOSE CONTACTORS 40 AMP US $69.00
|
 1 NEW SQUARE D 8910DP32V14 DEFINITE PURPOSE CONTACTOR US $49.99
|
 NIB Honeywell Tradeline DP3030B5002 Definite Purpose Contactor US $19.95
|
 Contactor Definite Purpose 1.5 Pole FLA: 30 Coil: 24 V US $6.65
|
 MARS Definite Purpose Contactor 91733 US $79.99
|
 Furnas Definite Purpose Controller 45GG10AJAL1 Contactor US $20.00
|
 Furnas Definite Purpose Controller 45EG20AJ (61345) Contactor US $20.00
|
 Furnas Definite Purpose Controller 42BF35AJBBV Contactor US $30.00
|
 DEFINITE PURPOSE CONTACTOR 2 POLE 30 AMP 240V COIL - A/C HEAT PUMP TRANE RHEEM US $9.95
|
 DEFINITE PURPOSE CONTACTOR 2 POLE 40 AMP 120V - Coil 120 VAC A/C HEAT PUMP TRANE US $10.16
|
 DEFINITE PURPOSE CONTACTOR 3 POLES 30 AMP 24V A/C HEAT PUMP TRANE RHEEM US $14.95
|
 DEFINITE PURPOSE CONTACTOR 3 POLES 40 AMP 24V A/C HEAT PUMP TRANE RHEEM US $16.95
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 40 AMP 120V COIL - A/C HEAT PUMP TRANE RHEEM US $17.95
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 30 AMP 120V COIL - A/C HEAT PUMP TRANE RHEEM US $14.99
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 40 AMP 240V COIL - A/C HEAT PUMP TRANE RHEEM US $18.95
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 50 AMP 24V COIL - A/C HEAT PUMP TRANE RHEEM US $28.25
|
 DEFINITE PURPOSE CONTACTOR 3 POLES 50 AMP 120V A/C HEAT PUMP TRANE RHEEM US $28.70
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 50 AMP 240V COIL - A/C HEAT PUMP TRANE RHEEM US $28.95
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 60 AMP 24V COIL - A/C HEAT PUMP TRANE RHEEM US $32.95
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 60 AMP 240V COIL - A/C HEAT PUMP TRANE RHEEM US $32.95
|
 NEW Siemens Definite Purpose Contactor 42BF35AGAHY US $40.00
|
 Honeywell/Tradeline Definite Purpose 3 Pole Contactor 40 FLA 208/240V Coil, New US $25.00
|
 Furnas/Siemens Definite Purpose 3 Pole Contactor 30 Amp 208-240V Coil, New inBox US $14.99
|
 DEFINITE PURPOSE CONTACTOR 3 POLE 60 AMP 120V COIL - A/C HEAT PUMP TRANE RHEEM US $32.95
|
 Furnas Definite Purpose 3 Pole Contactor 60 FLA 75 RES 208/240V Coil, New US $40.00
|
 FURNAS 42BE35AJ106 DEFINITE PURPOSE MAGNETIC CONTACTOR US $65.00
|
 FURNAS 42EE35AF106 DEFINITE PURPOSE MAGNETIC CONTACTOR US $150.00
|
 Eaton Definite Purpose Contactor C25ANB125T US $19.99
|
 FURNAS 42BE35AG106 DEFINITE PURPOSE CONTACTOR, 208-240 VOLT COIL US $24.95
|
 WILSPEC CT CT3XU02CY Definite Purpose Contactor 30FLA US $25.00
|
 HONEYWELL DP1040A 5004 DEFINITE PURPOSE CONTACTOR US $12.95
|
 NEW BREAKERS UNLIMITED BU302U10 DEFINITE PURPOSE CONTACTOR 2 POLE 30FLA 24VAC US $33.25
|
 NEW HARTLAND CONTROLS HC302U10 DEFINITE PURPOSE CONTACTOR 2 POLE 30FLA 40A RES US $33.25
|
 New 30 amp 2 pole 120 vac Definite Purpose Contactor UL US $8.50
|
 New 30 amp 2 pole 24 vac Definite Purpose Contactor UL US $8.50
|
 New 40 amp 2 pole 24 vac Definite Purpose Contactor UL US $10.50
|
 New 40 amp 2 pole 240 v coil Definite Purpose Contactor US $10.50
|
 New 40 amp 3 pole 24 v coil Definite Purpose Contactor US $16.99
|
 New 40 amp 3 pole 240 v coil Definite Purpose Contactor US $16.99
|
 Contactor Definite Purpose 2 Pole FLA:20 Coil 208/240 US $6.62
|
 Square D 8910DPA12V14 Definite Purpose Contactor US $20.00
|
Definite Purpose Contactor
INDIAN ELECTRICITY RULES AND INDUSTRIAL SAFETY
Paramesh Malakar.
B. Sc. (Engineering), BHU
INDIAN ELECTRICITY RULES AND INDUSTRIAL SAFETY
Indian Electricity Rules are very broad and wide guidelines for design, manufacture, construction, operation and maintenance of all electrical installations and Industrial Safety rules are inbuilt into it. These rules, being the body to cover all aspects of Electricity seems to be, at many a point, ambiguous and extraneous. However, an in-depth interpretation of these rules indicates the elements that need compliance to have a proven system to strong, reliable and safe.
It is felt to be utmost importance to discuss the safety aspects of electricity as electricity in various forms has become indispensable to the modern industry for maintaining propriety of generation, drive, control, communication, , announcement, safety and managing disasters.
Generation and handlings of power is given primary emphasis in this article as these are considered injurious to apparatuses and life.
An approach here is made to proceed from basic needs in simple language so that the contents are accessible to nonprofessionals also along with engineers since many such persons are being engaged in electrical work.
CONTENTS:
INTRODUCTION
CLASSIFICATION OF AREAS
MAJOR COMPONENTS OF INDUSTRIAL INSTALLATIONS
IMPORTANT RULES
GENERAL SAFETY ASPECTS
SELECTION OF APPARATUSES
INSTALLATION OF APPARATUSES
CAPACITY UTILIZATION AND OPERATION
ROUTINE HEALTH CHECKUP
MAINTENANCE OF STATISTICS
PERSONNEL SAFETY RULES
INTRODUCTION
Safety at the dawn of civilization was included in the three basic needs. Food, Shelter and Clothing gave man the safety he needed. Inventions and the development the inventions brought about in mechanizing man’s ways demanded more safety. Safety took birth as a concept and to-day it has become a branch of engineering studies. Speaking commonly about safety is to imply use of safety appliances like welding goggles or radiation shields while doing welding or operating X-ray machines. However, if hazards of discharges, explosions, accidental contacts, possibility of lightning etc. are considered it will become apparent that safety considerations are to begin with design of machines and systems and are to be systematically inbuilt through manufacturing, installation and operation of plants and equipments.
The hazards faced are unpredictable and inestimable. But, while dealing with industrial hazards it is seen that these hazards are contained in definite and demarcated systems. In case the deficiencies of a system are known these can be eliminated by suitable design and working procedures.
Electrical safety aspects of industrial installations are related mainly to healthy operation during running, abnormal shutting down, switching in and out and maintenance working. Such electrical safety is not difficult to ensure if proper approach is adopted from blue-print-stage.
CLASSIFICATION OF AREAS
An industry is a unit, which processes inputs to obtain final product ? output. The nature of environment at different locations inside the industrial area is continuously changed due to abnormal operation and generation of wastes and pollutants. These locations may become HAZARDOUS from the point of view of electrical engineering depending on their degree of flammability. It is very essential that only proper electrical appliances and apparatuses are chosen for such areas which are turned hazardous by plant processes. Again rain, humidity, dust are also harmful for electrical installations.
Area, which does not have any risk of fire in their environment, is safe. In such safe area apparatuses designed and manufactured to meet the rated duty can be installed. However, where risk prevails the areas are hazardous. Hazardous areas of industrial installations are grouped into Divisions (Ref. IS5572) depending upon the presence occurrence of flammable gas or gas mixtures in ion it.
These are:
DIV 0: Where risk of fire is constantly present.
DIV I: Where risk of fire is present during normal operating condions.
DIV II: Where risk of fire is present during abnormal operating conditions.
- These areas demand different safe features to be built into in electrical apparatuses as integrated features to make these suitable for such locations.
- In Div 0 areas electrical apparatuses, as far as practical should be avoided. However, if at all necessary flammability in the area is to be precisely defined and intrinsically safe units are to be installed.
- In Div I and II areas where explosive gas concentration is present but is within limit FLAMEPROOF APPARATUSES ( Ref IS 2148) or INCREASED SAFETY APPARATUSES (Ref. IS 6318) are to be used.
- Areas where rainfall, foreign matter and humidity become matter of concern enclosures of electrical apparatuses are to be WEATHER PROOF ? e.g., as per IS 4691 for induction motors, IS 2147 for LV switchboards and suitably protected against entry of foreign matter as contained in these standards. Electrical apparatuses are also available in pressurized, non-sparking, weatherproof etc type for installation and use in specific areas.
MAJOR COMPONENTS OF INDUSTRIAL INSTALLATIONS
Industrial electrical installations mainly comprises of : a) Outdoor indoor sub stations, b) HV MV switchboards, c) LV PCCs & MCCs, d) Transformers, e) Motors, f) cable network, g) Overhead lines, h) switching stations, i) heaters, j) refrigerators, k) lighting systems etc. For safety of these, certain rules in the IE Rules are laid down. These are to be meticulously adhered to.
IMPORTANT RULES
The important clauses are:-
- IE Rule 29: Rule 29 make provision for ample power handling capacity, size, and strength. This rule says that any electrical apparatus, network or system must have sufficient capacity to handle the power energy required to do the specific job, its size must be adequate to handle the power requirement and must be convenient for use and it must have sufficient mechanical strength to avoid danger to human life or items in immediate vicinity.
- IE Rule 50: Rule 50 makes provision for application of suitable switches, breakers on primary, secondary sides of transformers, controllers of motors and use of suitable insulating materials.
- IE Rule 66: Rule 66 provides for metal-sheathed conductor system or for cable network the level of fault currents available to the rating of feed isolating switchgear or fuse gear on occurrence of fault.
- These IE Rules include electrical apparatuses for handling and use of electrical power and consider the aspect of amply designing and manufacturing these items. Such is also gets envisaged that suitability of use application of these is taken taken care of during blue print stage. These rules taken together with relevant Indian Standards grants details, which need consideration regarding safety of apparatuses in use.
- In addition to setting broad guidelines for manufacturing, I E Rules also provides for installation and testing of electrical apparatuses and systems; and various safety measures to be adopted while erection and commissioning is hand.
- IE Rule 51 : Rule 51 provides for sufficient inbuilt mechanical strength of electrical apparatuses, enclosing electrical live parts in earthed metal enclosures and installation guidelines as to permissiveness of space near switchboards for movement of working personnel.
- Rule 60,61 : Rule 60, 61 make it necessary to earth properly the electrical systems and testing it to ensure tat installations do not have hidden defects.
- Rule 64, 66, 67 : these rules make it necessary to have safety incorporated into the installations by means of protections, safety drains and soak pits, for transformer oil, preventing oil accumulation in trenches, arranging layouts such that faulty electrical component can be isolated immediately. These also provide for various tests regarding voltage withstand ability and insulation condition to ensure system capability to withstand over voltages and handling safely the fault currents. These also take care regarding safe earthing of electrical systems at different locations to avoid danger.
GENERAL SAFETY ASPECTS
The general safety aspects of industrial installations are to take care of the followings at different stages:-
SELECTION OF APPARATUSES
During selection :
- Classification of areas.
- Selection f apparatuses suitable for the particular area.
- Taking proper care against possible misinterpretation of short descriptions like ? fire proof, flame proof, weather proof, submersible, relative humidity etc. and to properly establish their relation to actual working environment.
- Taking proper note to the short time and continuous duty ratings and relating the various operating parameters to the limiting values for safe working.
INSTALLATION OF APPARATUSES
During Installation :
- Name plate and Rating plate details to be related to the apparatuses and their proper installation referring to relevant IS Standard wherever applicable.
- The working safety of the location and proximity to other equipments for safe working and maintenance.
- Cable terminations and all connections should be of suitable type and size done by approved methods.
- Details designed for earthing and lightning arresters systems shold be strictly followed and any deficiency in execution should be compensated by addition alteration as necessary. Due care is to be taken to neutral apparatus earthings.
- Location of control gear to any electrical apparatus must be so positioned that it remains accessible during abnormality of apparatus or any other plat abnormality.
- Care is to be taken to prevent rain water accumulation and flowing in of surface water into cable trenches.
CAPACITY UTILIZATION AND OPERATION
These broad guidelines and rules thus direct to wards establishing proper relation between the final use and capacity evaluation during design, manufacturing, selecting proper typr for use in different environment, steps to be taken during erection installation to make these safe. However, one point is of great importance here as to see how long the apparatus in operation remains intact and manufacturer maintains good margin and some critical properties of electrical apparatuses are lost durin ng operation. Some of these are :-
- Di-electrical and physical properties of insulation.
- Spring tension of various contacts and resulting contact pressure.
- Ohmic resistance of electrical joints and terminations connections.
- Calibration of protective and measuring instruments and apparatuses.
In this instance while attention is on suitable capacity and suitable selection the author remembers two instances :-
- On a motor – control – centre (MCC) a control fuse was blown in a motor switchgear compartment. Immediately no fault was detected, so the fuse , due to non availability of HRC fuse was rewired and put back. The neutral link was in position. The fault was lurking in the power contactor coil because of inter - turn short. Immediately on insertion of the fuse it blew with heavy sound and caused flash – over on the sleeved bus bars with naked joints running right behind the fuse base. Result was a burn injury to operator’s hand and plant tripping. This is a clear indication of risk involved in over sizing fuses.
- In another instance, there was a short circuit on LT switchgear. There the ACB compartment bakelite shutters were riveted to metal strips. While withdrawing the ACB one strip came out, touched bus bars, caused short circuit with heavy arc and fire. Such was the result of wrong selection and application during design and manufacturing. Later on, these strips were replaced with insulated bars.
ROUTINE HEALTH CHECKUP
Ageing of electrical apparatuses is a considerable phenomenon. In case of insulation the deterioration of electrical strength may be major consideration in one application (e.g. transformer, reactor) but again loss of mechanical strength may become the major factor in another. For example: the physical strength of insulation is of prime consideration for increased safety motors, bus bar support insulators, line insulators etc. In normal practice a GO NO GO indication is monitored on insulation of electrical apparatuses by hand held meggar. But it is necessary that quality measurements are made at specific intervals.
Another hidden danger in aged insulation is that it becomes dry, looses heat carrying capacity and results in development of hot spots. In case of motors it is very critical since motors at times are subjected to repeated starts. The effect if insulation ageing in transformer is a complicated phenomenon. In addition to insulation stresses developing due to high temperature, here the insulation gets exposed moisture and sludge produced in the transformer in the normal operation. As the transformer ages moisture and sludge formation increases in rapidity. So condition evaluation or residual life evaluation of transformers in operation is highly essential tests as otherwise the transformer may be stressed to limit of fire and explosion on occurrence of any minor spark.
Industrial installations may have an earthing network with an earthing grid system. This grid system is essential to equalize earth potential, control step and touch voltages to within limited values. The grid system contains earth pits and earth strip network and includes equipment neutral earths. During operation, the joints develop resistances. Such resistances remain undetected during earth resistance testing. However, on dead earth faults the fault current distribution gets impaired, flows through routs of least resistance and in occasion leads to melting of connections at points nearest to transformer. This phenomenon becomes pronounced in case of the location of industry records high rainfall. Water corrodes the jointing bolts, makes the connection loose and also grants fault current paths through electrolytic action. During the time from fault inception to line isolation the fault current travels unpredictably and flows into transformer or generator neutral through the nearest earth pit which remain in direct connection with the transformer or generator neutral. The author has experiences of earth pit connection failure of 25 MVA 66 11 kV transformer neutral end due to earth fault at overhead distribution system. In such instances the feeder was not isolated at Feeder OCB, not isolated at Incomer OCB but the 66 kV feeder tripped on O/C detection at the sending end. Such occurrences are causes of concern as oil accumulation is often noticed in switchyard and transformer station pits and may cause fire. Such neutral disconnections can give rise to high voltage phenomenon if faulty system remains connected and may cause injury to the electrical installations.
Changes or departures of characteristics of protective relays in use or getting stuck of moving components of relays in use is not uncommon. Regular checking and calibration of these items are necessary. Protective devices like Buchholz relay on transformers, fire (over temperature) sensing devices to release CO2 cylinders if fails to perform may result in accidents and damage of severe nature. These protective devices are to be kept healthy at all times.
Electrical safety aspects of industrial installations are best considered during design and manufacturing. Such keeps the plants in safe running state. However, plants need operation and maintenance. Electrical safety to working staff is equally important.
MAINTENANCE OF STATISTICS
It is necessary that accident and abnormal occurrence information are collected and framed into statistical data to indicate the influence of various factors. For example, table 1 below give the accident figures in percentage expressions. This table indicates a) the voltage class of installations where fatal accidents are numerous, b) age group of working staff who are more susceptible to accidents, c) type of installations or locations where accidents are more frequent.
TABLE 1
A.
TYPE OF INSTALLATION --AND-- NO. OF FATAL ACCIDENTS
AS VOLTAGE CLASS %
- H. V. sub – stations 96%
- L. V. sub - stations 4%
B.
AGE GROUP OF WORKMEN -- AND—NO. OF FATAL ACCIDENTS
%
20 – 25 YEARS 9%
25 – 30 YEARS 15%
30 – 35 TEARS 18%
35 – 40 YEARS 19 %
40 – 45 YEARS 9%
45 – AND ABOVE 30 %
C.
TYPE OF INSTALLATION -- AND -- NO. OF FATAL ACCIDENTS
HIGH VOLTAGE LOW VOLTAGE
Over head lines 15% 5%
Accidental contact 16% 3%
General appliance - 15%
Domestic uses - 11%
Sub station equipment 8% 0.5%
Agricultural uses - 8%
Portable lamps - 7%
Consumer’s service lines - 5%
Portable power tools - 3%
Misc 1% 2,5%
PERSONNEL SAFETY RULES
Every one recognizes that plant safety riles are invaluable. Once the statistics is prepared or practical, approach is to be adopted in framing the rules with proper judgment based on experience and knowledge. In industries whenever a new technique is developed new problems appear. Safety rules must be kept abreast of the times.
CERTFICATION OF PERSONNEL
SELECTION OF WORKERS FOR ELECTRICAL JOB IS VERY VITAL. These persons must be suitable for electrical job and and must have the requisite qualification and right attitude for accident prevention. They are supposed to know wheather job taken up conforms to rules and time tested work practices.
INTERACTION OF SUPERVISORS
Maintenance work may necessitate simultaneous jobs to be taken up on different fronts as an integrated network. For example, work may become necessary on a transformer, its HV side breaker and L V side incoming bus duct. In such a situation, there must be thorough understanding of the scope of job among the groups. This makes it essential that supervisors assemble in a conference and take stock of the details of each job.
COMPOSITION OF TEAM
It is very important that work team consist of the required manpower only. Over or under manning is undesirable. Small teams are preferable. So work planning should be such that small teams are engaged in specific jobs and whenever required small teams are combined to get more workforce.
OPERATIONAL INSTRUCTIONS
While working on H V or M V apparatuses these are isolated from thr source and are made ‘dead’.
But in certain cases of L V systems like industrial control circuits, at times lighting circuits and in providing temporary connections, work is taken up on live circuits.
Again there is cable demands consideration of the whole tray as live to the voltage level of the live cable.
OPERATION OF ELECTRICAL INSTALLATIONS AND LOCK OUT PROCESSES
In taking electrical circuits out of service it is imperative that effective steps are taken to ensure that it can not be accidentally re-energized. One visible break must be made and it must be suitable ‘tagged’. Safety rules must be strictly observed and wherever locks have been provided their use must be mandatory.
COMPLETING MAINTENANCE OPERATIONS
During maintenance work various temporary connections are provided for hand tols, portable lamps etc. These remains as dangerous connections if not removed on completion of maintenance work. Care should be taken for proper accounting of all temporary connections.
PERSONAL PROTECTIVE MEASURES.
Personal protective measures to be adopted by working staff are to be taken up with utmost care. It should be kept constantly in mind by the supervisor that his staff members may have some human problem like not getting information about his son who is studying at a far off place, his mind may be preoccupied by his wife’s sickness or he may be constantly thinking about buying a new model car. Whatever it maybe, his preoccupation r anxiety should come to the notice of his supervisor who in turn will take care of the personal outfit of the team member.
The safety measures those form part of general precaution are;
- All workmen should wear clothing which will enable them free movement and yet are close fit.
- Workmen should not wear shoes with wailed soles.
- Workmen should not use cap with metal frames.
- Workmen should not wear rings.
- Workmen should not carry keys, coins, any metal parts on them in open pockets.
- Workmen should not use spectacles with metallic frames.
RUBBER GLOVES.
Rubber goloves suitable y insulated for the voltage of line or equipment on which work is to be carried out, must be worn by workmen. However, it must be born in mind rubber gloves only does not qualify working on live lines.
Ordinary rubber coats , boots, shoes, hats etc. should not be considered as protective insulation.
While using rubber gloves care must be taken thst spark or arc can not run through it and worker’s hand remains save from contact with live parts.
SAFETY BELTS
Safety belts must be used while working in locations at a height where ample space and means for support is not available.
Safety belts must be used while working at a height if the worker is to use both his hands.
INSULATED TOOLS
Tools used by electricians (e.g. pliers, tong-testers, fuse pullers etc. ) should be insulated.
The same worker may need to perform the duties of electrician and technicians. In such cases electrician’s tools must be separately kept and properly used.
LADDERS.
Suitable ladders must be used wherever necessary. It shall be borne in mind that taking support from items on walls and roofs which are not meant for such purposes is a dangerous practice.
MAINTENANCE OF PERSONAL MEASURES
Tools and protective devices equipments to be used by workers needs be periodically tested and kept such that its condition does not deteriorate in keeping.
About the Author
P. Malakar.
B.Sc.(Electrical Engineering), 1971.
Industrial Exp. in Field and Management of Elect.Engg.for 30+ yrs.
interested in behaviour of machines and their protections.
Age;59 yrs.
Here are a list of other products on Woodturning Tools, come check these out:
