CASE STUDY 3

INTRODUCTION 

An excellent introduction to electrical safety, this course provides instruction in electric shock protection, prevention of electrical injuries and working in hazardous conditions. Instruction takes place both in the classroom and in Seta’s state-of-the-art workshop facilities.

This course is ideally suited  to those who wish to work safely in the presence of electricity.

                           

THE DEFECTIVE INSULATION HAZARDS

                            IMPROPER GROUNDING HAZARDS 

 Before 1996, it was common practice to use the neutral as an equipment ground. Now, however, all frames of common household appliances such as electric ranges, clothes dryers, wall mounted ovens, and countertop mounted cooking panels must be grounded by a fourth wire, an equipment grounding conductor. If you still have an old appliance in place, the best course of action is to run a new 4-wire branch circuit from the panel. The neutral if used as an equipment grounding conductor should be removed.

OVERLOAD HAZARDS

Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components in an electrical system or circuit have a maximum amount of current they can carry safely. If too many devices are plugged into a circuit, the electrical current will heat the wires to a very high temperature. If any one tool uses too much current, the wires will heat up.

The temperature of the wires can be high enough to cause a fire. If their insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall.

In order to prevent too much current in a circuit, a circuit breaker or fuse is placed in the circuit. If there is too much current in the circuit, the breaker “trips” and opens like a switch. If an overloaded circuit is equipped with a fuse, an internal part of the fuse melts, opening the circuit. Both breakers and fuses do the same thing: open the circuit to shut off the electrical current.

If the breakers or fuses are too big for the wires they are supposed to protect, an overload in the circuit will not be detected and the current will not be shut off. Overloading leads to overheating of circuit components (including wires) and may cause a fire. You need to recognize that a circuit with improper overcurrent protection devices—or one with no overcurrent protection devices at all—is a hazard.

Overcurrent protection devices are built into the wiring of some electric motors, tools, and electronic devices. For example, if a tool draws too much current or if it overheats, the current will be shut off from within the device itself. Damaged tools can overheat and cause a fire. You need to recognize that a damaged tool is a hazard. 

WET CONDITION HAZARDS

Working in wet conditions is hazardous because you may become an easy path for electrical current. If you touch a live wire or other electrical component—and you are well-grounded because you are standing in even a small puddle of water—you will receive a shock.

Damaged insulation, equipment, or tools can expose you to live electrical parts. A damaged tool may not be grounded properly, so the housing of the tool may be energized, causing you to receive a shock. Improperly grounded metal switch plates and ceiling lights are especially hazardous in wet conditions. If you touch a live electrical component with an uninsulated hand tool, you are more likely to receive a shock when standing in water.

But remember: you don’t have to be standing in water to be electrocuted. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted. You need to recognize that all wet conditions are hazards. 

PREVENTIVE ELECTRICAL HAZARDS

PROTECTION FROM DIRECT CONTACT

The methods of preventing direct contact are mainly concerned with making sure that  people cannot touch live conductors. These methods include: 1. - the insulation of live parts - this is the standard method.  The insulated conductors should be further protected by sheathing, conduit, etc. 2. - the provision of barriers, obstacles or enclosures to prevent touching.  Where surfaces are horizontal and accessible, IP4X protection  (solid objects wider than 1 mm are excluded). 3. - placing out of reach or the provision of obstacles to prevent people  from reaching live parts 4. - the provision of residual current devices (RCDs) provides supplementary  protection but only when contact is from a live part to an earthed part.              PROTECTION FROM INDIRECT PROTECTION An indirect contact refers to a person coming into contact with an exposed-conductive-part which is not normally alive, but has become alive accidentally (due to insulation failure or some other cause). The fault current raise the exposed-conductive-part to a voltage liable to be hazardous which could be at the origin of a touch current through a person coming into contact with this exposed-conductive-part (see Fig. F3). IEC 61140 standard has renamed “protection against indirect contact” with the term “fault protection”. The former name is at least kept for information

TO CREATE A SAFE WORKING ENVIRONMENT

 LOCK OUT TAG OUT CIRCUITS AND EQUIPMENT 

Lockout is defined in the Canadian standard CSA Z460-13 "Control of Hazardous Energy - Lockout and Other Methods" as the "placement of a lockout device on an energy-isolating device in accordance with an established procedure." A lockout device is "a mechanical means of locking that uses an individually keyed lock to secure an energy-isolating device in a position that prevents energization of a machine, equipment, or a process."

Lockout is one way to control hazardous energy. See the OSH Answers Hazardous Energy Control Programs for a description of the types of hazardous energy, and steps required in a control program.

In practice, lockout is the isolation of energy from the system (a machine, equipment, or process) which physically locks the system in a safe mode. The energy-isolating device can be a manually operated disconnect switch, a circuit breaker, a line valve, or a block (Note: push buttons, selection switches and other circuit control switches are not considered energy-isolating devices). In most cases, these devices will have loops or tabs which can be locked to a stationary item in a safe position (de-energized position). The locking device (or lockout device) can be any device that has the ability to secure the energy-isolating device in a safe position.

OVERLOAD WIRING BY USING THE RIGHT SIZE AND TYPE OF WIRE

Control hazards of fixed wiring

The wiring methods and size of conductors used in a system depend on several factors:

• Intended use of the circuit system
• Building materials
• Size and distribution of electrical load
• Location of equipment (such as underground burial)
• Environmental conditions (such as dampness)
• Presence of corrosives
• Temperature extremes

Fixed, permanent wiring is better than extension cords, which can be misused and damaged more easily. NEC requirements for fixed wiring should always be followed. A variety of materials can be used in wiring applications, including nonmetallic sheathed cable (Romex®), armored cable, and metal and plastic conduit. The choice of wiring material depends on the wiring environment and the need to support and protect wires.

Aluminum wire and connections should be handled with special care. Connections made with aluminum wire can loosen due to heat expansion and oxidize if they are not made properly. Loose or oxidized connections can create heat or arcing. Special clamps and terminals are necessary to make proper connections using aluminum wire. Antioxidant paste can be applied to connections to prevent oxidation.


Control hazards of flexible wiring

Use flexible wiring properly

Electrical cords supplement fixed wiring by providing the flexibility required for maintenance, portability, isolation from vibration, and emergency and temporary power needs.

Flexible wiring can be used for extension cords or power supply cords. Power supply cords can be removable or permanently attached to the appliance. 

Use the right extension cord

The size of wire in an extension cord must be compatible with the amount of current the cord will be expected to carry. The amount of current depends on the equipment plugged into the extension cord. Current ratings (how much current a device needs to operate) are often printed on the nameplate. If a power rating is given, it is necessary to divide the power rating in watts by the voltage to find the current rating. For example, a 1,000-watt heater plugged into a 120-volt
circuit will need almost 10 amps of current. Let’s look at another example: A 1-horsepower electric motor uses electrical energy at the rate of almost 750 watts, so it will need a minimum of about 7 amps of current on a 120-volt circuit. But, electric motors need additional current as they startup or if they stall, requiring up to 200% of the nameplate current rating. Therefore, the motor would need 14 amps.

Add to find the total current needed to operate all the appliances supplied by the cord. Choose a wire size that can handle the total current.

WHAT WILL HAPPEN IF WE NOT CONTROL ELECTRICITY?

→ IT WILL CAUSE OF DEATH DURING THE MAINTENANCE

→SHOCK CIRCUIT WILL HAPPEN

→THE BUILDING WILL GO ON FIRES

→A WASTE OF ELECTRICITY

CONCLUSION

The control of electrical hazards is an important part of every safety and health program. The measures suggested in this booklet should be of help in establishing such a program of control. The responsibility for this program should be delegated to individuals who have a complete knowledge of electricity, electrical work practices, and the appropriate OSHA standards for installation and performance. Everyone has the right to work in a safe environment. Through cooperative efforts, employers and employees can learn to identify and eliminate or control electrical hazards.