Electictiy

OHM’S LAW

In 1827, George simon ohm discovered that the flow of electric current was directly proportional to the applied voltage and inversely proportional to the “resistance” of the wires of cables (conductors) and the load. This discovery became known as Ohm’s Law.

                                                       

The current in amperes (I) is equal to the electromotive force, or voltage  (V) divided by the resistance (R) in “ohms”

Current (I)   = Voltage (V)

                        Resistance (R)

I                    =   V

                           R

ELECTRICAL HAZARDS

ELECTRIC SHOCK

 An electric shock occurs, when a person comes into contact with electrical energy source. Electrical energy flows thorough a portion of the body causing a shock.

ARC FLASH AND ARC BLAST.

An Arc Flash

Is the light and heat produced from on electric arc supplied with sufficient electrical energy to cause substantial damage.

Arc Blast

Is an explosive blast arises from the intensive radiant heat produced by an arc.

An arc flash or are blast is a type of electrical explosion that result from a low impedance connection to ground or another voltage phase in an electrical system.

• Operating an electric switch is like turning on a water faucet. Behind the faucet or  switch there must be a source of water or electricity with something to transport it, and with a force to make it flow.
• In the case of water the source is a pump, and the force to make it flow thorough the pipes is provided by the pump.
• For electricity the source is the power generator.Current travels thorough electrical conductors (wires) and the force to make it flow, measured in volts, is provided by a generator

ELECTRICAL SHOCK

• Received when  current passes thorough the body( you become part of the circuit)
• Severity of shock depends in :

PATH of current thorough the body

AMOUNT OF CURRENT flowing thorough the body

LENGTH OF TIME the body is in the circuit

IF ELECTROCUTION OCCURS

• Call for help
• Donot touch the victim or the conductor
• Shut of the current at the control box
• If the shut off not possible immediately available, use a not conductor material to free the victim (Cardio pulmonary respiration) when
• If necessary and you know how, begin CPR (resociation) current is stopped
• In dealing with electricity, never exceed your expertise

ELECTRICAL BURNS

• Most common shock-related, non fatal injury
• Occurs when you touch electrical wiring or equipment that is improperly used or maintained
• Typically occurs on the hands
• Very serious injury that needs immediate attention

CONTROLLING ELECTRICAL HAZARDS

• Most electrical mishaps are caused by a combination of three factors :
• Unsafe equipment and / or installation,
• Workplace made unsafe by the environment
• Unsafe work practices

THAT ELECTRICAL HAZARDS EXIST

• Unsafe work practices
• Warm tools, wires, cords, connections, or junction boxes

CLUES

• GFCI that shuts off a circuit
• Tripped circuit breakers or blown fuses
• Worn or frayed insulation around wire or connection

OVERLOAD HAZARDS

• if too many devices are plugged into a circuit, the current will heat the wires to a very high temperature, which may cause a fire
• if the wire insulation melts, arcing may occur and cause a fire in the area where the overload exists, even inside a wall    

PREVENTING ELECTRICAL HAZARDS

INSULATION

• Check insulation prior to using cables tools or equipment
• Remove from service any tools or equipment with damaged insulation
• Cabinets, boxes and fittings
• Junction boxes pull boxes and fittings must have approved covers
• Unused openings in cabinets, boxes and fittings must be closed (no missing knockouts)

GROUNDING

• Grounding creates a low resistance path from a tool to the earth to disperse unwanted current
• When a shorter lightning occurs, energy flows to the ground, protecting you from electrical shock, injury and death

ELECTRICAL PROTECTIVE DEVICES(GFCI GROUND FAULT CIRCUIT INTERRRUPTED)

• The ground fault circuit interrupter or GFCI is a fast acting circuit breaker designed to shut off electric power in the event of a ground fault within as little as 1/40 of a second

IMPROPER GROUNDING

• Tools plugged into improperly grounded circuits may become energized
• Broken wire or plug on extension cord
• Some of the most frequently violated OSHA standards

HAND HELD ELECTRIC TOOLS

• Hand held electric tools pose a potential danger because they make continuous contact with the hand
• To protect you from shock, burns, and electrocution, tools must :

-          Have a three wire cord with ground and be plugged into a grounded receptacle, or

-          Double insulated

PANEL BOXES

Panel boxes are used to house circuit breakers that block or isolate energy

-          ensure panel boxes remain clear

-          label all circuits for what they control

-          label panel boxes for what they control

-          replace circuit breakers with blanks when not in use

PROPER INFORMATION

• Hazards associated with working with electricity
• Stopped breathing is not necessarily dead
• Ventilation should be given only when the breathing has stopped
• 7 out of ten victims of electric shock were revived when artificial respiration
• After three minutes, the chances of revival decrease
• Turning off the supply switch or by removing the plug from its receptacle
• Suspected electrical device may be pulled free of the victim

ELECTRIC CURRENT EFFECTS ON HUMAN BODY

Current	Reaction
Below 1mA	Generally not perceptible
1mA	Faint tingle
5mA	Slight shock felt, not painful but disturbing, average individual can let go ; strong involuntary reactions can lead to other injuries
6 to 25mA (women)	Painful shock, loss of muscular control
9 to 30 (men)	The freezing current or let go range ; individual cannot let go but can be thrown away from the circuit if extensor muscles are stimulated
50 to 150mA	Extreme pain, respiratory arrest, severe muscular contractions ; death possible
1000 to 4300mA	Rhythmic pumping action of the heart ceases ; muscular contraction and nerve damage occur ; death likely
10,000mA	Cardiac arrest, severe burns ; death possible

FACTS

• 97% of all electricians have been shocked or injured on the job
• Approximately 30,000 workers receive electrical shock yearly
• Over 3600 disabling electrical contract injuries occur annually
• Electrocutions are the 4^th leading cause of traumatic occupational fatalities
• Estimates show that 10 ARC-Flash incidents occurs every day in the US
• Information derived from industry surveys, the NFPA, the national safety council, bureau of labor statics and cap schell, inc