Electrical Safety NFPA 70E

Electrical SafetyNFPA 70E

How Electricity Works Operating an electric switch is like turning on awater faucet. Behind the faucet or switch theremust be a source of water or electricity withsomething to transport it, and with a force tomake it flow. In the case of water the source is a pump, andthe force to make it flow through the pipes isprovided by the pump. For electricity, the source is the powergenerator. Current travels through electricalconductors (wires) and the force to make it flow,measured in volts, is provided by a generator.

Basic Electrical Terminology Current: the movement of electrical charge Resistance: opposition to current flowmeasured in ohms Voltage: a measure of electrical force Conductors: substances, such as metals, thathave little resistance to electricity Insulators: substances, such as wood, rubber,glass, and bakelite, that have high resistance toelectricity Grounding: a conductive connection to theearth which acts as a protective measure

Dangers of Electricity On average, a workeris electrocuted everyday Causes 12% of youngworker workplacedeaths Takes very littleelectricity to causeharm Significant risk ofcausing fires

Effects on the Human Body 1 mA: Can be felt by the body 2-10 mA: Minor shock, might result in a fall 10-25 mA: Loss of muscle control, maynot be able to let go of the current 25-75 mA: Painful, may lead to collapseor death 75-300 mA: Last for 1/4 second, almostalways immediately fatal

Types of Electrical Injuries There are four main types of electricalinjuries:– Electrocution (death due to electricalshock)– Electrical shock– Burns– Falls

If Electrocution Occurs Call for helpDO NOT touch the victim or the conductorShut off the current at the control boxIf the shutoff is not immediately available, usea non-conducting material to free the victim If necessary and you know how, begin CPRwhen current is stopped In dealing with electricity, never exceed yourexpertise

Electrical Shock Received when currentpasses through the body Severity of a shockdepends on:– Path of current throughthe body– Amount of currentflowing through thebody– Length of time the bodyis in the circuit

Dangers of Electrical Shock Currents greater than75 mA* can causeventricular fibrillation(rapid, ineffectiveheartbeat) Will cause death in afew minutes unless adefibrillator is used 75 mA is not muchcurrent – a smallpower drill uses 30times as much

How Electrical Shock is Received When two wires have different potentialdifferences (voltages), current will flow if they areconnected together– In most household wiring, the black wires areat 110 volts relative to ground– The white wires are at zero volts becausethey are connected to ground If you come into contact with an energized (live)black wire, and you are also in contact with thewhite grounded wire, current will pass throughyour body and YOU WILL RECEIVE A SHOCK

How Electrical Shock is Received If you are in contact with an energized wireor any energized electrical component,and also with any grounded object, YOUWILL RECEIVE A SHOCK You can even receive a shock when youare not in contact with a ground– If you contact both wires of a 240-voltcable, YOU WILL RECEIVE A SHOCKand possibly be electrocuted

Electrical Burns Most common shockrelated, nonfatal injury Occurs when youtouch electrical wiringor equipment that isimproperly used ormaintained Typically occurs onthe hands Very serious injurythat needs immediateattention

Falls Electric shock canalso cause indirect orsecondary injuries Workers in elevatedlocations whoexperience a shockcan fall, resulting inserious injury or death

Controlling Electrical Hazards Most electricalmishaps are causedby a combination ofthree factors: Unsafe equipmentand/or installation, Workplaces madeunsafe by theenvironment, and Unsafe work practices

Clues that Electrical Hazards Exist Tripped circuit breakers or blownfuses Warm tools, wires, cords,connections, or junction boxes GFCI that shuts off a circuit Worn or frayed insulation around wireor connection

Inadequate Wiring Hazards A hazard exists when aconductor is too small to safelycarry the current Example: using a portable toolwith an extension cord that hasa wire too small for the tool– The tool will draw morecurrent than the cord canhandle, causing overheatingand a possible fire withouttripping the circuit breaker– The circuit breaker could bethe right size for the circuitbut not for the smaller-wireextension cordWire GaugeWIREWire gauge measureswires ranging in size fromnumber 36 to 0 Americanwire gauge (AWG)

Control – Use the Correct Wire Wire used dependson operation,building materials,electrical load, andenvironmentalfactors Use fixed cordsrather than flexiblecordsMust be 3-wire type and designed for Use the correcthard or extra-hard useextension cord

Overload Hazards If too many devices areplugged into a circuit, thecurrent will heat the wiresto a very hightemperature, which maycause a fire If the wire insulationmelts, arcing may occurand cause a fire in thearea where the overloadexists, even inside a wall

Grounding Hazards Metal parts of an electrical wiring system that wetouch (switch plates, ceiling light fixtures,conduit, etc.) should be at zero volts relative toground Housings of motors, appliances or tools that areplugged into improperly grounded circuits maybecome energized If you come into contact with an improperlygrounded electrical device, YOU WILL BESHOCKED

Overhead Power Line Hazards Most people don’t realize thatoverhead power lines are usuallynot insulated Power line workers need specialtraining and personal protectiveequipment (PPE) to work safely Beware of power lines when youwork in the vicinity with ladders,erecting antennae, movingequipment, etc.

Preventing Electrical Hazards Ways of protecting workers and preventingelectrical hazards trical protective devicesSafe work practices

Insulation Check insulation priorto using tools andequipment Remove from serviceany tools or equipmentwith damagedinsulation

Guarding of Live Parts Must guard live parts of electricequipment operating at 50 voltsor more against accidentalcontact by:– Approvedcabinets/enclosures– Location or permanentpartitions making themaccessible only to qualifiedpersons– Elevation of 8 ft. or moreabove the floor or workingsurface Mark entrances to guardedlocations with conspicuouswarning signs29 CFR 1910.303(g)(2)(i)(A)

Guarding of Live Parts Must enclose orguard electricequipment inlocations where itwould be exposed tophysical damage– Physical damage toconduit29 CFR 1910.303(g)(2)(ii)

Cabinets, Boxes, and Fittings Junction boxes, pullboxes and fittingsmust haveapproved covers Unused openings incabinets, boxes andfittings must beclosed (no missingknockouts)29 CFR 1910.305(b)(1) and (2)

Grounding Grounding creates alow-resistance pathfrom a tool to the earthto disperse unwantedcurrent When a short orlightning occurs,energy flows to theground, protecting youfrom electrical shock,injury and death

Improper Grounding Tools plugged intoimproperly groundedcircuits may becomeenergized Broken wire or plug onextension cord Some of the mostfrequently violatedOSHA standards

Electrical Protective Devices These devices shut off electricity flow in theevent of an overload or ground-fault in the circuit Include fuses, circuit breakers, and ground-faultcircuit-interrupters (GFCIs) Fuses and circuit breakers are over-currentdevices When there is too much current: Fuses melt Circuit breakers trip open

Ground-Fault Circuit Interrupter The GFCI detects a differencein current between the blackand white circuit wires– This could happen whenelectrical equipment is notworking correctly, causingcurrent leakage known as aground fault If a ground fault is detected,the GFCI can shut offelectricity flow in as little as1/40 of a second, protectingyou from a dangerous shock

Safe Work Practices Never use plugs orreceptacles that canalter polarity Properly plug allconnecting plug-ins Install and useprotective devices Stay away from allunguarded conductors Never overload acircuit or conductor

Safe Work Practices Know where the hazards areProperly maintain equipmentNo exposed parts or energized surfacesUse barriers and devices whereappropriate No conductors to walk on or trip on No jewelry, or other metal objects aroundelectricity

Planning Plan your work withothers Plan to avoid falls Plan to lock-out and tagout equipment Remove jewelry Avoid wet conditions andoverhead power lines

Warn Others Use barricades to prevent orlimit access to work areas withun-insulated energizedconductors or circuit parts If signs and barricades do notprovide sufficient warning andprotection from electricalhazards, an attendant shall bestationed to warn and protectemployees Use safety signs, safetysymbols, or accident preventiontags to warn others aboutelectrical hazards which mayendanger them

Visually Inspect Portable cord and plug connectedequipment and flexible cord sets(extension cords) shall be visuallyinspected before use on any shift forexternal defects:– Loose parts– Deformed or missing pins– Damage to outer jacket or insulation– Evidence of possible internal damage

Remove from Service If there is a defect or evidence of damageto any electrical tools or equipment– Immediately notify your supervisor– Remove the item from service– Tell your co-workers

Working on Energized Equipment Persons working onenergized equipmentmust be familiar with theproper use of specialprecautionary techniques,PPE, insulating andshielding materials, andinsulated tools

Working on Energized Equipment Isolate the area from alltraffic Post signs andbarricades Use an attendant ifnecessary Use insulated tools,mats and sheeting Use electrical rubbersheeting to covernearby exposed circuits

Arc Flash Hazards Electric arcs produce some of the highesttemperatures known to occur on earth – upto 35,000 degrees Fahrenheit. This is fourtimes the surface temperature of the sun. All known materials are vaporized at thistemperature. When materials vaporize theyexpand in volume (Copper – 67,000 times,Water–1670 times). The air blast can spreadmolten metal to great distances with force. Rapidly expanding gases, extreme pressureand sound waves, molten metal and metalplasma.

Arc Flash Hazards Pressure: Blast pressure waves have thrownworkers across rooms and knocked them offladders. Pressure on the chest can be higher than2000 lbs/ sq. ft. – blows clothing off body. Clothing can be ignited several feet away. Clothedareas can be burned more severely than exposedskin if clothing melts. Hearing loss from sound blast. The sound can havea magnitude as high as 140 dB at a distance of 2 feetfrom the arc.

Electrical Arc Flash Burn

Electrical Arc Flash Accident

Arc Flash Causes Dust and impurities - Dust and impurities on insulating surfaces can provide apath for current, allowing it to flashover and create arc discharge across thesurface. Corrosion - Corrosion of equipment creates impurities on insulating surfaces.Corrosion also weakens the contact between conductor terminals, increasingthe contact resistance through oxidation or other contamination. Heat isgenerated on the contacts; sparks may be produced; can lead to arcing faultsclosest ground source. Condensation - water vapor can drip causing tracking on the surface ofinsulating materials. Can create a flashover to ground. Spark discharge – Accidental contact; dropping tools Overvoltage across narrow gaps Failure of insulating materials Improper work procedures

Arc Flash in Our Equipment For a low voltage system (480/277 V), a 3 to 4-inch arc canbecome “stabilized” and persist for an extended period of time. Energy released is a function of system voltage, fault currentmagnitude and fault duration. Arcs in enclosures, such as a Motor Control Center (MCC) orpanelboard, magnify blast and energy transmitted as the blastis forced to the open side of the enclosure and toward theworker (Arc-in-the-Box).