Electrical Safety

What is Electricity?Electricity is the movement of electrons.Fundamental quantities include:VoltsCurrentResistance

Basic Electrical Theory Voltage [driving force] causes current [e - ] to flow

AC / DC - from safety perspective - negligible difference Single Phase / Three Phase. 3 get a professional

Circuit / loop is necessary for current to flowa start point - a route - an end point January 2008 Ver 1.1*

January 2008 Ver 1.1

Voltage, Current and ResistanceVoltage increases => Current increases Resistance decreases => Current increasesVoltage = Current / Resistance - Ohms Law January 2008 Ver 1.1*

The complete circuit A complete Circuit or loop is necessary for current to flowJanuary 2008 Ver 1.1*

A complete circuit complete Circuit or loop is necessary for current to flowJanuary 2008 Ver 1.1* Current takes the path of least resistance

Basic Electrical Theory Voltage causes a Current to flow

Water analogy

A complete Circuit is necessary for current to flowBird on HT wires January 2008 Ver 1.1*

Voltages Low Tension0 => 50VBatteries: AA, AAA, MP3 playerCar, trucks, busses 12 / 24 / 48Garden lights, domestic halogen lights

High Tension100 => 300VEU Mains, Electrophoresis, DART, Capacitors SM PSUs

Very High Tension1KV +ESB pylons, TV tubes, photocopiers, X-Ray machines, Mass Spectrometers January 2008 Ver 1.1*

January 2008 Ver 1.1

Electricity - associated Hazards Indirect InjuryFalls from ladder Thrown back. Fall to ground, onto sharp edgeDrop objectsThermal burns Very hot equipment surface, explosion

Wires & cables - Trailing leads => trips & damage, Re-route, tidy up, cover over

Life Support musclesDiaphragm and breathing Heart Fibrillation Random, uncoordinated heart contractionsDe-fribrillation: High voltages (3000 V at 20 A) fraction of a second

Burns - death of tissue Internal [organs] External [skin]

January 2008 Ver 1.1*

January 2008 Ver 1.1

January 2008 Ver 1.1* Electrical cables & plugsMains cable

Live power Neutral EarthLN

January 2008 Ver 1.1* Live, Neutral, Earth & Fuses

January 2008 Ver 1.1

January 2008 Ver 1.1* Live, Neutral, Earth & FusesLN

January 2008 Ver 1.1

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January 2008 Ver 1.1* RCD Residual Current Device RCCB Residual Current Circuit BreakerELCB Electric Leakage Circuit BreakerMCB Magnetic Circuit Breakers RCBO Residual Current Breaker with Overcurrent protection current difference of >30 mA for a duration of >30 msLNELN

January 2008 Ver 1.1*Live, Neutral, Earth & Fuses The Live and Neutral wires carry current around the circuit

The Earth wire is there to protect you. The Earth wire can act like a back-up Neutral wire, Many appliances have metal cases e.g. kettles, toasters, dishwashers, washing machines etc.

The Fuse is very thin piece of wire. The wire has a quite low melting point. As current flows through the wire it heats up.If too large a current flows it melts, thus breaking the circuitUse appropriate fuse size/rating

Additional safety devices - RCDs, ELCBs, MCBs

January 2008 Ver 1.1

January 2008 Ver 1.1*Specific Hazards & Personal Safety RF & W Capacitive coupling, no need to touch, Both can burn severely internally and externally depending on how focused. Think of them like an open air -wave oven

HTStatic, OK [Very low current, moderate power]Will jump considerable distances, beware of capacitors

PowerHeating effect in body => internal burns / damageContact burns, deep burns & necrosis

Trailing power and signal wires - Protect & Tidy them up

January 2008 Ver 1.1

Electrical AppliancesSafety guiding principle keep currents and voltages inside apparatus and away from our bodies

Inherently safe - Low voltage / low currentEnclosures InsulationSafe & secure connectionsJanuary 2008 Ver 1.1*

January 2008 Ver 1.1

Electrical cables & plugs Mains cableBrown Live - power Blue Neutral Green/yellow EarthJanuary 2008 Ver 1.1*

Common HazardsShocks.Burns.Explosions.Fires.

Electricity and the Human Body~1ma:Sensation on hands.>3ma:Painful shock which can cause indirect accidents.>10ma:Muscle contraction, no-let-go danger.>30ma:Lung paralysis>50ma:Possible ventricular fibrillation.100ma - 4A: Certain ventricular fibrillation

Protective TriangleKeep AwayGroundingGFCI

Electrocution TriangleElectricityPathTime

FatalityAn employee received a fatal electric shock while operating a high pressure water sprayer which was connected to a portable light with a receptacle built into the handle. The portable light was being used as an extension cord, and was not approved for wet or damp locations. The electrical cord had been spliced and the cord had been laying in water at the time of the accident.

Fatality

Commonly Cited ViolationsUnused openingsExposed live partsMissing coversDefective GroundProhibited uses of flexibl cords.

Blocked Electrical Panels

Strain on Conductors

Inadequate Strain Relief on Cord

Exposed Live PartsEmployees cap is hung on power strip energized to 120VAC

Exposed Live Parts

Exposed live partsMissing breakers inside of circuit breaker panel

Ungrounded CordsGround pin missing on extension cord

Damaged Faceplate

Utility BoxesUtility boxes are not approved for usage as extension cords.

Receptacles in Wet LocationsReceptacles in wet or damp locations need covers.

Receptacles in Wet LocationsReceptacles in wet or damp locations need covers.

Damaged Faceplate

Portable Electric ToolsInspect before usage.Remove from service tools with damaged cords.Use grounded or double insulated tools.Check continuity of tool.

Hazard AssessmentEmployers are required to assess the workplace to determine if hazards that require the use of personal protective equipment are present or are likely to be present.

Personal Protective EquipmentHead protection - overhead hazardsEye protection - grinding, chipping, or sawing operations.Hearing protection - noisy environmentsRespiratory protection - exposure levels exceed permissible exposure limits.Foot protection - falling, rolling, or sharp object.

Rubber GlovesMust be air tested daily before usage.Must be electrically tested every 6 months or replaced.Before issuance gloves may be stored for up to 1 year without being tested.

Ground fault circuit interrupters (GFCIs)A GFCI is not an overcurrent device like a fuse or circuit breakerGFCIs are designed to sense an imbalance in current flow over the normal path

Ground fault circuit interrupters (GFCIs)GFCI contains a special sensor that monitors the strength of the magnetic field around each wire in the circuit when current is flowingThe field is proportional to the amount of current flow

If the current flowing in the black (ungrounded) wire is within 5 milliampers of the current flowing in the white (grounded) all the current will flow in the normal pathIf the current flow differs by more than 5mA +/- 1mA, the GFCI will quickly open the circuit Ground fault circuit interrupters (GFCIs)

Low-resistance grounding systems use a neutral grounding resistor to limit the fault current to 25 A or greater.

Low resistance grounding systems will have a time rating (e.g. 10 seconds) that indicates how long the resistor can carry the fault current before overheating. A ground fault protection relay must trip the breaker to protect the circuit before overheating occurs.

High-resistance grounding (HRG) systems use an NGR to limit the fault current to 25 A or less.

They have a continuous rating, and are designed to operate with a single-ground fault.

This means that the system will not immediately trip on the first ground fault.

If a second ground fault occurs, a ground fault protection relay must trip the breaker to protect the circuit. On an HRG system, a sensing resistor is used to continuously motor system continuity. If an open-circuit is detected (e.g., due to a broken weld on the NGR), the monitoring device will sense voltage through the sensing resistor and trip the breaker.

***Shocks:Occurs when electrical current flows through parts of the body. Results can be:a.Indirect (falling from ladders, scaffolds, b.Direct (damage or death caused by the flow of electricity through the body.

Burns: Are usually caused by excessively hot electrical conductors (as in heaters or faulty wiring) or by arc blasts. Arc blast occurs from high amperage currents arcing through the air after contact has initiated large current flows, as in short circuits.

Explosions: Can be caused when electricity provides a source of ignition for an explosive mixture in the atmosphere. Excessively high conductor temperatures, or normal arcing-sparking at switch contacts, can provide this ignition source. The removal of electrical equipment or installation of explosion proof can prevent explosions.

Fires: Are most commonly caused by deterioration of insulation on bad or old wiring, defective or misused appliances, loose connections and misused devices.*Let Go current is that current above which one cannot let go of the conductive surface being grasped. This causes involuntary contraction of both extensor and flexor muscle groups. Because flexors are stronger than extensors, the resultant effect is that one cannot extend or let go.

*Keep Away:Insulation, Elevation, Isolation, Buried, Covered.Grounding:Provides current with a low resistance path. GFCI:Will not prevent a shock, but is designed to prevent a fatal shock.

Remember current will take all paths to ground.*In order to receive a shock you must have electricity, a path, and time. All three must be present. The longer the duration the more severe the injury**Several employees were trying to isolate a shortage problem in the plant before lunch. The problem resulted in some lights and several machines going out. Maintenance personnel used a volt meter to check fuses in the main switch box. The employees checked the continuity of the 3 fuses, and then switched the meter to 1000VAC and attempted to measure the voltage across the top of the switch. An explosion occurred and 2 employees were burned and the third was killed. Switch voltage was 13,200VAC.

Employees were not trained in Electrical Safety Work Practices, Employees did not utilize rubber gloves, or mats. Employees were not qualified to work on energized parts. *1 - 1910.305(b)91):Conductors entering boxes not protected against abrasions. Unused opening in boxes not effectively closed. {611}2 - 1910.303(g)(2):Exposed live parts {553}3 - 1910.305(b)(2):Electrical boxes missing covers {485}4 - 1910.304(f)(4):Grounding path not permanent and continuous {454}5 - 1910.305(g)(1)(iii):Prohibited uses of flexible cords and cables.

Prohibited uses include:Used in place of fixed wiring.Run through walls, doorways, windows or similar.Attached to building surfaces.Concealed behind building walls, ceilings, or floors. **********