Week 11 electricity Flashcards
___workers are electrocuted every week.
five
Causes the deaths of __ of the younger workforce
12%
Direct: 1. Shock, Electrical 2. Electrocution or death due to electrical shock 3. Burns Indirect – 4. Falls 5. Fires 6. Explosions
6 electric hazards
Current through the Body - An electrical shock is received when electrical current passes through the body. YOU are in the “Loop” - You will get an electrical shock if a part of your body completes an electrical circuit by… touching a live wire & an electrical ground, or touching a live wire & another wire at a different voltage.
Hazard 1 electrical shock
Severity of Shock - depends on:
1.Path of current thru the body 2.Amount of current flowing through the body (amps) 3.Duration of the shocking current through the body, LOW VOLTAGE DOES NOT MEAN LOW HAZARD!!!
Currents above ___ can paralyze or “freeze” muscles.
10 mA
Currents more than ___ can cause a rapid, ineffective heartbeat – death will occur in a few minutes unless a defibrillator is used
75 mA
___ is not much current – a small power drill uses 30 times as much
75 mA
milliampere equation
- mA = milliampere = 1/1,000 of an ampere
___ Painful shocks… causing indirect accidents.
3mA+-
___Muscle contraction… “not able to let go”
10mA+-
___Lung paralysis… usually temporary.
30mA+-
___Ventricular Fibrillation… is possible
50mA+-
____ Certain Fatal Ventricular Fibrillation
100mA to 4amp
Over ___ Severe burns, heart paralysis.
over 4 amps
Most common… shock related injury By touching Wires - Touching electrical wiring or equipment that is improperly used or maintained Hands get it - Typically occurs on hands Very serious injury - that needs immediate attention
hazard 3 burns
An Indirect Injury - Electric shock can also cause indirect injuries
Can cause Death - Workers in elevated locations who experience a shock may fall, resulting in serious injury or death
Hazard 4 - Falls
Fires- most commonly caused by current flowing through high resistance due to faulty wiring igniting insulation and / or other material.
Hazard 5 - fires
___ - created from high currents flowing through a wire…
This is analogous to two objects being rubbed together very fast, heat is generated. (At full speed, ‘skin’ of an SST jet is about ___)
- heat
2. 6000 F
heat of friction
To maintain continuity of flow, as the diameter of a pipe decreases, the velocity of the fluid must increase, and the heat of friction increases.
when a wire decreases in ____ due to damage, current must increase through that portion of the wire, & heat increases possibility to the point that surrounding materials are set on fire.
cross-sectional area
Can be caused when electricity provides the ignition source (arc) “jumping” through an air-’fuel’ mixture in the atmosphere.
Explosions hazard 6
The six hazardous electrical conditions
- Exposed Electrical Parts 2. Proximity to Power Lines 3. Inadequate Wiring 4. Defective Cords 5. Poor or No Grounding 6. Overloaded Circuits
Control 1– Isolate Electrical Parts use____
.Conductors going into them must be protected, and unused openings must be closed.
cabinets, boxes fittings
J-boxes (etc) must have approved covers
Unused openings must be closed (no missing knockouts)
Control 1– Close Openings
Lines Do not get near power lines
Watch… Cranes Ladders Scaffolds Backhoes Scissors lifts Raised dump truck beds
Hazard 2- Power Lines
when dealing with power lines keep a ___ feet away from them.
10 feet
mA = milliampere =
1/1,000 of an ampere
control 2 - Power lines
1.Keep Away - 10’ - minimum 2.Post Signs – warning of danger 3.Assume Lines are “Hot” 4.Use No Metal - Use wood or fiberglass ladders, not metal 5. Use PPE - Power line workers need special training & Personnel Protective Equipment
- De-energize before working on them 2.Lock Out/Tag Out; …or Power Provider to deenergize.
- OR Guard OR Insulate lines
Control 2- Above Ground Power Lines
- Always Call “One Call” – before digging
- Always Locate & De-Energize – before digging
- Re-Call “One Call” if in Doubt - If obvious signs of utilities (power boxes, poles etc.) exist but are not marked, call for the locator to re-mark before working.
control 2 underground power lines
Select wire size based on
operation, bldg materials, electrical load, and environmental factors Use fixed cords, not flexible cords Use the correct extension cord
When selecting wire
Must be 3-wire type and designed for hard or extra-hard use
Temporary lighting
Temp Lighting is Temporary, remove it immediately upon completion of construction. Protect Temporary Lights from Breakage, use bulb guards. Don’t “hang” Temporary Lights by wires, unless designed for this use.
Temporary wiring requirements
- Must have Breaker Protection: All branch circuits must come from panel board & have breaker protection.
- NO Temp wiring on floors - Branch circuits cannot be run on floors.
- Wall Outlets must have Covers
- Protect Wiring -Protect conductors entering boxes, etc from abrasion.
- Close Unused Openings - in J-boxes. 6. Close Unused Openings - in J-boxes
- Weatherproof Enclosures - In wet locations.
- Protect Hardware from Water - …Cabinets, boxes, switches, circuit breakers, etc
Causes of damaged cords
- Aging, wear
- Edges of doors, window
- Staples or fastenings
- Abrasion from adjacent materials
- Impact from activity in the area
Extension cord rules
- Use only 3 wire type, hard duty - All extension cords must be 3-wire type & hard or extra hard duty.
- Protect from Damage – must protect flexible cords & cables from damage.
- No “Pinch Points” – must not run cords through pinch points.
- No Nails, Staples, etc – must not suspend extension cords by nails, staples, or wires.
3 steps for cords and wiring protection
- Use Plugs with Ground Pins - Path to ground must be continuous (only use plugs with ground pins; no missing ground pin). 2.No Reversing Polarity - No grounded conductor can be attached to any terminal reversing its designated polarity.
- Must Have General Disconnect – (Main Breaker) Must have a disconnect that allows all conductors to be disconnected from service entrance.
repair to extension cords
- Repairs to Extension Cords - can only be made to 12 gauge or larger extension cords.
- Repairs must maintain insulation - Repairs (splices) must maintain outer sheath insulation properties (No electrical tape).
- Strain relief - must be provided.
a low resistance path from a tool to the earth to disperse unwanted current.
grounding
energy flows through the ____ and NOT YOU!! … to the ground, protecting you from electrical shock, injury and death.
ground wire
Tools plugged into improperly grounded circuits may become ____.
Energized
Common OSHA Violation
Broken wire or plug on extension cord. Also called Grounding.
what are four grounding rules?
- Ground your equipment
- Inspect frequently
- Inspect before use
- Don’t remove ground prongs
What are the results of overloading circuits?
- Too many devices plugged in
- using damaged tools
- No over-current protection
- melting wire insulation
This situation can cause arcing and a fire in the area where the overload exists, …even inside a wall
Overloading circuits
They Automatically open circuit if unsafe current is detected – they “shut off” electricity
Electric Circuit Protective Devices
Fuses do what?
melt
Circuit breakers do what?
trip
GFIs do what?
Isolate the load
GFCI cuts electricity off___.
off in 1/40th of a second if a ground fault is detected.
on all 120volt, single-phase, 15- and 20ampere receptacles, or have an assured equipment grounding conductor program.
A GFI should be used
are designed to cut off a flow of electricity if a current “leakage” is detected in an electrical circuit.
GFCI’s
are designed to trip at 4-6 milliamps (painful shock level).
Tripping GFCI’s
required on temporary 120v 15-20 amp outlets – (not part of permanent wiring system).
GFCI’s
not required on permanent power – (unless tool used with extension cord).
GFCI
- GFCI monitors - the amount of current
flowing from “hot” to “neutral”. - GFCI trips the circuit - If it detects an imbalance as small as 5 milliamps ,… and it can react as quickly as 1/30 th of a second .
- GFCI rendered useless - Never snip off the “ground” prong on a plug ; that will negate the safety feature a GFCI provides.
How a GFI works
Joe’s outside with his power drill and it’s raining. Joe’s standing on the ground , and since his drill is wet … there is a path from the hot wire inside the drill through Joe to ground. If electricity flows from hot to ground through Joe, it could kill him. The GFCI senses the current flowing through Joe
because not all of the current is flowing from hot to neutral as it expects – some of it is flowing through Joe to ground… THERE IS A ‘CURRENT’ LEAK!! As soon as the GFCI senses that, _______.
it trips the circuit and cuts off the electricity
GFCI protection is required on all portable generators _____ or greater.
5kW (5,000 watts)
GFCI protection can be built in or added as a ___.
Pig tail
Specific WRITTEN procedures adopted by the employer.
Assured Equipment Grounding Program (AEGP)
All cord sets, receptacles and any equipment connected by cord shall be inspected before each day’s use.
Procedures for (AEGP)
Assured Grounding written program, ____.
Must be kept on site, and implemented by competent person.
What is the coverage for assured grounding?
equipment (connected by plug & cord), all cords, plugs, receptacles (not part of a building or structure), & power tools.
Assured grounding should be tested …..
(1) before 1st use, (2) at least every 3 mo., (3) after service, & (4) after possible damage.
Assured grounding test Records kept ….
by color coding, other means, & by written log.
Must Be Inspected - Equipment must be
(1) inspected before installation & (2) suitable for the intended use. Use per Manufacturer’s Instructions - Listed, labeled, and certified equipment to be used per manufacturer’s instructions. Label all Breakers - All circuit breakers must be labeled.
Electrical equipment
Access to live parts 50+ volts must be Controlled by either…
restricted areas or physical locations.
Electrical equipment must be…..
protected
Electrical rooms must be…
marked
must use _____ devices designed for that purpose (wire nuts) or by brazing, welding, or soldering.
splicing
Electrical equipment must not be used unless the manufacture’s name, trademark and other markings giving voltage, current, wattage, etc. are ___.
legible
…Cannot be used for Storage
…Must have Access and “Elbow Room” - Sufficient access and working space must be provided and maintained around all electrical equipment.
…Work-Space Clearances - Minimum working clearances per Table K-1. 3 ft2 – In front of the elec. Equip. (in the direction of access to the live
working spaces
Controls on equipment during service/repair with clear identification must be…..
Lockout/Tag out
Circuits or equipment that are de-energized must be locked & tagged to prevent unauthorized ____ at any point.
re-energizing
Lockout/Tag out of Circuits requires what?
- Apply locks to power source after de-energizing
- Tag (de-activated) controls
- Tag (de-energized) equipment and circuits at all points where they can be energized
- Tags must identify equipment or circuits being worked on
Use barriers/guards - Pre-plan work - post warnings & use protective measures Keep work areas clear - of cords, debris, trip hazard
Protect workers from electric shock
Don’t use worn or frayed cords Don’t fasten with staples Don’t hang from nails Don’t suspend objects with them
cord safety
Plan your work with others Plan to lock-out/tag-out equipment Remove jewelry Avoid wet conditions Avoid overhead power lines
safe work practices
train employees to ____.
- De-energize before starting to work 2. Use only cords, tools, etc that are in good repair 3.Lockout/Tag out procedures
- Use PPE Proper Protective Equipment
Inadequate wiring Exposed electrical parts Bad insulation on wiring Ungrounded tools, elec. systems Overloaded circuits Damaged power tools, equip. Wrong PPE, tools Overhead power lines Wet conditions make all hazards worse
hazards
Proper grounding Use GFCI’s Use fuses & circuit breakers Guard live parts Lockout/Tag out Proper use of flexible cords Close electric panels Train
protective measures
At what amperage will a GFCI trip?
4 - 6 milliamps
What is the proper way to repair an extension cord?
Repair only 12 gauge or larger; Repair must maintain insulation properties – shrink sleeve?
What should we do to protect unauthorized employees from entering electrical rooms with live parts?
Mark the room with Warning Signs forbidding entrance by unqualified, unauthorized person
What type(s) of electrical cords are acceptable for use in construction?
3 - wire type & hard or extra hard duty
