Electrical Safety

Electrical Safety

New England

Roofing Industry

Partnership

Training Objectives After completing this unit, you will:

– Be familiar with the fundamental concepts of electricity.

– Understand the potential effects of electricity on the human body.

– Be able to recognize common electrical hazards.

– Be familiar with electrical protective devices.

– Be knowledgeable about safe work practices.

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References

29 CFR 1926.400; Subpart K National Electric Code (NEC)

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2Electrical Safety

Take Electricity Seriously

Electricity is the second leading cause of death in construction.

Electrocutions make up 12% of construction fatalities annually.

Over 30,000 non-fatal shocks occur each year.

Over 600 deaths occur annually due to electrocution.


Electrical Accidents

Leading Causes of Electrical Accidents:– Drilling and cutting through cables– Using defective tools, cables and equipment– Failure to maintain clearance distances– Failure to de-energize circuits and follow

Lockout/Tagout procedures– Failure to guard live parts from accidental worker

contact– Unqualified personnel working with electricity– Improper installation/use of temporary electrical

systems and equipment– By-passing electrical protective devices


Harmful Effects of Electricity Shock – Most common and possibly

causing electrocution or muscle contraction leading to secondary injury

Burns – Resistance causes heat Fires – Enough heat or spark can

ignite combustible materials Explosions – Electrical spark can

ignite vapors in air


Fundamentals of Electricity

Voltage (E)– electrical pressure (water pressure)

Amperage (I)– electrical flow rate (gallons per minute)

Resistance (R)– restriction to electrical flow (pipe friction)


Fundamentals of Electricity

Electrical current is the flow of electrons through a conductor.

A conductor is a material that allows electrons to flow through it.

An insulator resists the flow of electrons.

Resistance opposes electron flow.


Current Flows in a Loop or Circuit

Circuits are AC (alternating current) or DC (direct current).

Current is usually AC.

AC current has five parts:

(1) Electrical source(2) HOT wire to the tool.(3) The tool itself(4) NEUTRAL wire returns

electricity from the tool(5) GROUND


How Shocks Occur

Current travels in closed circuits through conductors (water, metal, the human body).

Shock occurs when the body becomes a part of circuit.

Current enters one point & leaves at another.


Shocks Occur in Three Ways

Contact with both conductors

Contact with one conductor and ground

With a tool: contact with “hot” metal part and ground (1), (2) & (3)


Severity of the Shock

Severity of the Shock depends on:

– Amount of current • Determined by voltage and resistance to flow

– Path through the body– Duration of flow through the body– Other factors such as general health and

individual differences.


He sweats - and he dies...Luling, La. - A man was electrocuted when his sweat dripped into the electric drill he was using to build a swing set in his backyard, the coroner said.

Richard Miller was pronounced dead Sunday at St. Charles Hospital, said David Vial, St. Charles Parish coroner. Miller, 54, had been using an electric drill in 90 degree heat, Vial said Monday.

“Apparently the man was sweating profusely,” Vial said. “He probably was pushing against the drill with his chest and his perspiration went into the drill itself and made a contact.”

The Associated Press.


Controlling Electrical Hazards

Employers must follow the OSHA Electrical Standards (Subpart K)

Subpart K includes four proactive methods:– Electrical Isolation– Equipment Grounding– Circuit Interruption– Safe Work Practices


Electrical Isolation We can be safe by keeping electricity

away from us. We can:

– Insulate the conductors.• Example: The insulation on extension cords.

– Elevate the conductors.• Example: Overhead powerlines.

– Guard the conductors by enclosing them.• Example: Receptacle covers, boxes, &

conduit.


Insulating the Conductors The first way to safeguard workers from

electrically energized wires is through insulation.

Rubber and plastic is put on wires to prevent shock, fires, and short circuits.

It is always necessary to check the insulation on equipment and cords before plugging them in.

Remember, even the smallest defect will allow leakage!



This cord was hard-usage, but has been worn out.

Defective Extension Cords

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Defective Cord Incident

Attempting to climb scaffold with electric drill.

Drill’s cord was worn open.

The wire contacted the scaffolding.

The worker died!


Elevating the Conductors The second way to safeguard workers from

electrically energized wires is by elevating them.

Wires are often elevated by the power company.

It is always necessary to check the location of overhead lines before you begin work and throughout the day.

Remember, never allow yourself, your tools, or the materials you are working with be within 10 feet of energized lines!


Working Near Overhead Lines Clearance of worker and any equipment,

tool, material, or scaffold near uninsulated lines

– Less than 50 kv = 10 feet.– More than 50 kv = 10 feet + 0.4 inches for

each 1 kv

Clearance near insulated lines– Less than 300 volts = 3 feet.– 300 - 50 kv = 10 feet.


Working Near Overhead Lines

Cranes, Derricks, Hoists

– 50 kv or less = minimum distance is 10 feet.

– Over 50 kv = 10 feet + 0.4 for each kv over.

– In transit; no load = 4 foot minimum up to 50 kv.

– In transit; no load = 10 foot minimum if > 50 kv.


Overhead Line Incident Two workers

were attempting to remove a metal pole.

Pole made contact with 7200 volts.

One worker died.


Guarding the Conductors The third way to safeguard workers from

electrically energized wires is guarding them.

Covers, boxes, and enclosures are often put around conductors to prevent worker contact.

It is always necessary to check that electrical boxes and panels are covered and free from missing “knock-outs”.

Remember, electric equipment operating at 50 volts more must be guarded!



Equipment Grounding

We can be safe by providing a separate, low resistance pathway for electricity when it does not follow normal flow.

Grounding gives the stray current somewhere to go and keeps you from becoming part of the circuit.


Can You Rely on Grounding?

Grounding will not work if the electricity can flow through you more easily than the ground. This can happen when:

– Your tool doesn’t have a ground pin.– You’re working in water.– You’re touching a metal object.


What Must be Grounded?

All circuits and extension cords. All noncurrent carrying metal parts. Portable & semi-portable tools and

equipment unless double insulated. Exemption for portable generators if

less than 5 kV. No grounding by-pass devices!



Do Not Eliminate the Ground!

You become the next-best path for current!


Do Not Reverse Polarity

The prongs are different sized so you can’t turnthe plug around. If youdo, the electrical fieldswithin the motor are alwaysenergized. If there ismoisture present, the case is likely to be “hot”. Evenwith double-insulated tool, you still could get a shock.

Circuit Interruption We can be safer by automatically shutting

off the flow electricity in the event of leakage, overload, or short circuit.

Fuses, circuit breakers, & Ground Fault Circuit Interrupters (GFCI) are circuit protection (or “overcurrent”) devices.

Remember, circuit breakers & fuses protect equipment, not you, because they take too much current & too much time to trip.

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Circuit Protective Devices Circuit Breakers and Fuses

– Only protect the building, equipment, and tools from heat build-up!

– Never depend on circuit breakers or fuses to prevent shocks!

Ground Fault Circuit Interrupter (GFCI)– Is the only device which will protect the

worker from shock and electrocution!


GFCI vs. Circuit Breaker Shock Protection


15 AMP Circuit Breaker Blows

4.000 AMP – burns, heart paralysis

0.100 AMP – certain heart failure, fatal

0.050 AMP – possible heart failure

0.030 AMP – temporary lung paralysis

0.015 AMP – can’t let go of power

0.005 AMP GFCI Opens

0.003 AMP – painful shcok

0.001 AMP – mild shock

GFCI Protection

All temporary circuits are required to have GFCI protection or:– Equipment & cords must be included

in an Assured Equipment Grounding Conductor Program

An extension cord is a temporary circuit (attach GFCI to front, not end of cord).

Types: receptacle, circuit breaker and portable

Must be wired correctly and tested.


How a GFCI Works

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The GFCI detects‘leakage’ of 4-6milliamps & opensthe circuit in 1/40th

of a second.

It will work withoutthe ground plugbut not fastest enough if you are The ground .

Types of GFCI Protection

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GFCI Testers

Assured Equipment Grounding Conductor Program

Requires the following:

– Written program and specific procedures

– Program implemented by a Competent Person

– Equipment grounding conductors must be tested (tools, extension cords, and circuits):

• At least every three months for cords & tools• At least every six months for receptacles• Results recorded - equipment coded (colored

tape)


Checking for Ground Continuity

What else we should we notice here?

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Temporary Wiring

There must be separate circuits for electric tools and lighting, each labeled as such.

Light circuits do not require a GFCI.– Unless used in a wet location.

Test branch circuits before use. Maintain vertical clearances. Insulate wires from their supports.

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Electrical Safety

Permanent Equipment in Temporary Use

What is wrong with using this as a ‘splitter’?

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Extension Cords and Cables Must be in good shape without splices. Cannot be secured with staples, nails or

bare wire. Must be protected from damage. Must have a ground pin. Should be inspected regularly and pulled

from service if defective. OSHA permits only 3-wire extension

cords designed for hard or extra hard usage (NEC 400).


Acceptable Cord Types

OSHA requires cords to meet the National Electric Code’s (NEC) Table 400-4 hard usage or extra hard usage ratings.

Look for markings stamped on cords. Acceptable Cord Types

– Extra Hard Use Markings: S, ST, SO, STO

– Hard Usage Markings: SJ, SJO, SJT, SJTO


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Extension Cords-What’s the Difference?

Clever? Or Foolish?

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Temporary Lighting

All bulbs must be guarded

No broken bulbs or empty sockets

Not suspended by conductors

Low voltage for wet locations


Portable Generators The frame of the

portable generator need not be grounded if:– the generator supplies

only cord and plug connected equipment.

– The non-current carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.

– GFCI is required if >5kV

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Safe Work Practices

Before work begins, employer must must determine where exposed and concealed energized circuits are located.

Once found, warning signs must be posted.

Workers need to know the location, hazards, and protective measures.


Safe Work Practices Person in charge determines if

performance of work could bring contact with energy.

– Distance of the worker to the energy source should be considered first.

– Tools, materials, and processes should also be considered to see if they could potentially shorten the safe separation distance.

• Examples: Metal Flashing, Re-bar, Bull-floats, etc.


Safe Work Practices

Must not permit work near electric circuit unless the worker is protected by:– De-energizing the circuit and grounding it.– Guarding it effectively by insulation.– Other means (maintaining safe separation)

De-energized circuits and equipment must be locked/tagged out.


Safe Work Practices No metal ladders for or near electrical

work. No wet hands when plugging or

unplugging. No raising or lowering tools by the

cords. Unless equipment designed for,

cannot be used in damp and wet locations, or in extremely hot or chemically destructive work environments.


Electrical Safety(1926.400 - .449)


Common OSHA Citations:– .404(b)(1)(i): Branch circuits: GFCI

protection/Assured Equipment Grounding Conductor Program

– .404(f)(6): Grounding path– .403(b)(2): Equipment installation and use– .404(b)(1)(ii): GFCI– .403(i)(2)(i): Guarding live parts

How can the hazards addressed by these Standards best be corrected, controlled, or eliminated?

Review Questions True or False?

1.Shocks and Electrocutions are the most common type of electrical accident and are the fourth leading cause of worker deaths.

2.The human body will not conduct electricity.

3. It takes at least 1 amp going through a worker to kill them.

4. Insulation on extension cords, elevated power lines, and receptacle box covers are examples of protection through isolation.



5.All portable and semi-portable tools and equipment must be grounded unless double insulated.

6.You, your tools, and the materials you are working with, must never be closer than 3 feet of energized power lines!

7.Electric equipment operating at 50 volts more must be guarded!

8.All circuits and extension cords must be grounded.



9. Circuit breakers and fuses are designed to protect the worker from electrocution.

10. GFCI protection or Assured Ground Continuity is required of all temporary circuits.

11. Extension cords are not required to have a ground prong when they are GFCI-protected.

12. It is OK to work on a circuit which has not been de-energized.


Documents

Electrical Safety