Highlights: ■ Identification of Conductors

■ New Machines and Additions to Existing Buildings

■ Grounding Portable Tools and Equipment

■ Oil and Electricity

■ Electrical Safety Checklist

Electrical Maintenance of Fixtures and Circuits

Nearly 300 work-related deaths each year are attributed to electrocution. That represents five percent of all workplace fatalities. Properly maintaining electrical wiring and equipment is essential to preventing fires and electrical incidents.

Not only do you need to check wires and cords, you also need to look at the wiring configuration of your building or area. Any addition of new equipment or facility expansion can create an unsafe electrical condition that was perfectly safe before.

Consider the following when examining your facility’s electrical maintenance:

■ Code requirements

■ Proper fusing

■ Identification of conductors

■ Grounding machines

■ New machines and additions to existing buildings

■ Extension cords

■ Grounding portable tools and equipment

Code RequirementsThe National Electric Code (NFPA 70) was established specifically to set standards for safe wiring installation, be it new or from updates and changes. A licensed electrician will know your code requirements.

Proper FusingOverfusing is a dangerous practice and a frequent cause of electrical fires. Overfusing is most often found in older buildings with older electrical wiring and service. The size of wire used in a branch circuit determines the load that can be connected safely. The proper size fuse or circuit breaker will help prevent overheating or burnout by limiting the amount of current flow.

Ordinarily, on circuits of 14 AWG (American Wire Gauge) wire, 15 ampere fuses should be used; on circuits of 12 gauge wire, 20 amperes is the proper fuse size. “Fusestats” (a suggested means of preventing tampering and overfusing) or “fusetrons” (for individual motor protection) will help prevent motor failure from overloads as well as protect the rest of the circuit from accidental shutdown.

As a rule, the maximum current each wire size can safely conduct is shown, but your situation will demand that the selection be matched with material of conductor (copper or aluminum), temperature rating, insulation factor, dimensional design length of service, and single vs. three-phase systems. Refer also to table 310.16 NEC2008, pages 70-148.

Wire size Maximum Current

14 AWG 15 amps

12 AWG (stranded) 20 amps

12 AWG (solid) 20 amps

10 AWG 30 amps

8 AWG 40 amps

6 AWG 55 amps

2 AWG 95 amps

1/0 AWG 125 amps

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Conductor IdentificationEquipment and grounding conductors of an electrical circuit must be marked or color-coded in such a way that allows employees to identify them and tell them apart from the other conductors in the circuit.

The grounded conductor is an energized circuit conductor that is connected to the earth through the system ground. It is commonly referred to as “neutral.” The equipment grounding conductor is not an energized conductor under normal conditions and acts as a safeguard against insulation failure or faults in the other circuit conductors. The equipment grounding conductor is energized only if there is a leak or fault in the normal current path and it directs this current back to the source. Doing so enables protective devices, such as circuit breakers or fuses to operate, thus, preventing fires and reducing the hazard of electrical shocks.

Clearly mark all outlets in the same building where more than one voltage is available through the outlet. Plugs and outlets must be configured to make it physically impossible to insert a 3-wire, 110 volt plug into a 220 volt circuit.

Grounding MachinesImproper grounding is one of the principal improper safety conditions cited by OSHA. Compliance with the National Electric Code is a must.

Grounding can be accomplished by connecting machine castings to a low resistance path, such as to driven ground rods or an extensive water system. A grounding wire is usually incorporated in a wiring circuit from the supply outlet. However, this is no proof that the machine is properly grounded. Have an electrician remove the covers on all outlet boxes to ensure the grounding wires are actually connected to something.

Machines with 3-phase motors must be grounded. In a 4-wire connection, one wire must connect the frame to a low resistance ground.

New Machines and Additions to Existing BuildingsBe sure to meet all code requirements when installing new equipment or adding on to your facility. If planning to add to an existing circuit, determine the wire size and present load to ensure this will not cause an overload. You may need to run a new branch circuit. When installing larger capacity equipment, or if the addition is extensive, check with the power supplier to make sure their facilities can accommodate the increased load. Seek professional guidance from a certified electrician if new machines and service demands are beyond the capabilities of your internal staff.

Extension CordsAs a general rule, by OSHA and NFPA definitions, extension cords are designed for temporary applications, not intended to replace long term sources of electrical conduit. Use the proper size and type extension cord to prevent an electrical overload from causing a fire. Extension cords should be of heavy rubber-cover construction with the socket and plug made of hard rubber. Ground fault circuit interrupters (GFCI) or low voltage systems should be used. Avoid tripping hazards and possible damage to the cords by placing them out of high traffic areas.

Grounding Portable Tools and EquipmentPortable electric tools, such as welders, drills, impact wrenches and hammers are potential sources of electrical injury. Make sure the tool wiring is polarized; meaning equipped with a specialized attachment plug so that it can only be connected one way and the case of the tool is always grounded. Use a 3-wire cord on single phase, or a 4-wire cord on 3-phase, with the odd wire as a ground wire. Check local or state codes for allowable grounding techniques or variances. Reversed polarity is a common cause

New outlet

Existing outlet

As a substitute for fixed wiring

Through walls, ceilings, floors, doors or windows

Where concealed

Where attached to building surface

Figure 1: Examples of prohibited uses of extension cords

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of a power tool’s electrical failure, with potentially severe consequences to the user when they become part of the tool’s current to ground.

If a ground fault occurs in a defective tool, the grounding conductor must carry enough current to immediately trip the circuit breaker or blow the fuse. This requires that the ground fault path have low impedance. Make sure all electrical power tools are listed by a nationally recognized testing laboratory, such as Underwriter’s Laboratory (UL). Inspect all tools and their cords before use and remove from service any with defects or exposed electrical wires. Provide continuity and insulation resistance testing (as well as polarity check) before placing repaired items back into service. It is especially important to take these precautions when a tool is used on a metal or possibly grounded object, or where the worker may be standing in a damp area.

Tools protected by an approved system of double insulation or equivalent, with proper distinctive markings, need not be grounded. Many often are, however, to provide additional protection if/when the insulation is broken or where there may be contact with water or moisture.

Before use, inspect all portable electric tools and extension cords for external defects (loose parts, deformed or missing pins, or damaged outer insulation) and for evidence of internal damage (pinched or crushed insulation). Cord and plug-connected equipment and extension cords that remain connected once they are put into place, still need a visual inspection until they are relocated.

When the attachment plug is to be connected to a receptacle (including a cord set), check the relationship on the plug and receptacle contacts to ensure they are of the proper mating configuration. All extension cords that are used with grounding-type tools must contain an equipment grounding conductor. These attachment plugs and receptacles must not be connected or altered in any way that would prevent proper continuity of the equipment grounding conductor.

Internal Faults in Equipment WiringFigure 2 shows the correct wiring for the common 120-volt outlet with a portable hand tool attached.

20-Amp Circuit Breaker

Figure 2

120-volt branch circuit with black and white wires reversed.Suppose now that the black (ungrounded) and white (grounded conductors) are reversed as shown in Figure 3. This is reversed polarity. Although a shock hazard may not exist, there are other mechanical hazards that can occur.

20-Amp Circuit Breaker

Figure 3

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If an internal fault should occur in the wiring, as shown in Figure 4, the equipment would

not stop when the switch is released, or it would start as soon as a person plugs the supply cord into the improperly wired outlet. This could result in serious injury.

20-Amp Circuit Breaker

Figure 4

White and green wires reversed.Figure 5 shows the white (grounded) and green (grounding) conductors reversed. Although it is not fitting, considering OSHA or code terminology to call this reversed polarity, a hazard can still exist. In this case, due to the wiring error, the white wire is being used to provide equipment grounding. Under certain conditions, this could be dangerous.

20-Amp Circuit Breaker

Figure 5

Black and green wires reversed.Figure 6 shows an extremely dangerous situation. The black (ungrounded) and green (grounding) conductors have been reversed. The metal case of the equipment is at 120 volts with reference to the surroundings. As soon as a person picks up the equipment and touches a conductive surface in their surroundings, they will receive a serious, possibly deadly shock.

20-Amp Circuit Breaker

Figure 6

Housekeeping and Electrical EquipmentIt is important to maintain a regular schedule of cleaning and maintaining electrical equipment. Accumulation of dust and dirt on a motor housing, or sawdust, swarf and shavings around a motor not only increase the fire hazard but can contribute to premature equipment failure. It is equally important to have measures in place to prevent equipment misuse or abuse.

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Moisture and ElectricityWhen working in tanks, boilers and other damp places, make every effort to keep electrical equipment dry. Make sure the cord is connected to the 6 volt side of a 110/6 volt transformer and use a 6 volt lamp constructed of moisture-proof wire and non-metallic shell sockets with lamp guards.

Oil and ElectricityWhen lubricating machinery, over-oiling can be just as hazardous as under-oiling. Excessive oil can soak into motor windings and hasten insulation deterioration, and the accumulation of dust, dirt and lint create a fire hazard. Clean up excess oil and properly discard cleaning rags and materials.

If oil switches or oil circuit breakers are used to control or protect motor circuits, regular preventive maintenance is vital to reduce the potential for fire or explosion.

Finally, be certain that all such machine upkeep is done when power is disabled and machine movement comes to a complete and controlled stop. Verify that there is no residual pressure or kinetic energy and follow your lockout/tagout plan.

Entrance and Access to Electrical EquipmentAt least one entrance, not less than 24 inches wide and 6 feet 6 inches high, is necessary to give access to the working space near electric service equipment. Switchboard and control panels exceeding 48 inches wide must have one entrance at each end. Where bare energized parts of any voltage (or insulated energized parts above 600 volts) are located near this entrance, suitable guarding or shielding must be provided. Refer to NFPA 70E for information on suitable personal protective equipment, boundary protection to the magnitude of risk, and work practices to minimize arc flash or arc blast risk.

FansMake sure that fan blades have proper guarding attached. Place fans so that nothing can be drawn into them, such as clothing or hair. Avoid accidental contact from people or objects by mounting fans above head level, unless they are physically inaccessible to workers or patrons. Do not locate fans near walkways or aisles or where passersby can easily be at risk.

Use substantial mounting supports to prevent vibration. Should excessive vibration develop, brace the fan or remove it from service until it can be re-balanced.

Portable fans should be equipped with a 3-wire cord for grounding purposes. Before putting a portable fan into service, thoroughly inspect it for damage, giving particular attention to the cord. Make sure the connection to the fan motor is solid, with no wire ends that can energize the motor frame.

All fans need frequent lubrication. Be sure that the unit is shut off or that power has been disconnected before proceeding with maintenance.

SummaryA good maintenance program for electrical equipment not only reduces the risk of fire, explosion and personal injury, it can also save your company from repair costs, premature replacements and downtime.

Follow these best safety practices for your workplace:

■ Develop a preventive and predictive maintenance schedule—and stick to it.

■ Maintain good housekeeping practices, including proper disposal of cleaning materials.

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■ Upgrade old or outdated fixtures and wiring to conform to current energy demands and operations.

■ Follow all National Electrical Code standards. When in doubt, seek the advice of a licensed electrician.

ReferencesNational Electrical Code (NFPA 70), Arc Flash (NFPA 70E) and Electrical Safety for Machines (NFPA 79).

Occupational Safety and Health Administration (OSHA) 1910.330-.333 Electrical Safety Related Work Practices, and 1926.404 Wiring Design and Protection.

Electrical Safety; Safety and Health for Electrical Trades—A Student Manual, National Institute for Occupational Safety and Health (NIOSH) and Centers for Disease Control (CDC), Publication No. 2002-123, Cincinnati, OH, January 2002.

Liberty Mutual Insurance Risk Control Reference Note, RC 5415, Arc Flash Precautions.

Liberty Mutual Insurance Risk Control Reference Note, RC 5425, Working on Energized Electrical Circuits.

Electrical Safety ChecklistThis checklist references some conditions and practices that appear to account for a significant portion of electrical injuries or damage. Use it to help direct your electrical safety evaluations. It is not intended to be all-inclusive as there may be areas unique to your operations that are not listed.

Check your local, state and federal safety codes, the National Electric Safety Code and National Electric Code for additional information.

Management

Yes No NA1. Specify compliance with NEC (NFPA 70) for all electrical work.

2. Multi-plug adapters are prohibited.

3. The location of electrical power lines and cables (overhead, underground, sub-floor, opposite wall) is determined before drilling, digging, etc.

4. Metal measuring tapes, ropes, handlines or similar devices with woven metallic thread are prohibited from use where they could contact live energized parts.

5. Metal ladders are prohibited in areas where the ladder/user could encounter live energized parts.

6. Employees with regular access to energized electrical equipment are trained in CPR.

7. Employees utilize the “buddy system” when working on energized lines or equipment over 600 volts.

Inspections

Yes No NA1. Each motor is located in sight of its operator and

the controlling disconnection means is capable of being locked out in the OFF position.

2. All employees are instructed to make preliminary inspections and/or tests to verify safe conditions before starting electrical work.

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3. All employees are required to report obvious electrical hazards (of life or property).

4. Ground fault circuit interrupters (GFCI’s) are installed on each temporary 15-20 amp, 120 volt AC at locations where construction, demolition, modifications or excavations are underway.

5. If electrical installations are in hazardous locations with dust or vapors, they meet the NEC code (NFPA 70) for hazardous locations.

6. Exposed wiring and cords with frayed or deteriorated insulation are required to be replaced promptly.

7. Electrical tools and equipment used in wet or damp locations is appropriate for use, or otherwise protected.

8. All disconnecting means and circuit breakers have labels next to the appropriate area indicating their use and/or the equipment they serve.

9. Electrical raceways and enclosures are securely fastened in place.

10. Approved cabinets or enclosures are used to guard against accidental contact with energized parts of circuits or electrical equipment.

11. Unused openings in electrical enclosures and fittings are closed with appropriate covers, plugs or plates.

12. Electrical enclosures (switches, receptacles, junction boxes) have tight fitting covers or plates.

13. Disconnecting switches or electrical motors (greater than 2 horsepower) are capable of opening the circuit, without exploding, when the motor has stalled. Switches must have horsepower rating greater than or equal to the rating of the motor.

14. Motor-disconnecting switches or circuit breakers are located within sight of the motor control device.

Maintenance

Yes No NA1. When electrical equipment or lines need servicing,

maintenance, setup or adjustment, necessary switches are opened, locked out and tagged, whenever possible, and verified in a “zero energy state.”

2. Disconnection means are always opened before fuses are replaced.

3. Sufficient access and working space is provided and maintained around all electrical equipment to allow for safe operation and maintenance.

Grounding Circuits and Equipment

Yes No NA1. Portable electric tools and equipment is

grounded or effectively double insulated.2. Electrical appliances (i.e., vending machines, laundry

equipment, cleaners, etc.) are properly electrically grounded; no cheater plugs are used.

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3. Extension cords are equipped with a third grounding conductor and prong.

4. All interior wiring systems include provisions for grounding metal parts of electrical raceways, equipment and enclosures.

Temporary Wiring and Fixtures

Yes No NA1. Temporary circuits are protected by suitable disconnecting

switches or plug connectors, with permanent wiring at the junction.2. Flexible cords and cables are free from splices, tape or defects.

3. Flexible cords are used only for temporary means, and capable of handling the appropriate electrical flow (amperage) for the demand.

4. Clamps or other securing means are provided on flexible cords or cables at plugs, receptacles, etc., and the cord jacket is securely held in place.

5. All cord, cable and raceway connections are intact and secure.

6. Spark-producing devices are prohibited from use in hazardous atmospheres where volatile processes are performed.

7. Extension cord use does not exceed 60 days for most applications (e.g., shop floor machine use).

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