Key definitions for general industry and construction

• Key terms are defined in this section.

Labeled: Equipment is labeled if there is attached to it a label, symbol, or other identifying mark of a nationally recognized testing laboratory: (1) That makes periodic inspections of the production of such equipment, and (2) Whose labeling indicates compliance with nationally recognized standards or tests to determine safe use in a specified manner.

Listed: Equipment is listed if it is of a kind mentioned in a list that: (1) Is published by a nationally recognized laboratory that makes periodic inspection of the production of such equipment, and (2) States that such equipment meets nationally recognized standards or has been tested and found safe for use in a specified manner.

Qualified person: A qualified person is someone who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved. Whether an employee is considered a “qualified person” will depend upon various circumstances in the workplace. For example, it is possible and, in fact, likely for an individual to be considered qualified with regard to certain equipment in the workplace, but unqualified as to other equipment. (See 1910.332(b)(3) for training requirements that specifically apply to qualified persons.) An employee who is undergoing on-the-job training and who, in the course of such training, has demonstrated an ability to perform duties safely at their level of training and who is under the direct supervision of a qualified person is considered a qualified person for the performance of those duties.

Readily accessible: Something that is capable of being reached quickly for operation, renewal, or inspections, so that those needing ready access do not have to climb over or remove obstacles or to resort to portable ladders, chairs, etc.

Electrical safety for general industry

• OSHA standards for electrical safety are found in 1910.302-1910.399.
• OSHA’s electrical requirements apply to all workers exposed to electrical hazards at work.

Electrical accidents at work may be caused by one or more of the following: Unsafe equipment and/or installation; unsafe workplaces caused by environmental factors; and unsafe work practices.

The Occupational Safety and Health Administration (OSHA) standards are covered in 1910.302 through 1910.399 (Subpart S) — Electrical. Sections 1910.302 through 1910.308 contain design safety standards for electric utilization systems. Included in this category are all electric equipment and installations used to provide electric power and light for employee workplaces. Sections 1910.331 through 1910.335 include training and employee safeguards. Section 1910.399 contains definitions.

OSHA’s electrical requirements generally apply to all workers who are exposed to the particular hazard subject to the requirement. The requirements vary, depending on training, voltages, type of work and equipment, and other factors.

What is covered by the standards?

The general industry electrical standards cover electrical installations and utilization equipment installed or used within or on buildings, structures, and other premises, including:

• Yards,
• Carnivals,
• Parking and other lots,
• Mobile homes,
• Recreational vehicles,
• Industrial substations,
• Conductors that connect the installations to a supply of electricity, and
• Other outside conductors on the premises.

What is not covered by the standards?

The general industry electrical standards do not cover:

• Installations in ships, watercraft, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles;
• Installations underground in mines;
• Installations of railways for generation, transformation, transmission, or distribution of power used exclusively for operation of rolling stock or installations used exclusively for signaling and communication purposes;
• Installations of communication equipment under the exclusive control of communication utilities, located outdoors or in building spaces used exclusively for such installations; or
• Installations under the exclusive control of electric utilities for the purpose of communication or metering; or for the generation, control, transformation, transmission, and distribution of electric energy located in buildings used exclusively by utilities for such purposes or located outdoors on property owned or leased by the utility or on public highways, streets, roads, etc., or outdoors by established rights on private property.

Approved electrical conductors and equipment

Electrical conductors and equipment used by the employer must be approved.

Approved in the general industry regulations (1910 Subpart S) means sanctioned, endorsed, accredited, certified, or accepted as satisfactory by a duly constituted and nationally recognized authority or agency.

Electrical safety for the construction industry

Electricity has long been recognized as a serious workplace hazard, exposing employees to dangers like electric shock, electrocution, fires, and explosions.

OSHA’s construction electrical requirements apply to all workers who are exposed to electrical hazards. Depending on training, voltages, type of work and equipment, and other factors, the requirements vary.

What are the regulations?

Section 1926 Subpart K is divided into five parts:

• Section 1926.402 through 1926.408 — Installation safety requirements. Included in this category are electric equipment and installations used to provide electric power and light on jobsites.
• Section 1926.416 and 1926.417 — Safety-related work practices. In addition to covering the hazards arising from the use of electricity at jobsites, these regulations also cover the hazards arising from the accidental contact, direct or indirect, by employees with all energized lines, above or below ground, passing through or near the jobsite.
• Section 1926.431 and 1926.432 — Safety-related maintenance and environmental considerations.
• Section 1926.441 — Safety requirements for special equipment.
• Section 1926.449 — Definitions.

What types of electrical equipment must be used?

• Electrical equipment should be free from recognized hazards and suitable for installation — listed and labeled, for example, with an Underwriters Laboratories (UL) certification.
• Electrical equipment must be installed and used according to manufacturers’ instructions.

When looking for electrical equipment, employers should make sure that it is listed and labeled by a nationally recognized testing laboratory (NRTL) and that it is installed as the manufacturer intended. In addition, the equipment must be marked with the manufacturer’s name or trademark, voltage, current, wattage, and other necessary information.

NRTLs are third-party, private sector organizations recognized by the Occupational Safety and Health Administration (OSHA) as having the technical capability to perform safety testing and certification of particular types of products. NRTLs provide testing and certification services to the manufacturers of a wide range of products used in the workplace.

Employers may expose workers to serious hazards when they use a non-approved (e.g., job-built), counterfeit, improperly approved, or modified products instead of an NRTL-approved product as required by an OSHA standard. NRTL approval ensures that a product meets applicable test-standard requirements and will operate safely in the workplace.

For example, NRTL approval ensures that an electric product will operate at its rated voltage, current and power, and will not exceed limits that pose hazards to workers. These hazards include electric shock, arc flash, blast events, electrocution, equipment shorts, explosions, burns, fires, toxic atmospheres generated by burning and decomposing insulation and other materials associated with electrical fires, and wiring and component failures.

One example of the relationship between OSHA standards, NRTLs and suitable electrical equipment can be found in an OSHA Letter of Interpretation (LOI) dated November 18, 2002. This LOI discusses the use of power strips (also known as surge/spike protectors or portable outlets), features of which typically include multiple electrical receptables, an on/off switch, circuit breaker, and a grounded flexible power cord. The LOI notes that one NRTL, Underwriters Laboratories (UL), refers to such devices as relocatable power taps (RPTs).

OSHA’s standard requires electrical equipment such as RPTs to “be installed and used in accordance with any instructions included in the listing or labeling,” and notes that manufacturers and NRTLs determine the proper uses for such equipment. For example, UL requires that any UL-listed RPTs must be directly connected to permanently installed branch circuit receptables, must not be series-connected to other RPTs, and must not be connected to extension cords.

The LOI further discusses the correct use of RPTs in regard to power loads, noting that per OSHA standards, such devices are appropriate to be used with low-powered load equipment like computers, peripherals, or audio-visual equipment, but not suitable for high-powered loads such as refrigerators and microwaves. It also discusses proper handling of the RPT’s flexible power cord, which is not to be routed through walls, windows, ceilings, floors, or similar openings, in accordance with 1910.305(g)(1).

What criteria determine the need for electrical safety training?

• Employees who face a risk of electric shock at work should be trained in safe work practices around electricity.

The provisions of these standards cover electrical safety-related work practices for both qualified persons (those who have training in avoiding the electrical hazards of working on or near exposed energized parts) and unqualified persons (those with little or no such training) who are working on, near, or with the following installations:

• Premises wiring — Installations of electric conductors and equipment within or on buildings or other structures, and on other premises such as yards, carnival, parking, and other lots, and industrial substations;
• Wiring for connections to supply — Installations of conductors that connect to the supply of electricity; and
• Other wiring — Installations of other outside conductors on the premises.

Who must receive electrical safety training?

The training requirements apply to employees who face a risk of electric shock that is not reduced to a safe level by the electric installation requirements of 1910.3031–1910.308. Employees in occupations listed below face such risk and are required to be trained:

Except for electricians and welders, workers in the above groups do not need to be trained if their work or the work of those they supervise does not bring them or the employees they supervise close enough to exposed parts of electric circuits operating at 50 volts or more to ground for a hazard to exist. Other employees who also may reasonably be expected to face a comparable risk of injury due to electric shock or other electrical hazards must also be trained.

Spacing and grounding requirements for electrical equipment

• Sufficient access and workspace must be provided around all electrical equipment.
• GCFIs shut off electricity when a current leakage is detected, which can prevent electrocution, but not all risk of electric shock.
• Assured equipment grounding programs require regular inspection and testing of certain electrical equipment.

How much space must be maintained around electrical equipment?

Employers are required to provide and maintain sufficient access and working space around all electric equipment. A certain amount of space is needed to operate the equipment and to perform any needed maintenance. The electrical equipment must be readily accessible.

Depending on the voltage and the condition (e.g., exposed wiring) the minimum clear distance needed in front of the panel is 3 feet. The width of working space in front must be the width of the equipment or 30 inches, whichever is greater. In addition, the working space must allow a 90-degree opening of equipment doors or hinged panels.

Refer to Table S-1 for the minimum depth of clear working space for 600 volts or less and Table S-2 for over 600 volts.

The workspace must be clear and not used for storage. If indoors, it must extend from the grade, floor, or platform to a height 6 feet above the equipment or to the structural ceiling, whichever is lower. Necessary control equipment is permitted in the dedicated space.

Is ground-fault circuit interrupter protection needed?

The ground-fault circuit interrupter (GFCI) is a fast-acting device which senses small current leakage to ground and, in a fraction of a second, shuts off the electricity and interrupts its faulty flow to ground. The rapid response of the GFCI is fast enough to prevent electrocution and this protection is independent of the condition of the ground conductor.

A GFCI can prevent an electrocution; however, it cannot by itself prevent an electric shock to an employee before it interrupts the circuit. This initial shock could lead to injuries of an indirect or secondary nature in which involuntary muscular reaction could cause bruises, bone fractures, and even death resulting from collisions or falls. Therefore, GFCIs are in addition to, and not in lieu of, equipment grounding conductor requirements.

Is an assured equipment grounding program needed?

• Employers should implement an assured equipment grounding conductor program, which requires inspection and testing of cord sets, receptacles that are not a part of the building or structure, and equipment connected by cord and plug that are available for use or used by employees on those receptacles. This testing must be done every three months, except for cord sets and receptacles which are fixed and not exposed to damage, which should be tested at least every six months.

Temporary power and flexible cords/cables

• Temporary electrical power installations are allowed under limited circumstances.
• Flexible cords and cables may only be used under limited circumstances.

When is the use of temporary electrical power allowed?

Temporary electrical power and lighting installations of 600 volts, nominal, or less may be used only as follows:

• During and for remodeling, maintenance, or repair of buildings, structures, or equipment, and similar activities;
• For a period not to exceed 90 days for Christmas decorative lighting, carnivals, and similar purposes; and
• For experimental or development work, and during emergencies.

Temporary wiring shall be removed immediately upon completion of the project or purpose for which the wiring was installed.

Temporary electrical installations of more than 600 volts may be used only during periods of tests, experiments, emergencies, or construction-like activities.

When can flexible cords and cables be used?

Flexible cords and cables may only be used for:

• Pendants,
• Wiring of fixtures,
• Connection of portable lamps or appliances,
• Portable and mobile signs,
• Elevator cables,
• Wiring of cranes and hoists,
• Connection of stationary equipment to facilitate their frequent interchange,
• Prevention of the transmission of noise or vibration,
• Appliances where the fastening means and mechanical connections are designed to permit removal for maintenance and repair,
• Data processing cables approved as a part of the data processing system,
• Connection of moving parts, and
• Temporary wiring as permitted above.

Flexible cords and cables may not be used:

• As a substitute for the fixed wiring of a structure;
• Where they run through holes in walls, ceilings, or floors;
• Where they run through doorways, windows, or similar openings;
• Where they are attached to building surfaces;
• Where they are concealed behind building walls, ceilings, or floors; or
• Where they are installed in raceways.

What are the lockout/tagout requirements?

• Lockout/tagout procedures protect workers who are servicing equipment or machinery that has been temporarily de-energized.

While any employee is exposed to contact with parts of fixed electric equipment or circuits which have been de-energized, the circuits energizing the parts must be locked out or tagged or both in the following order:

• Procedures must be in place before equipment is de-energized.
• Circuits and equipment to be worked on must be disconnected from all electrical energy sources.
• Stored electrical energy which poses a hazard to workers must be released.
• Stored non-electrical energy in devices that could re-energize electric circuit parts must be blocked or relieved to the extent that the circuit parts could not be accidentally energized by the device.
• A lock and a tag must be placed on each disconnecting means used to de-energize circuits and equipment on which work is to be performed, except as provided below.
• Each tag shall contain a statement prohibiting unauthorized operation of the disconnecting means and removal of tag.
• If a lock cannot be applied, or if the employer can demonstrate that tagging procedures will provide a level of safety equivalent to that obtained by the use of a lock, a tag may be used without a lock.
• A tag used without a lock must be supplemented by at least one additional safety measure that provides a level of safety equivalent to that obtained by the use of a lock. Examples include the removal of an isolating circuit element, blocking of a controlling switch, or opening of an extra disconnecting device.
• A lock may be placed without a tag only under the following conditions: (a) Only one circuit or piece of equipment is de-energized, and (b) The lockout period does not extend beyond the work shift, and (c) Employees exposed to the hazards associated with re-energizing the circuit or equipment are familiar with this procedure.

How can employees be protected from electric shock and arc flash and blast?

• Protective equipment such as shields, barrier and insulating materials may be used to protect workers from electric shock and arc flash and blast.

The Occupational Safety and Health Administration (OSHA) requires employees to:

• Wear protective equipment for the eyes or face wherever there is danger of injury to the eyes or face from electric arcs or flashes or from flying objects resulting from electrical explosion.
• Use protective shields, protective barriers, or insulating materials to protect themselves from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur. When normally enclosed live parts are exposed for maintenance or repair, they must be guarded to protect unqualified persons from contact with the live parts.

Installation safety requirements

• Electrical equipment must be approved, free from hazards, guarded when needed, and protected from overcurrent.

This applies to installations, both temporary and permanent, used on the jobsite; but they do not apply to existing permanent installations that were in place before the construction activity commenced.

Approved electrical conductors and equipment

The electrical conductors and equipment used by the employer must be approved.

Approved in the construction regulations (1926 Subpart K) means acceptable to the authority enforcing this Subpart. The authority enforcing this Subpart is the Assistant Secretary of Labor for Occupational Safety and Health.

What is required for examination, installation, and use of equipment?

The employer must ensure that electrical equipment is free from recognized hazards that are likely to cause death or serious physical harm to employees. Safety of equipment must be determined by:

• Suitability for installation and use in conformity with the provisions of the standard. Suitability of equipment for an identified purpose may be evidenced by listing, labeling, or certification for that identified purpose.
• Mechanical strength and durability, including, for parts designed to enclose and protect other equipment, the adequacy of the protection provided.
• Electrical insulation.
• Heating effects under conditions of use.
• Arcing effects.
• Classification by type, size, voltage, current capacity, and specific use.
• Other factors which contribute to the practical safeguarding of employees who use or are likely to come in contact with the equipment.

What types of guarding are required?

Live parts of electric equipment operating at 50 volts or more must be guarded against accidental contact. Guarding of live parts must be accomplished by any of the following means:

• Location in a cabinet, room, vault, or similar enclosure accessible only to qualified persons.
• Use of permanent, substantial partitions or screens to exclude unqualified persons.
• Location on a suitable balcony, gallery, or platform elevated and arranged to exclude unqualified persons.
• Elevation of 8 feet or more above the floor.

Entrance to rooms and other guarded locations containing exposed live parts must be marked with conspicuous warning signs forbidding unqualified persons to enter. Electric installations that are over 600 volts and that are open to unqualified persons must be made with metal-enclosed equipment or enclosed in a vault or area controlled by a lock. In addition, equipment must be marked with appropriate caution signs.

What is overcurrent protection?

The following requirements apply to overcurrent protection of circuits rated 600 volts, nominal, or less:

• Conductors and equipment must be protected from overcurrent in accordance with their ability to safely conduct current and the conductors must have sufficient current carrying capacity to carry the load.
• Overcurrent devices must not interrupt the continuity of the grounded conductor unless all conductors of the circuit are opened simultaneously, except for motor-running overload protection.
• Overcurrent devices must be readily accessible and not located where they could create an employee safety hazard by being exposed to physical damage or located in the vicinity of easily ignitable material.
• Fuses and circuit breakers must be so located or shielded that employees will not be burned or otherwise injured by their operation.

When should equipment connected by cord and plug be grounded?

Exposed noncurrent-carrying metal parts of cord- and plug-connected equipment which may become energized must be grounded if the equipment is:

• In a hazardous (classified) location.
• Operated at over 150 volts to ground, except for guarded motors and metal frames of electrically heated appliances if the appliance frames are permanently and effectively insulated from ground.
• One of the types listed below (Item 6 lists an exemption):
  1. Handheld motor-operated tools.
  2. Cord- and plug-connected equipment used in damp or wet locations or by employees standing on the ground or on metal floors or working inside metal tanks or boilers.
  3. Portable and mobile x-ray and associated equipment.
  4. Tools likely to be used in wet and/or conductive locations.
  5. Portable hand lamps.
  6. (Exemption) Tools likely to be used in wet and/or conductive locations need not be grounded if supplied through an isolating transformer with an ungrounded secondary of not over 50 volts. Listed or labeled portable tools and appliances protected by a system of double insulation, or its equivalent, need not be grounded. If such a system is employed, the equipment must be distinctively marked to indicate that the tool or appliance uses a system of double insulation.

What are the safety-related work practices?

• Employees must be protected from various hazards associated with electricity in the workplace.
• Some methods of protection include guarding, distance, protective equipment, tools in good working order, and good training/judgment.

The employer must not permit an employee to work near any part of an electric power circuit that the employee could contact in the course of work, unless the employee is protected against shock by de-energizing the circuit and grounding it or by guarding it effectively by insulation or other means.

Good safety related work practices include the use of:

Protective equipment. Employees whose occupations require them to work directly with electricity must use the personal protective equipment required for the jobs they perform. This equipment may consist of rubber insulating gloves, hoods, sleeves, matting, blankets, line hose, and industrial protective helmets.

Tools. To maximize safety, an employee should always use tools that work properly. Tools must be inspected before use, and those found questionable should be removed from service and properly tagged. Tools and other equipment should be regularly maintained. Inadequate maintenance can cause equipment to deteriorate, resulting in an unsafe condition. Tools that are used by employees to handle energized conductors must be designed and constructed to withstand the voltages and stresses to which they are exposed.

Good judgment. Perhaps the single most successful defense against electrical accidents is the continuous exercising of good judgment or common sense. All employees should be thoroughly familiar with the safety procedures for their particular jobs. When work is performed on electrical equipment, for example, some basic procedures are:

• Have the equipment de-energized.
• Ensure that the equipment remains de-energized by using some type of lockout and tag procedure.
• Use insulating protective equipment.
• Keep a safe distance from energized parts.

How are employees protected against underground electric powerlines?

When the exact location of underground electric powerlines is unknown, employees using jack hammers or hand tools which may contact a line must be provided with insulated protective gloves. Before work is begun, the employer must determine by inquiry, observation, or instruments where any part of an exposed or concealed energized electric power circuit is located. This is necessary because a person, tool or machine could come into physical or electrical contact with the electric power circuit. The employer is required to advise employees of the location of such lines, the hazards involved, and protective measures to be taken as well as to post and maintain proper warning signs.

How are employees protected at passageways and open spaces?

The employer must provide barriers or other means of guarding to ensure that workspace for electrical equipment will not be used as a passageway during the time when energized parts of electrical equipment are exposed. Walkways and similar working spaces must be kept clear of electric cords. Other standards cover load ratings, fuses, cords, and cables.

What are the requirements for lockout and tagging of circuits?

Tags must be placed on controls that are to be deactivated during the course of work on energized or de-energized equipment or circuits. Equipment or circuits that are de-energized must be rendered inoperative and have tags attached at all points where such equipment or circuits can be energized.

What are the requirements for working near overhead powerlines?

If work is to be performed near overhead power lines, the lines must be de-energized and grounded by the owner or operator of the lines, or other protective measures must be provided before work is started. Protective measures (such as guarding or insulating the lines) must be designed to prevent employees from contacting the lines.

Unqualified employees and mechanical equipment must stay at least 10 feet away from overhead power lines. If the voltage is more than 50,000 volts, the clearance must be increased by 4 inches for each additional 10,000 volts.

When mechanical equipment is being operated near overhead lines, employees standing on the ground may not contact the equipment unless it is located so that the required clearance cannot be violated even at the maximum reach of the equipment.

Safety-related maintenance and environmental considerations

• Environmental conditions, such as damp areas or excessive temperatures, can lead to deterioration of electrical equipment.
• Batteries must be properly stored in a ventilated area where surfaces will not be damaged by acids and fumes.
• Flexible cords, which are often part of construction power tools, pose specific hazards and must be used and maintained properly.

Construction jobsites often change on a weekly, if not daily, basis. That’s why it’s so important to maintain electrical equipment in order to protect all the trades working there. In addition, changing environmental conditions can jeopardize worker safety.

What is the proper way to maintain equipment?

The employer must ensure that all wiring components and utilization equipment in hazardous locations are maintained in a dust-tight, dust-ignition-proof, or explosion-proof condition without loose or missing screws, gaskets, threaded connections, seals, or other impairments to a tight condition.

How can you prevent environmental deterioration of equipment?

Unless identified for use in the operating environment, no conductors or equipment can be located:

• In damp or wet locations.
• Where exposed to gases, fumes, vapors, liquids, or other agents having a deteriorating effect on the conductors or equipment.
• Where exposed to excessive temperatures.

Control equipment, utilization equipment, and busways approved for use in dry locations only must be protected against damage from the weather during building construction. For protection against corrosion, metal raceways, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware must be made of materials appropriate for the environment in which they are installed.

What are the safety requirements for batteries?

• Batteries of the unsealed type must be located in enclosures with outside vents or in well-ventilated rooms arranged to prevent the escape of fumes, gases, or electrolyte spray into other areas. Other provisions include:
• Ventilation — to ensure diffusion of the gases from the battery and to prevent the accumulation of an explosive mixture.
• Racks and trays — treated to make them resistant to the electrolyte.
• Floors — acid resistant construction unless protected from acid accumulations.
• Face shields, aprons, and rubber gloves — for workers handling acids or batteries.
• Facilities for quick drenching of the eyes and body — within 25 feet (7.62 m) of battery handling areas.
• Facilities — for flushing and neutralizing spilled electrolytes and for fire protection.

What are the hazards of flexible cords?

With the wide use of portable tools on construction sites, the use of flexible cords often becomes necessary. Hazards are created when cords, cord connectors, receptacles, and cord- and plug-connected equipment are improperly used and maintained.

Generally, flexible cords are more vulnerable to damage than is fixed wiring. Flexible cords must be connected to devices and to fittings so as to prevent tension at joints and terminal screws. Because a cord is exposed, flexible, and unsecured, joints and terminals become more vulnerable. Flexible cord conductors are finely stranded for flexibility, but the strands of one conductor may loosen from under terminal screws and touch another conductor, especially if the cord is subjected to stress or strain.

A flexible cord may be damaged by activities on the job, by door or window edges, by staples or fastenings, by abrasion from adjacent materials, or simply by aging. If the electrical conductors become exposed, there is a danger of shocks, burns, or fire. A frequent hazard on a construction site is a cord assembly with improperly connected terminals.

When a cord connector is wet, hazardous leakage can occur to the equipment grounding conductor and to humans who pick up that connector if they also provide a path to ground. Such leakage is not limited to the face of the connector but also develops at any wetted portion of it.

When the leakage current of tools is below 1 ampere, and the grounding conductor has a low resistance, no shock should be perceived. However, should the resistance of the equipment grounding conductor increase, the current through the body also will increase. Thus, if the resistance of the equipment grounding conductor is significantly greater than 1 ohm, tools with even small leakages become hazardous.

What is ground-fault protection?

• Insulation and grounding are two common means of ground-fault protection.

Ground-fault protection of equipment (GFPE) is defined in the National Electrical Code (NEC) [1] in Article 100.

Insulation and grounding are two recognized means of preventing injury during electrical equipment operation. Conductor insulation may be provided by placing nonconductive material such as plastic around the conductor. Grounding may be achieved through the use of a direct connection to a known ground such as a metal cold water pipe.

Consider, for example, the metal housing or enclosure around a motor or the metal box in which electrical switches, circuit breakers, and controls are placed. Such enclosures protect the equipment from dirt and moisture and prevent accidental contact with exposed wiring.

However, there is a hazard associated with housings and enclosures. A malfunction within the equipment — such as deteriorated insulation — may create an electrical shock hazard. Many metal enclosures are connected to a ground to eliminate the hazard. If a “hot” wire contacts a grounded enclosure, a ground fault results which normally will trip a circuit breaker or blow a fuse.

Metal enclosures and containers are usually grounded by connecting them with a wire going to ground.

This wire is called an equipment grounding conductor. Most portable electric tools and appliances are grounded by this means. There is one disadvantage to grounding: a break in the grounding system may occur without the user’s knowledge.

Insulation may be damaged by hard usage on the job or simply by aging. If this damage causes the conductors to become exposed, the hazards of shocks, burns, and fire will exist. Double insulation may be used as additional protection on the live parts of a tool, but double insulation does not provide protection against defective cords and plugs or against heavy moisture conditions.

The use of a ground-fault circuit interrupter (GFCI) is one method used to overcome grounding and insulation deficiencies.

What is a GFCI?

A GFCI is a fast-acting circuit breaker which senses small imbalances in the circuit caused by current leakage to ground and, in a fraction of a second, shuts off the electricity. The GFCI continually matches the amount of current going to an electrical device against the amount of current returning from the device along the electrical path. Whenever the amount “going” differs from the amount “returning” by approximately 5 milliamps, the GFCI interrupts the electric power within as little as 1/40 of a second (see diagram).

However, the GFCI will not protect the employee from line-to-line contact hazards (such as a person holding two “hot” wires or a hot and a neutral wire in each hand). It does provide protection against the most common form of electrical shock hazard — the ground fault. It also provides protection against fires, overheating, and destruction of insulation on wiring.

GFCIs can be used successfully to reduce electrical hazards on construction sites. Tripping of GFCIs — interruption of current flow — is sometimes caused by wet connectors and tools. It is good practice to limit exposure of connectors and tools to excessive moisture by using watertight or sealable connectors. Providing more GFCIs or shorter circuits can prevent tripping caused by the cumulative leakage from several tools or by leakages from extremely long circuits.

What is the employer’s responsibility for ground-fault protection?

• OSHA requires ground-fault protection either through GFCIs or an assured equipment grounding conductor program.

The Occupational Safety and Health Administration (OSHA)’s ground-fault protection rules and regulations have been determined necessary and appropriate for employee safety and health. Therefore, it is the employer’s responsibility to provide either:

• Ground-fault circuit interrupters (GFCIs) on construction sites for receptacle outlets in use and not part of the permanent wiring of the building or structure; or
• A scheduled and recorded assured equipment grounding conductor program on construction sites, covering all cord sets, receptacles which are not part of the permanent wiring of the building or structure, and equipment connected by cord and plug which are available for use or used by employees.

When should employers provide GFCIs?

The employer is required to provide ground-fault circuit interrupters for all 120-volt, single phase, 15- and 20 -ampere receptacle outlets on construction sites which are not a part of the permanent wiring of the building or structure and which are in use by employees. Receptacles on the ends of extension cords are not part of the permanent wiring and, therefore, must be protected by GFCIs whether or not the extension cord is plugged into permanent wiring.

These GFCIs monitor the current-to-the-load for leakage to ground. When this leakage exceeds 5 mA plus or minus 1 mA, the GFCI interrupts the current. They are rated to trip quickly enough to prevent electrocution. This protection is required in addition to, not as a substitute for, the grounding requirements of OSHA’s safety and health rules and regulations (1926).

The requirements which the employer must meet when using the GFCI option are stated in 1926.404(b)(1)(ii).

When should employers use an assured equipment grounding conductor program?

An assured equipment grounding conductor program covers all cord sets, receptacles which are not a part of the permanent wiring of the building or structure, and equipment connected by cord and plug which are available for use or used by employees. The requirements which the program must meet are stated in 1926.404(b)(1)(iii), but employers may provide additional tests or procedures.

OSHA requires that a written description of the employer’s assured equipment grounding conductor program, including the specific procedures adopted, be kept at the jobsite. This program should outline the employer’s specific procedures for the required equipment inspections, tests, and test schedule.

The required tests must be recorded. This record must be kept by means of logs, color coding, or other effective means and must be maintained until replaced by a more current record. The written program description and the recorded tests must be made available, at the jobsite , to OSHA and to any affected employee upon request. The employer is required to designate one or more competent persons to implement the program.

Electrical equipment noted in the assured equipment grounding conductor program must be visually inspected for damage or defects before each day’s use. Any damaged or defective equipment must not be used by the employee until repaired.

Two tests are required by OSHA. One is a continuity test to ensure that the equipment grounding conductor is electrically continuous. It must be performed on all cord sets, receptacles which are not part of the permanent wiring of the building or structure, and on cord- and plug-connected equipment which are required to be grounded. This test may be performed using a simple continuity tester, such as a lamp and battery, a bell and battery, an ohmmeter, or a receptacle tester.

The other test must be performed on receptacles and plugs to ensure that the equipment grounding conductor is connected to its proper terminal. This test can be performed with the same equipment used in the first test.

These tests are required before first use, after any repairs, after damage is suspected to have occurred, and at three-month intervals. Cord sets and receptacles which are essentially fixed and not exposed to damage must be tested at six-month intervals. Any equipment which fails to pass the required tests shall not be made available for or used by employees.

How should employers control electrical hazards?

• Employers may protect employees from electrical hazards through safe work practices, insulation, guarding, grounding, and circuit protection devices.

In general, the Occupational Safety and Health Administration (OSHA)’s electrical standards are based on the National Fire Protection Association (NFPA)’s Standard NFPA 70E, Electrical Safety Requirements for Employee Workplaces, and in turn, from the National Electrical Code (NEC).

OSHA also has electrical standards for construction (Part 1926 Subpart K — equivalent to those in Subpart S but with fewer safety-related work practices) but recommends that employers in this industry follow the general industry electrical standards whenever possible for hazards that are not addressed by their industry-specific standards.

Electrical accidents appear to be caused by a combination of three possible factors: unsafe equipment and/or installation, workplaces made unsafe by the environment, and unsafe work practices. There are various ways of protecting people from the hazards caused by electricity. Besides simply using safe work practices, safety measures may include insulation, guarding, grounding, circuit protective devices, and safe work practices.

Safe work practices

Employees and others working with electric equipment need to use safe work practices. These include: deenergizing electric equipment before inspecting or making repairs, using electric tools that are in good repair, using good judgment when working near energized lines, and using appropriate protective equipment. Electrical safety-related work practice requirements are contained in Subpart S of 1910, 1910.331-1910.335.

What are the training requirements?

• Employers in the construction industry are required to train workers to recognize and protect against electrical hazards in the workplace.

The Occupational Safety and Health Administration (OSHA)’s training requirement at 1926.21(b)(2) requires employers to train construction employees to recognize and avoid unsafe conditions, and to understand regulations that apply to the work environment that are designed to control or eliminate exposure to injury or illness hazards.

To ensure that they use safe work practices, employees must be aware of the electrical hazards to which they will be exposed. Employees must be trained in safety-related work practices as well as any other procedures necessary for safety from electrical hazards.

The accidental or unexpected sudden starting of electrical equipment can cause severe injury or death. Before any inspections or repairs are made — even on the so-called low-voltage circuits — the current must be turned off at the switch box and the switch padlocked in the OFF position. At the same time, the switch or controls of the machine or other equipment being locked out of service must be securely tagged to show which equipment or circuits are being worked on.

Maintenance employees must be instructed in lockout procedures. No two locks should be alike; each key should fit only one lock, and only one key should be issued to each maintenance employee. If more than one employee is repairing a piece of equipment, each should lock out the switch with their own lock and never permit anyone else to remove it. The maintenance worker should always avoid exposing other employees to danger.

Insulation

• Insulation protects workers by covering energized wires and parts with materials that have a high resistance to electrical current.

One way to safeguard individuals from electrically energized wires and parts is through insulation. An insulator is any material with high resistance to electric current.

Insulators — such as glass, mica, rubber, and plastic — are put on conductors to prevent shock, fires, and short circuits. Before employees prepare to work with electric equipment, it is always a good idea for them to check the insulation before making a connection to a power source to be sure there are no exposed wires. The insulation of flexible cords, such as extension cords, is particularly vulnerable to damage.

Conductors and cables are marked by the manufacturer to show the maximum voltage and American Wire Gage size, the type letter of the insulation, and the manufacturer’s name or trademark. Insulation is often color coded. In general, insulated wires used as equipment grounding conductors are either continuous green or green with yellow stripes. The grounded conductors that complete a circuit are generally covered with continuous white or natural gray-colored insulation. The ungrounded conductors, or “hot wires,” may be any color other than green, white, or gray. They are often colored black or red.

Guarding

• Guarding prevents unqualified persons from accessing areas of live electricity, though location, barriers, and signage.

Live parts of electric equipment operating at 50 volts or more must be guarded against accidental contact. Guarding of live parts may be accomplished by either:

• Location in a room, vault, or similar enclosure accessible only to qualified persons.
• Use of permanent, substantial partitions or screens to exclude unqualified persons.
• Location on a suitable balcony, gallery, or platform elevated and arranged to exclude unqualified persons; or
• Elevation of 8 feet or more above the floor.

Entrances to rooms and other guarded locations containing exposed live parts must be marked with conspicuous warning signs forbidding unqualified persons to enter.

Indoor electric wiring more than 600 volts and that is open to unqualified persons must be made with metal-enclosed equipment or enclosed in a vault or area controlled by a lock. In addition, equipment must be marked with appropriate caution signs.

Grounding

• Grounding provides a low-resistance path for electricity to reach the earth without causing a hazard to workers; it cannot, however, prevent all risk of shock.

Grounding is another method of protecting employees from electric shock; however, it is normally a secondary protective measure. The term “ground” refers to a conductive body, usually the earth, and means a conductive connection, whether intentional or accidental, by which an electric circuit or equipment is connected to earth or the ground plane.

By grounding a tool or electrical system, a low-resistance path to the earth is intentionally created. When properly done, this path offers sufficiently low resistance and has sufficient current carrying capacity to prevent the buildup of voltages that may result in a personnel hazard. This does not guarantee that no one will receive a shock, be injured, or be killed. It will, however, substantially reduce the possibility of such accidents, especially when used in combination with other safety measures discussed in this section.

There are two kinds of grounds required by Design Safety Standards for Electrical Systems (Subpart S). One of these is called the “service or system ground.” In this instance, one wire — called “the neutral conductor” or “grounded conductor” — is grounded. In an ordinary low-voltage circuit, the white (or gray) wire is grounded at the generator or transformer and again at the service entrance of the building. This type of ground is primarily designed to protect machines, tools, and insulation against damage.

To offer enhanced protection to the workers themselves, an additional ground, called the “equipment ground,” must be furnished by providing another path from the tool or machine through which the current can flow to the ground. This additional ground safeguards the electric equipment operator if a malfunction causes the metal frame of the tool to become accidentally energized. The resulting heavy surge of current will then activate the circuit protection devices and open the circuit.

Circuit protection devices

• Circuit protection devices like GFCIs protect workers by automatically shutting off the flow of electricity when an improper current is detected.

Circuit protection devices are designed to automatically limit or shut off the flow of electricity in the event of a ground-fault, overload, or short circuit in the wiring system. Fuses, circuit breakers, and ground-fault circuit interrupters are three well-known examples of such devices.

Fuses and circuit breakers are over-current devices that are placed in circuits to monitor the amount of current that the circuit will carry. They automatically open or break the circuit when the amount of current flow becomes excessive and therefore unsafe. Fuses are designed to melt when too much current flows through them. Circuit breakers, on the other hand, are designed to trip open the circuit by electro-mechanical means.

Fuses and circuit breakers are intended primarily for the protection of conductors and equipment. They prevent over-heating of wires and components that might otherwise create hazards for operators. They also open the circuit under certain hazardous ground-fault conditions.

The ground-fault circuit interrupter (GFCI) is designed to shut off electric power within as little as 1/40 of a second. It works by comparing the amount of current going to electric equipment against the amount of current returning from the equipment along the circuit conductors. If the current difference exceeds 6 milliamperes, the GFCI interrupts the current quickly enough to prevent electrocution. The GFCI is used in high-risk areas such as wet locations and construction sites.