When cranes and derrick operations are conducted around power lines, the employer must determine if any part of the equipment, load line or load (including rigging and lifting accessories), if operated up to the equipment's maximum working radius in the work zone, could get closer than 20 feet to a power line. If so, the employer must meet one of the following requirements:
Voltage (nominal, kV, alternating current) | Minimum clearance distance (feet) | |
---|---|---|
Up to 50 | 10 | |
Over 50 to 200 | 15 | |
Over 200 to 350 | 20 | |
Over 350 to 500 | 25 | |
Over 500 to 750 | 35 | |
Over 750 to 1000 | 45 | |
Over 1000 | (As established by the power line owner/operator or registered professional engineer who is a qualified person with respect to electrical power transmission and distribution) |
The following are preventive measures for workers to consider. Before work begins, make sure:
Click the button below to a video on a crane contact electrical accident.
1. What is the minimum clearance distance from a power line rated at to 7.5 kV?
a. 5 feetCranes and other high-reaching equipment. Be sure the utility company has confirmed the voltage and, therefore, the safe working distance from the power lines. Also, if applicable and feasible, use a/an: observer; insulated link; boom cage guard; proximity device.
Mobile heavy equipment. If provided, use installed rider posts under power lines to avoid working too close to the power lines.
Scaffolds. Erecting scaffolds under or next to power lines may cause workers to violate safe clearance distances and expose them to electrocution. Care must be taken to ensure the scaffold does not contact power lines or that workers cannot expose themselves to electrocution while using equipment on the scaffold.
Ladders. Fatalities occur every year due to the use of metallic ladders under power lines. It's easy to forget the locations of power lines when focused on tasks. Therefore, use only nonconductive ladders and be sure to retract them before moving. If it's necessary to use metallic ladders, make sure you retract and carry them horizontally.
Material storage. Ensure no materials are stored under power lines, and use caution tape and signs to cordon off area under power lines.
Excavations. Locate and understand the markings the local underground line locator service has marked before digging. Hand dig within three feet of cable location (be aware that more than one underground cable may be buried in area of locator markings).
Let's take a look at a real world accident caused by failing to maintain safe clearance distances.
Description of Accident
Employees were moving a steel canopy structure using a crane. The boom cable made contact with a 7.2 kV electrical power distribution line electrocuting the operator of the crane; he was the foreman at the site.
Inspection Results
As a result of its investigation OSHA issued citations for four serious violations of its construction standards dealing with training, protective equipment, and working too close to power lines. OSHA's construction safety standards include several requirements that, if they had been followed here might have prevented this fatality.
What would you recommend?
Recommendations
2. Which of the following is necessary when using high-reaching equipment near overhead power lines?
a. Use metal/conductive laddersBefore working on overhead power lines, employers must ensure power lines are de-energized and grounded by the owner/operator of the lines, or other protective methods must be used, such as:
Employers must initially train workers upon initial assignment on specific safe work practices, safety procedures, and other safety requirements. Qualified employees must be trained in competent in:
Let's take a look at a real world accident caused by failing to maintain safe clearance distances.
Description of Accident
Five employees were constructing a chain link fence in front of a house and directly below a 7200-volt energized power line. They were installing 21-foot sections of metal top rail on the fence. One employee picked up a 21-foot section of top rail and held it up vertically. The top rail contacted the 7200-volt line, and the employee was electrocuted.
Inspection Results
Following its inspection, OSHA determined the employee who was killed had never received any safety training from his employer nor any specific instruction in avoiding the hazards posed by overhead power lines. The agency issued two serious citations for the training deficiencies.
What would you recommend?
Recommendations
3. Before working on overhead power lines, employees must use _____.
a. conductive shorting barsA GFCI is a ground fault circuit interrupter designed to protect people from severe and sometimes fatal electrical shock. A GFCI detects ground faults and interrupts the flow of electric current and is designed to protect the worker by limiting the duration of an electrical shock.
An Example of How a GFCI Works
A homeowner is using an old drill with a loose bare wire inside it touching the outer metal housing. When the drill is plugged in, the housing of the drill is charged with electricity. If it is used outside in the rain and the worker is standing on the ground, there is a path from the hot wire inside the drill through the worker to the ground. If electricity flows from the drill to ground through the worker, it could be fatal. GFCIs monitor the current-to-the load for leakage to ground. When this leakage exceeds 5 mA + 1 mA, the GFCI interrupts the current, trips the circuit, and cuts off the electricity.
Click the button to see a video explaining how GFCIs work.
Click the button below to review an accident caused improper GFCI safety.
Description of Accident
One employee was climbing a metal ladder to hand an electric drill to the journeyman installer on a scaffold about five feet above him. When the victim reached the third rung from the bottom of the ladder, he received an electric shock that killed him. The investigation revealed that the extension cord had a missing grounding prong and that a conductor on the green grounding wire was making intermittent contact with the energizing black wire thereby energizing the entire length of the grounding wire and the drill's frame. The drill was not double insulated.
Inspection Results
As a result of its investigation, OSHA issued citations for violations of construction standards.
What would you recommend?
Recommendations
4. A GFCI protects the worker by _____.
a. increasing the lag time for disconnectionReceptacle GFCI: Often found on construction work sites, outdoor areas and other locations where damp conditions do or could exist. The receptacle GFCI fits into the standard outlet box and protects users against ground faults when an electrical product is connected to the GFCI protected outlet.
These should be tested after installation and once a month by:
If a light or power tool remains "ON" when the "Test" button is pushed, the GFCI is not working properly or has been incorrectly installed (miswired). If this is the case, a qualified electrician needs to be contacted to properly wire or replace the GFCI device.
Portable/Temporary GFCI: A portable GFCI is an extension cord combined with a GFCI. It adds flexibility in using receptacles that are not protected by GFCIs. Extension cords with GFCI protection incorporated should be used when permanent protection is unavailable.
These should be tested prior to each and every use by:
5. Which devices should be tested at least once a month on a construction site?
a. All pneumatic toolsCircuit Breaker GFCI: The GFCI circuit breaker controls an entire circuit and is installed as a replacement for a circuit breaker on the main circuit board. Rather than install multiple GFCI outlets, one GFCI circuit breaker can protect the entire circuit. At sites equipped with circuit breakers, this type of GFCI might be installed in a panel box to give protection to selected circuits.
Circuit breaker GFCIs should be tested monthly. Keep in mind that the test will disconnect power to everything on the circuit.
OSHA ground-fault protection rules and regulations have been determined necessary and appropriate for worker safety and health. It is your employer's responsibility to provide either:
6. Which type of GFCI controls an entire electrical circuit?
a. Circuit breaker GFCIThe AEGCP covers all cord sets, receptacles that are not a part of the permanent wiring of the building or structure, and equipment connected by cord and plug that are available for use or used by employees. OSHA requires a written description of the employer's AEGCP, including the specific procedures adopted, be kept at the job site. This program should outline the employer's specific procedures for the required equipment inspections, tests, and test schedule.
The required tests must be recorded, and the record maintained until replaced by a more current record. The written program description and the recorded tests must be made available, at the job site, to OSHA and 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 AEGCP must be visually inspected for damage or defects before each day's use. The employee must not use any damaged or defective equipment until it is repaired.
OSHA requires two tests:
7. Which test is required by OSHA in the Assured Equipment Grounding Conductor Program (AEGCP)?
a. Secondary Connection TestThe OSHA construction standard requires flexible cords to be rated for hard or extra-hard usage. These ratings are derived from the National Electrical Code, and your employer is required to make sure the cord is indelibly marked approximately every foot along the length of the cord.
Workers need to inspect extension cords prior to their use for any cuts or abrasion. Extension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or appliance is damaged. When the insulation is damaged, exposed metal parts may become energized if a live wire inside touches them. Electric hand tools that are old, damaged, or misused may have damaged insulation inside. You can click the following links to review toolbox talk 2 and toolbox talk 3.
Flexible cords used with temporary and portable lights must be designed for hard or extra-hard usage. They must be marked with usage type designation size and number of conductors. The cord could be marked with a 14/3 meaning the conductor size (AWG) is 14, and the number of conductors is 3.
Extension cords must be 3-wire type so they may be grounded, and able to permit grounding of any tools or equipment connected to them.
Limit exposure of connectors and tools to excessive moisture by using watertight or sealable connectors.
In terms of conducting electrical current, size matters (the size of the electrical conductor). Click on the button below and look at the table regarding ampacity, the current-carrying capacity of a conductor in amps. You'll notice two things: the amount of current a wire can safely carry increases as the diameter (and area) of the wire increases and as the number of the wire size decreases.
AWG Copper Wire Table
Copper Wire Size (AWG) | Diameter(Mils) | Area (Circular mils) | Ampacity in Free Air | Ampacity as Part of 3-conductor Cable |
14 AWG | 64.1 | 4109 | 20 Amps | 15 Amps |
12 AWG | 80.8 | 6529 | 25 Amps | 20 Amps |
10 AWG | 101.9 | 10,384 | 40 Amps | 30 Amps |
8 AWG | 128.5 | 16,512 | 70 Amps | 50 Amps |
Click the buttons below to videos on a crane contact electrical cables and cords.
8. The cord marked as 14/3 means _____.
a. the conductor size is 14 and has 3 wiresWorkers using power tools and equipment should follow tool safety tips to avoid misusing equipment.
Click the buttons below to see some common examples of misusing equipment.
Workers need to know even when the power system is properly grounded, electrical equipment can instantly change from safe to hazardous because of extreme conditions and rough treatment.
What Must Your Employer do to Protect You?
Your employer needs to ensure all power tools and equipment are maintained in a safe condition to:
9. Using a 30-amp breaker in a system with 15 or 20 amp receptacles is not allowed because _____.
a. it does not engage until 20 volts is reachedLockout/tagout is an essential safety procedure to protect workers from injury while working on or near electrical circuits and equipment.
Lockout/tagout also prevents contact with operating equipment parts such as blades, gears, shafts, etc., and prevents the unexpected release of hazardous gases, fluids, or solid matter in areas where workers are present.
To protect against being electrocuted, workers need to follow lockout/tagout procedures. If performing lockout/tagout on circuits and equipment, you may use the following checklist.
Only qualified persons may work on electric circuit parts or equipment that has not been de-energized. Such persons must be capable of working safely on energized circuits and must be familiar with the proper use of special precautionary techniques, PPE, insulating and shielding materials, and insulated tools.
Let's take a look at a couple of a real world accident and a video about failures to follow lockout/tagout procedures.
Description of Accident
An electrician was removing metal fish tape (a fish tape is used to pull wire through a conduit run) from a hole at the base of a metal light pole. The fish tape became energized, electrocuting him.
Inspection Results
As a result of its inspection, OSHA issued a citation for three serious violations of the agency's construction standards. Had requirements for de-energizing energy sources been followed, the electrocution might have been prevented.
What would you recommend?
Recommendations
10. When using lockout/tagout of, be sure to identify _____.
a. voltage circuits above 120 vacIsolation.The employer must ensure electrical parts are properly isolated, and conductors entering boxes, cabinets, or fittings are protected from abrasion. Openings through which conductors enter must be closed. Unused openings in cabinets, boxes, and fittings must also be effectively.
All pull boxes, junction boxes, and fittings must have covers. Metal covers need to be grounded. In energized installations, each outlet box needs to have a cover, faceplate, or fixture canopy. Covers of outlet boxes having holes through which flexible cord pendants pass shall be provided with bushings designed for the purpose or shall have smooth, well-rounded surfaces on which the cords may rest.
Ensure Proper Guarding. Guarding involves locating or enclosing electrical equipment to ensure workers do not accidentally come into contact with its live parts. Effective guarding requires equipment with exposed parts operating at 50 volts or more to be placed where they are accessible only to authorized people qualified to work with/on the equipment.
Training. Workers need be trained in and familiar with the safety-related work practices that pertain to their respective job assignments. Employers should train their employees to:
11. What must your employer do to help protect you from electrical hazards?
a. Ensure electrical parts are properly isolatedRead the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.