Myth #1 – Electrical insulation can prevent you from being shocked

This is probably the most misunderstood and prevalent myth out there. We are probably all familiar with the properties of conductors and materials used for them. Materials such as gold, silver, aluminum, copper, and the ferrous metals are all excellent conductors of electricity. Most other materials around us have some resistance to electrical current flow of one degree or another.

Materials with a high resistance to electrical current are called insulators, or insulating material. Examples are plastic, rubber, fiberglass, wood, and glass. Materials manufactured and designed with electrical insulating qualities in mind, could have insulating properties measured in thousands of volts.

However, we need to understand that no material is effective at insulating someone from electrical current at any voltage. All dedicated insulators have a voltage limit to resisting electrical current flow. There is no insulating material that will protect you from a sufficiently high voltage. Remember, voltage is the pressure of the electron flow, and that pressure is exerted against the insulating material outwardly, as the electrical flow passes. Therefore, you will find that insulating materials have a voltage rating. The most common voltage rating for a electrical cords, power tools, and appliances is 600 V. Just as you can imagine what would happen if you put 6000 V on a 600 V cord. The same thing applies to any insulating material if a sufficiently high voltage is plied to it. Sometimes the only insulating protection is simply distance. (more…)

This is a four part series on the four leading causes of fatalities in the construction industry.  These four hazards, known as the Focus Four account for 8 to 9 out of every 10 fatalities in construction.  Today we’ll talk about the third leading fatality: electrocution hazards.

Electrocution hazards can be generalized into four categories: Working around power lines, working around power tools and extension cords, locking out and tagging out electrical equipment, and demolition work.
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20 is the New 10

OSHA has significantly changed it’s treatment of powerlines with its new subpart 1926.1407-1411.  In the past there was little to no discussion until personnel or equipment got within 10 feet of an overhead powerline.

Now, before assembly or disassembly of a crane, the employer must determine if it could come within 20 feet of a power line. If so, the employer must either confirm with the power company that the line is de-energized and visibly grounded at the worksite, make sure no part gets within 20 feet of the power line or follows Table A, which has minimum distances based on voltage.
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Certainly to the layman, medium voltage (601V to 2,000V) and high voltage (greater than 2,001V) work seems extremely dangerous, and in some cases that’s true. However, implementation of safe work practices, and improvements in safety equipment have made this work relatively safe. Many utility contractors employ stringent work rules which already comply with (and exceed) OSHA regulations. The following are highlights of some of the more important OSHA regulations for line work found under the “Power Transmission and Distribution” subpart of the Code of Federal Regulations.

Before any work can begin, OSHA requires a thorough assessment of the area to determine what parts are energized, the condition of poles, hardware, and equipment. This survey shall include any affected peripherals such as fire alarm, phone, or cable TV lines.

Workers then approaching a work area must maintain minimum clear distances from energized parts with a phase-to phase potential of 2,100 volts or higher. This applies to any workers who are not completely isolated, and includes workers using “hot sticks” or other similar devices that are insulated. For instance, the minimum clear distance for energized parts from 2,100 volts to 15,000 volts is 2 ft. This distance increases slightly to 2 ft. 4 in. for voltages from 15,001 volts to 35,000 volts, and increases incrementally thereafter.

Workers will first usually put on their personal protective equipment. OSHA does require that all rubber equipment and live-line tools be visually inspected prior to use. In addition, rubber gloves in particular shall be “air-tested” prior to use.

Lines and equipment that are deenergized to be worked on can, in most cases, visually show that it’s disconnected from energized portions of the system. In cases where an item is not visibly open or visibly locked out, special care needs to be taken.

First, the line needs to be identified and declared deenergized by a designated worker. All switches that can supply power to the deenergized section shall be plainly tagged that men are working on the section. If switches can be locked out, or have their handles removed (or other similar action) this shall be done to assure the switches cannot be turned on. After all the above work is performed, the section shall be final tested to verify the section is deenergized. At that point protective grounds shall be installed, and then work may start. When attaching ground leads, start by attaching the lead to the ground point, then connect the other end with insulating tools or similar devices. Reversal of the above process is performed when reenergizing the section.

OSHA has a few general regulations for equipment use. For instance, a visual inspection and test of brakes and operating systems shall performed on all equipment at the start of the workshift. Hydraulic fluids used in Aerial lifts or similar equipment shall be of the insulating type- with fire-resistant characteristics of this fluid being exempted for this type of high voltage work. Arial lifts used near energized lines or equipment are required to be either grounded or barricaded. Equipment (such as cranes) without a voltage rating shall be kept clear of high voltage lines and equipment by 10 ft. (for 50,000 volts and less). Also OSHA prohibits line work under adverse weather conditions (especially high winds) except during emergencies.

There are many regulations OSHA has for line-stringing operations, however most of these regulations are covered by normal company work rules. OSHA does, however, require a briefing to be held before work starts which discusses the following topics:

• The type of equipment to be used.
• The grounding devices and procedures to be used.
• The crossover methods to be used.
• The clearance authorization(s) required.

When stringing operations are parallel to existing, energized lines, a competent determination needs to be made to ascertain if dangerous, induced voltage buildups can occur, especially during switching and ground fault conditions. If this is the case, the entire stringing operations require grounding until conductor installation is complete. The normal OSHA regulations also apply as to inspecting all equipment and line stringing accessories, etc. prior to use.

Working on live-line bare-hand work is a specialty in itself. OSHA requires any worker attempting this type of work to be thoroughly training prior to working on any energized circuits. Before working on live-line bare-hand work, the following items need to be determined:

• The voltage rating of the circuit on which work will be performed.
• The clearances to ground or other phases on which work will be performed.
• The voltage limitations of the aerial-lift equipment to be used.

All equipment used for this type of work shall be designed, tested and intended for live-line bare-hand work. One of the keys to this work is the insulating capacity of the aerial bucket arm. The ability of the aerial bucket to be completely isolated from any other voltage potential make this type of live-line bare-hand work possible. Before the start of the workday, when higher voltages are worked during the day, or any other factors develop that may change voltage conditions, the aerial bucket arm shall be physically tested. This test consists of placing the bucket arm in contact for three minutes with the voltage to be encountered during the work. Leakage tests shall be made during the three minutes. If more than 1 microampere/ kilovolt rating (between phases) is found, the bucket arm fails the test and shall not be used until repairs are made.

Once the aerial lift passes the test, work may then proceed only with personal supervision by a person trained and qualified in live-line bare-hand work. Again, this may be standard procedure to those familiar with live-line work, but OSHA does require the conductive aerial bucket liner to be bonded to the energized line being worked before the line is worked on. The worker is also similarly bonded to the liner with conductive shoes, or leg clips. This ensures the worker (isolated from ground or other phases) is at exactly the same voltage potential as the line, thereby making the live line safe to perform work on.

A careful assessment of the applicable regulations should be reviewed with your own safety procedures to assure compliance with OSHA regulations.