Written by Scott Young, President, Industrial Safety Institute
Having spent my career around high voltage equipment, I have seen some interesting events. Lightning striking the base of a steel substation structure roughly 60 feet away, 230 kV line losing an insulator due to sea fog and contamination, high voltage power lines sagging almost to the ground because of a forest fire underneath them, and so on.
People drive by power lines and never realize how much they depend on them, until the power goes off. These failures are sometimes the power company’s fault, but more often it is animals or the general public that cause the equipment to turn off. Most often it is a car hitting a pole, an animal making contact with a line, or a piece of industrial equipment making contact - a crane, roofing conveyor truck, concrete pumper, etc. - that cause the power to go off. I’ll come back to this subject in a minute.
The Federal Regulations require the power be turned off when possible. Many times this is difficult due to the power demands of our society. The following tips are intended to help increase general knowledge and raise your awareness when working in close proximity of high voltage power lines and equipment.
The general concept is that power lines do not move except on very windy days. That is not exactly true. The power lines that are higher off the ground - called sub-transmission or transmission lines - can and do move. Even the neighborhood power lines move some. "How is this possible?", you may ask. In simple terms it works like this: the lines are designed and installed in such a manner that allows them to expand or shrink depending on the weather conditions. In the winter the lines tend to stay tight unless ice and snow build up on them; the additional weight will then cause them to sag closer to the ground. Summer time has a similar effect for a different reason. The power lines will be somewhat straighter in the morning. As ambient temperature and the sun increase and more power is demanded in the early afternoon, the lines will sag, sometimes as much as seven feet. They can also move side to side between two to three feet. Very few people consider this when planning a job first thing in the morning mostly due to lack of understanding of power lines. This may have contributed to several accidents with power lines. This is the reason it is so important to keep at least the minimum distances required by the Federal Standards. I suggest more if one is not familiar with working around high voltage equipment.
The unique thing about power lines is their location and design. Looking up at a power line from the ground, the background is usually blue sky or clouds. Neither of these is conducive to getting an accurate base line for judging distance; additionally, the design of the wire can add optical illusion to the equation. These things make it very difficult, if not impossible to judge distance correctly. I know this because I have operated cranes and equipment in high voltages substation and close to power lines for many years. It is still difficult to judge exactly how far away the line is or how close it is no matter how good one's eyesight is.
Now let us get back to the power shutting off after heavy equipment has made contact. The power company has devices called relay protection that are designed to keep the power on or limit outage time. However, the relay device will turn the power line off immediately and stay off when the equipment is substantially grounded, i.e. connected to a power ground grid or a copper rod driven at least eight feet into the ground (remember to use your underground locator service). Equipment should also be connected/bolted with at least 2/0 copper cable for residential, or 4/0 copper cable for transmission voltages. This ground safety device will usually trip the relay and keep the power off if it has been installed correctly. If not, there is a risk of the relay turning the power back on as many as two more times (depends on regional settings) or the power staying on until manually turned off by the power company. This is the reason power lines sometimes keep the equipment energized for as long as 20 minutes. Grounding equipment is a requirement under Federal regulations 1926.1410(d) (11) when working closer than Table A zone. Depending on location, installing the grounding safety device may require using insulated tools as well.
In the event of a high voltage contact here are some tips to remember: when high voltage electricity flows through equipment or a crane during contact with a power line, the earth becomes energized in a circle around any area where the equipment or crane is making contact with the earth. The safest thing to do is stay on the equipment. The only reason to get off is if it catches fire. If this is the case, one should jump as far as possible from the equipment and shuffle or hop away from the equipment. Keep everyone clear of the equipment or crane during work around power lines. Do not use this equipment or crane after an event of this nature until it has been thoroughly inspected by a professional mechanic.
I hope this information helps clarify some of the technical aspects and the importance of being highly aware when working around high voltage equipment.
R. Scott Young BA, CUSP has worked in the power industry since 1978. He is a certified Substation Technician and a Circuit-breaker Technician. Scott owns Industrial Safety Institute and travels worldwide conducting electrical, technical and safety training programs. He has also conducted extensive audits for numerous private and government entities and utilities, and is an affiliated instructor for the University of South Florida OTI. ISI is based in Tampa, Florida www.IndustrialSafetyInstitute.com firstname.lastname@example.org Phone: 813-732-6445