Premium Membership ♕

Save 50% on all EEP Academy courses with Enterprise Membership Plan and study specialized LV/MV/HV technical articles & guides.

Home / Technical Articles / Six beautiful animals that cause interruptions and hazards to electric utilities

Problems & mitigation techniques

Animals are one the largest causes of customer interruptions for nearly every electric utility worldwide, right after human and other factors. Problems and mitigation techniques are as varied as the animals involved. Identifying and addressing physical root causes is often the most cost effective way to address reliability problems.

6 beautiful animals that may cause interruptions to electric utilities
6 beautiful animals that may cause interruptions to electric utilities

This technical article describes reliability concerns and common reliability improvement strategies for the following classes of animals:

  1. Squirrels,
  2. Mice, rats and gophers,
  3. Birds,
  4. Snakes,
  5. Fire ants, and
  6. Large animals (cattle, horses, bison, and bears).

1. Squirrels

Squirrels are extremely cute animals. Everybody love them, but unfortunately they are a reliability concern for all overhead distribution systems near wooded areas. Squirrels will not typically climb utility poles, but will leap onto them from nearby trees and cause faults by bridging grounded equipment with phase conductors.

Of the more than 365 species throughout the world, reliability concerns lie primarily with gray squirrels and red squirrels (see Table 1).

The gray squirrel, inhabiting most of the Northern Hemisphere, is the most common type of tree squirrel. Typical gray squirrels are fifteen inches long, weigh about one pound, and have bushy tails about as long as the combined head and body length. They have a typical diet of nuts, seeds, and fruit.

North American red squirrels (also known as pine squirrels and chickarees) are smaller then the gray (eight to ten inches in typical length), have fur that ranges from red to black, and have bushy tails about the same length as their body. Some subspecies can have red or black ear tufts and most have a white belly.

The red squirrel is found in coniferous forests, where it feeds on the seeds and cones of the pines, fir, and spruce trees.

Table 1 – Common types of squirrels and their typical maximum length

Squirrel TypeLocationLength
Eastern GrayEastern US, southern Canada20”
Western GreyWest Coast of US22”
FoxEastern US29”
North American RedAlaska, Canada, North US and West US12”

Squirrels are extremely agile, persistent and committed to travel routes that may include utility poles. Because of this, attempts to keep squirrels off of overhead utility equipment are usually futile and reliability improvement efforts should focus on equipment protection.

The most common technique is to install plastic animal guards on bushings and insulators to prevent squirrels from simultaneously touching the tank and phase conductors (Figure 1).

The figure to the left shows a squirrel causing a fault by bridging the phase voltage to the grounded transformer tank
Figure 1 – The figure to the left shows a squirrel causing a fault by bridging the phase voltage to the grounded transformer tank

The middle figure shows the bushing fitted with a plastic animal guard to prevent the squirrel from causing a fault. The right figure shows the bushing fitted with an electrostatic guard that deters an approaching squirrel with a harmless but noticeable electric shock.

Squirrel proofing electric transformers

Go back to Content Table ↑

2. Mice, Rats and Gophers

Mice, rats, and gophers are rodents that cause faults by gnawing through the insulation of underground cable. Rats and mice are the most common cause of animal related outages on underground equipment, and gophers are third (snakes are the second most common cause).

Besides chewing through insulation, mice and rats also create reliability problems by attracting snakes. To prevent these rodents from gaining access to underground equipment, all equipment cabinets and duct openings should be tightly sealed.

Some utilities have successfully used ultrasonic devices to ward off mice and rats.

An example of delivered ultrasonic animal protection device with HV equipment
Figure 2 – An example of delivered ultrasonic animal protection device with HV equipment (photo credit: INMR)

When gophers dig tunnels, they chew their way through any obstacle in their path, including electric cables and plastic conduit. Gophers are most common in the Midwestern US where they are often the most common cause of underground equipment failure.

Effective gopher control is difficult to achieve, with methods including traps, poisoned bait, poison gas, and ultrasonic techniques.

Premium Membership Required

This technical article/guide requires a Premium Membership. You can choose an annually based Plus, Pro, or Enterprise membership plan. Subscribe and enjoy studying specialized technical articles, online video courses, electrical engineering guides, and papers. With EEP’s premium membership, you get additional essence that enhances your knowledge and experience in low- medium- and high-voltage engineering fields.

Check out each plan’s benefits and choose the membership plan that works best for you or your organization.

Good To Know!Save 50% on all video courses by purchasing Enterprise plan.

Log In »Purchase »

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

  ⁄  one  =  2

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge