I spend a lot of time inspecting electric supply facilities for hazardous conditions and violations of the National Electrical Safety Code® (NESC®). Even when I’m on vacation, I don’t stop inspecting. I’ve shared the “problems” with my wife so often that now she points them out to me. I’ve driven all over the United States and find that no matter where I go, the hazards are out there, particularly in non-utility owned supply facilities.
The most common hazard I see with substations is access by non-qualified persons. A substation (electric supply station) by definition is an area within which electric supply equipment is located and the interior of which is only accessible to qualified persons. Qualified persons are people having adequate knowledge of the installation, construction and operation of apparatus and the hazards involved. The clearance requirements of the NESC inside a substation are not as stringent as the clearance requirements for electrical facilities located in areas accessible to the general public because the substation is not accessible to the general public. When we allow the general public (non-qualified persons) in substations, we are asking for trouble.
How do we keep non-qualified people out?
1. The surrounding fence must be at least 7-foot tall (Rule 110A1). Because chain link fences are so easy to climb, particularly by children, it is my opinion that a chain link fence without barbed wire is not an effective barrier. When the grade is raised next to a fence, the fence height must be adjusted. (See photo 1)
Remove Aids to Climbing:
If a parking lot is adjacent to a substation, appropriate barriers should be used to prevent vehicle parking and dumpsters up against the fence.
2. The fence and gates must extend to the ground. The roadway under gates must be reconditioned after heavy use. If the roadway under gates is subject to washout, the roadway should be paved. (See photo 2:)
3. Warn the public of the hazards inside the substation with appropriate WARNING signs in compliance with ANSI® standard Z535 at least at each entrance and on each side (Rule 110A1). ANSI Z535 recommends that the signs shall be so placed to alert the viewer in sufficient time to take appropriate action to avoid harm.
4. Do not store materials within a substation even if such materials are stored well away from energized conductors and equipment (Rule 110B2). The storage of materials within a substation invites non-qualified personnel like material delivery personnel and thieves.
The second most common substation hazard is lack of grounding. (See photo 3)
The metal fence surrounding the substation and all non-current-carrying metals parts within the substation must be electrically bonded together and effectively grounded (Rule 123A). The grounding methods must be in compliance with Section 9 of the NESC. The grounding must be designed to limit tough, step and transferred voltages in accordance with industry practice. IEEE standard 80 is one source that may be utilized to provide guidance in meeting these requirements. To meet these requirements, usually a ground grid must be installed under the substation with grounding conductors bonding the fence and non-current-carrying parts to the grid.
The most common hazard I see with overhead lines is inadequate ground clearance or clearance to other structures, particularly signs.
Most overhead hazards are created by people who change the environment around the supply facilities, not by the people who originally constructed the facilities. For example, an overhead high voltage line was constructed to serve a large industrial company. The property between the utility service point and the customer’s substation was designated “employee parking.” The line was designed to meet the vertical clearance requirements of the NESC as stated in Rule 232 for an area accessible to truck traffic. Five years later, the management of the company decided to make the employee parking lot into a raw material storage area complete with a crane to move the materials. The use of the land under the overhead line was changed. The line should have been moved. (See Photo 4 & 5)
If you have general questions about the NESC, please call me at 302-454-4910 or e-mail me at firstname.lastname@example.org.
National Electrical Safety Code, NESC and IEEE are registered trademarks of the Institute of Electrical and Electronics Engineers. ANSI® is a registered trademark of the American National Standards Institute. ANSI Z535 is a publication of the National Electrical Manufacturers Association (NEMA).