~ National Lightning Safety Institute ~
Guidelines For Providing Surge Protection at Commercial, Institutional, and Industrial Facilities
By Matthew T. Glennon, P.E.
Damage from electrical transients, or surges, is one of the leading causes of electrical equipment failure. An electrical transient is a short duration, high-energy impulse that is imparted on the normal electrical power system whenever there is a sudden change in the electrical circuit. They can originate from a variety of sources, both internal and external to a facility.
Not Just Lightning
The most obvious source is from lightning, but surges can also come from normal utility switching operations, or unintentional grounding of electrical conductors (such as when an overhead power line falls to the ground). Surges may even come from within a building or facility from such things as fax machines, copiers, air conditioners, elevators, motors/pumps, or arc welders, to name a few. In each case, the normal electric circuit is suddenly exposed to a large dose of energy that can adversely affect the equipment being supplied power.
The following are surge protection guidelines on how to protect electrical equipment from the devastating effects of high-energy surges. Surge protection that is properly sized and installed is highly successful in preventing equipment damage, especially for sensitive electronic equipment found in most equipment today.
Grounding Is Fundamental
A surge protection device (SPD), also known as a transient voltage surge suppressor (TVSS), is designed to divert high-current surges to ground and bypass your equipment, thereby limiting the voltage that is impressed on the equipment. For this reason, it is critical that your facility have a good, low-resistance grounding system, with a single ground reference point to which the grounds of all building systems are connected. Without a proper grounding system, there is no way to protect against surges. Consult with a licensed electrician to ensure that your electrical distribution system is grounded in accordance with the National Electric Code (NFPA 70).
Zones Of Protection
The best means of protecting your electrical equipment from high-energy electrical surges is to install SPDs strategically throughout your facility. Considering that surges can originate from both internal and external sources, SPDs should be installed to provide maximum protection regardless of the source location. For this reason, a "Zone of Protection" approach is generally employed. The first level of defense is achieved by installing an SPD on the main service entrance equipment (i.e., where the utility power comes into the facility). This will provide protection against high energy surges coming in from the outside, such as lightning or utility transients.
However, the SPD installed at the service entrance will not protect against internally generated surges. In addition, not all of the energy from outside surges is dissipated to ground by the service entrance device. For this reason, SPDs should be installed on all distribution panels within a facility that supply power to critical equipment. Similarly, a third zone of protection would be achieved by installing SPDs locally for each piece of equipment being protected, such as computers or computer controlled devices. Each zone of protection adds to the overall protection of the facility as each helps to further reduce the voltage exposed to the protected equipment.
Coordination of SPDs
The service entrance SPD provides the first line of defense against electrical transients for a facility by diverting high-energy, outside surges to ground. It also lowers the energy level of the surge entering the facility to a level that can be handled by downstream devices closer to the load. Therefore, proper coordination of SPDs is required to avoid damaging SPDs installed on distribution panels or locally at vulnerable equipment. If coordination is not achieved, excess energy from propagating surges can cause damage to Zone 2 and Zone 3 SPDs and destroy the equipment that you are trying to protect.
When selecting an SPD for a given application, there are several considerations that must be made:
Data Line Protection
Electrical transients are not confined to the electrical distribution system. They can enter a facility through phone/fax lines, cable or satellite systems, and local area networks (LAN). Therefore, in order to achieve maximum protection from surge damage, SPDs should be installed on all systems susceptible to electrical transients.
For maximum protection, SPDs should be installed as close to the equipment being protected as possible. Cable lengths should be as short and straight as possible to minimize the resistive path of the circuit to ground. A solid connection to the system grounding conductor is essential for proper operation of the SPDs. The surge protectors should be equipped with indicators that show if the circuit is grounded and operating properly, and the units installed so these indicators can be easily inspected.
All service entrance and distribution panel SPDs should only be installed by a licensed electrician familiar with the equipment and its use. In addition, Hartford Steam Boiler strongly recommends that a professional engineer experienced with surge suppression technology be retained to design the protection scheme for your facility to ensure all SPDs are properly sized and coordinated.
Depending on the application and ratings, SPDs for service entrance equipment range from $150-$6,500. Data line and AC receptacle protection ranges from $20 - $150.
Matthew Glennon works for the Hartford Steam Boiler Inspection and Insurance Company as the AVP of Electrical Loss Control. A registered Professional Engineer in New Jersey with over 14 years of experience in electric power engineering and construction, Mr. Glennon is a magna cum laude graduate of Manhattan College in New York where he earned a Bachelor of Engineering degree in electrical engineering. In addition, he holds a Master of Engineering degree in electric power engineering from Rensselaer Polytechnic Institute (RPI) in Troy, N.Y., and an MBA in Finance from Rutgers University in New Jersey. He is certified by the AEE as a Power Quality Professional and by the NLSI as a Lightning Safety Professional. Mr. Glennon is member of IEEE, NFPA, and the National Society of Professional Engineers (NSPE), as well as a Correspondent to the National Academy of Forensic Engineers (NAFE) and an affiliate to the InterNational Electrical Testing Association (NETA).