Few events can match the destruction caused by surges and electrical noise. These phenomena are responsible for about 50 percent of most electronic equipment failures today.
Since microprocessor-based equipment functions with faster operating speeds and lower operating voltage than other equipment, surges and electrical noise previously classified as non-threatening are significantly more damaging. An electrical surge 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. It can originate from a variety of sources, both internal and external. The most obvious external 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 can also enter the premises via internet cable and telecommunications lines. However, numerous studies have shown that exterior sources account for only 20% of all electrical surges. The remaining 80% can be accounted for by equipment within a facility. Known sources of surges and noise within a building or facility include everyday items such as fax machines, copiers, air conditioners, elevators, and motors/pumps. In each case, the normal electric circuit is suddenly exposed to a high voltage signal that can adversely affect the equipment being supplied with power.
Surge Protection Device
A surge protection device (SPD) is designed to absorb and divert high-voltage surges to ground and bypass connected equipment. This action limits the voltage that is impressed on the equipment. The most common component of every SPD is the metal oxide varistor (or MOV). The MOV acts as a very high-speed switch and diverts the energy to ground. An important concept about the SPD is that it is a sacrificial device with degradation of performance over time. It is considered to be at the end of its life when it has lost 10% of its design capacity.
A very important feature is a diagnostic indicator (light or alarm) to verify that it is still functioning and hasn’t been disabled from the last surge suppression event.
Only surge protection that is properly sized and grounded can be successful in preventing equipment damage. For maximum protection, SPDs should be installed as close to the protected equipment as possible, and cable lengths should be as short and straight as possible to minimize the resistive path of the circuit to ground. Three key points must be addressed regarding grounding and bonding.
A licensed electrician should complete these three steps:
- Evaluate the facility’s grounding for NEC compliance. All outlets should be checked for proper polarity and properly connected equipment grounding conductors.
- Determine if the grounding system is robust enough to fulfill the function of the SPD by checking for proper wire size and tightness of connections.
- Determine specific corrective action required to bring the grounding network to both NEC compliance and to the level of performance to address surges and electrical noise.
Zone of Protection
One of the primary recommendations set forth in IEEE 1100 is the implementation of “Zones of Protection.” Considering that surges can originate from both internal and external sources, SPDs should be installed to provide maximum protection regardless of the source location.
The three zones include:
- The first zone is at the service entrance where the most robust SPD is placed to divert surges coming from external sources such as lightning. Type-1, SPD devices.
- The second zone of protection is within the facility at locations identified as susceptible to surges. Type-2, SPD devices and are installed on equipment such as switchboards, panel boards, motor-control centers.
- The third zone of protection is at the outlet, or point of use. Type-3, SPD devices.
It is strongly recommended that a professional engineer experienced with surge suppression technology be retained to design the protection system to ensure all SPDs are properly sized and coordinated.
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. The service entrance SPD provides the first line of defense against electrical surges for a facility by diverting high-energy, outside surges to ground. It also lowers the energy level of the surge entering the facility that can be handled by downstream devices closer to the load. Proper coordination of SPDs avoids damaging SPDs installed on distribution panels or other vulnerable equipment. If coordination is not achieved, excess energy from propagating surges can cause damage to Type-2 and Type-3 SPDs and destroy the equipment you are trying to protect.
Depending on the application and ratings, SPDs for service entrance equipment range from $500 – $6,500. Data line and AC receptacle protection ranges from $25 – $150.
Although surges and electrical noise cannot be totally eliminated, they can be mitigated through an engineered approach to reduce their damaging effects. This leads to greater reliability and overall improved productivity. In this regard, surge protection is an inexpensive form of electrical system insurance.