Surge Protection Devices - Zone Approach and Uniformity

Dangerous surges often enter a structure through the electrical utility.  These surges can be from lightning strikes on the line, malfunction of equipment, or the normal switching and operation of transformers.  Often, these surges go undetected because they do no initial damage to equipment, but they can weaken equipment and lead to a premature failure or make failure more likely when a larger surge does take place.  The best method to prevent against such damage is through the use of electrical surge protection devices (SPDs) at the service entrance, sub-panels and point of use.  This is known as a zone approach because it protects each zone or step in the electrical distribution process.  At present, the 911 center only uses SPDs at the point of use of selected equipment.  Related to this, we recommend your organization evaluate having an SPD installed on the main electric panel and sub-panel, and that you provide point of use SPDs for all critical equipment, such as that located in the radio and phone rooms.  The selection and installation of a main or sub-panel SPD should be done by a qualified contractor.  Your organization may also want to use this contractor to provide a recommendation on the point of use SPDs, but we noted these should at least meet UL 1449 3rd edition to assure a satisfactory level of safety.  SPDs should also have a positive indicator that they are functioning properly, and many of the models used for main panel protection can provide power quality information or have power conditioning capability.  As previously noted, the effectiveness of most surge protection devices relies on a quality, low impedance path to ground.