More than One Criteria
By Ken Lovorn, P.E., Lovorn Engineering Associates, LLC, Pittsburgh -- Consulting-Specifying Engineer, 11/1/2004
Surge suppressors are rated by their single-pulse, maximum surge current per mode. However, a number of other criteria should be considered, such as how they respond to the various ANSI/IEEE waves and the relative let-through current resulting from each of the waves—i.e., B3, B3/C1 combination wave and C3. A single surge suppressor on the service entrance of a facility won't provide adequate protection for sensitive electronic drives, microprocessor-based systems, personal computers and other solid-state, electronic equipment in today's corporate and institutional facilities. As a minimum, a service-entrance-rated surge suppressor should be installed on the main switchboard; a panelboard-rated surge suppressor should be installed on the branch circuit panel feeding the sensitive equipment; and an equipment-rated surge suppressor should be installed at the utilization equipment.
The one element of installation that is most critical for the performance of the system is the routing and length of the conductors connecting the TVSS to the distribution system. In fact, conductor length should be kept to an absolute minimum, and conductor runs should include few bends, preferably none. Necessary bends should be sweeping, not 90 degrees. Finally, keep the conductor properly sized for the equipment. These steps should keep conductor impedance to a minimum and reduce the clamping voltage to its minimum value.
As part of the installation procedure, the installer should test the unit to confirm that surges are clamped to published levels and that the unit has acceptable surge handling capabilities. These two tests should also be run periodically as part of maintenance to confirm proper system operation.
TVSS Systems| Light Duty | Medium Duty | Heavy Duty | Severe Duty | |
| Max. Surge Current | 60,000 to 125,000 amps | 80,000 to 160,000 amps | 150,000 to 200,000 amps | 300,000 to 450,000 amps |
| Application | Residential and light commercial services. | Small commercial services. Branch circuit panels. Less frequency of lightning. | Smaller service entrances. Critical branch circuit panels. Distribution panels. Lightning-intense areas. | Service entrances, 2,000 to 4,000 amps. Lightning-intense areas. |
| Relative Cost* | 1 | 2.2 | 4.4 | 6.2 |
| Desirable Characteristics | High repetitive surge capacity—i.e., ability to handle a high number of C3 waves. Module and protective fuse replacement by the user. Lowest clamping voltage for each of the test waves. | |||
| Common Characteristics | Multiple mode operation: Line-Line, Line-Ground, Line-Neutral, Neutral-Ground. Replaceable modules. Extended Warranty, up to 10 years. Meet UL 1449. | |||
| Optional Equipment (not available on all units) | Remote alarm and monitoring. Surge counter. Internal disconnect. Fused disconnect. Retrofit onto existing panel. Installation within a new panel or switchboard. EMI/RFI noise filter. Diagnostic monitoring. | |||
| *Costs are relative and based on comparable equipment and options. The figure starts with the simplest device as a cost of "1" with the others being a multiple of that cost. | ||||
