All ac power SPDs should be UL 1449 Listed or Recognized and installed on the load side of the main disconnecting device. Non – UL approved devices may create a fire or personal safety hazard.
Most commercial SPDs are hard wired to the facility electrical system. The primary primary function of the SPD is to eliminate short duration voltage spikes by diverting the excess voltage to ground.
A requirement for a good performing SPD is to install the device with a low resistance path to ground. Without a low resistance path to ground the surge may go through an undesirable path inside expensive electronic equipment. The surge may also cause the SPD to overheat and fail prematurely. SPDs should be installed in accordance with the manufacturers installation instructions. These installation instructions should detail what size conductors to use and if the unit must be installed with an over-current device such as a fuse or breaker. If the installation instructions are not followed a hazardous condition may be created.
* ANSI/UL 1449-2006 (Third Edition) replaces UL 1449 Second Edition. With regard to performance ratings associated with these standards, there are some important differences to be understood. The changes are outlined below.
UL 1449 Second Edition
- SPDs are marked with a Suppressed Voltage Rating (SVR) that is obtained using a 6 kV, 500 A Combination Wave Generator.
- SPDs are limited to application on the load side of the main service equipment unless complimentary listed as a surge arrester.
UL 1449 Third Edition
- SPDs are marked with a Voltage Protection Rating (VPR) that is obtained during the Nominal Discharge Current test using a 6 kV,3 kA Combination Wave Generator. The VPR marking replaces the SVR marking. It should be noted that the VPR is obtained using a much larger short-circuit surge current.
- SPDs are marked with a Nominal Discharge Current Rating that is verified to ensure that the SPD is fully operational when subjected to 15 surges at the marked level. Nominal Discharge Current Ratings include 20 kA, 10 kA, 5 kA and 3 kA.
- SPDs are marked with an SPD “Type” that indicates where the SPD can be installed within the electrical system.
Conditions of Acceptability
One important aspect of SPDs that is often misunderstood is the difference between a “listed” SPD and a “recognized component”. A listed SPD is one that has met all of the requirements of the UL 1449 standard (regardless of the edition). A recognized component SPD is one that may not have been subjected to all the requirements of the UL 1449 standard and is assigned “conditions of acceptability”. Contact the SPD manufacturer to determine the conditions of acceptability.