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Can Your SPD Go to Extremes?

Jul 1, 2008 12:00 PM, By Carey Mossop and Alan Chiste, Eaton Corp.

SPD Testing

Surge protective device (SPD) manufacturers must adhere to numerous tests, which should undergo independent verification. UL 1449 is the most commonly applied standard for SPDs in North America. Tests in UL 1449 are designed to address the most common failure modes of SPDs: sustained TOVs. This is accomplished by two major sets of tests, the abnormal overvoltage limited current tests and the abnormal overvoltage unlimited current test. To pass the tests, the device must not produce a fire or shock hazard during or after the tests.

The abnormal overvoltage limited current test is conducted by applying an abnormal overvoltage (e.g., up to twice the rated voltage) to the SPD via a conductor pair, which is connected to two of the following SPD terminals: phase-to-neutral, phase-to ground, and neutral-to-ground. Prior to February 2005, the requirement of the test was to limit the current to 0.125A, 0.5A, 2.5A, and 5A by means of the power-source impedance. In February of 2005, UL 1449 was expanded to include abnormal overvoltages with currents limited to 10A, 100A, 500A, and 1,000A. Compliance to these tests was required by February 2007. This had a major impact on the SPD market as a number of SPD manufacturers stopped making SPDs completely, dropped models of SPDs that could not pass the tests, or redesigned their SPDs.

The abnormal overvoltage unlimited current test is conducted in the same manner, except the impedance must allow for a current of at least 5,000A. The manufacturer chooses what level of available current it wants to subject the SPD to. This value is called the short-circuit current rating (SCCR). The end-user must note the difference when comparing the SPD SCCR with the interrupting or withstand ratings of other system components, such as circuit breakers, contactors, and relays. The SPD SCCR is tested at abnormal overvoltage, and other components are usually tested at nominal system voltage. For example, on a 120/208V SPD, the test will apply a line-to-line voltage (208VAC) on a phase-to-neutral SPD terminal (120VAC). These are important tests because they relate directly to equipment and personnel safety.

Mossop is product line manager for Surge Protection and Power Factor Correction for Eaton's electrical business in Pittsburgh. He can be reached at CareyBMossop@eaton.com. Chiste is product sales manager for power quality products for Eaton's electrical business in Seattle. He can be reached at AlanRChiste@eaton.com.

Editor's Note: The original version of this article was previously published in Power Quality magazine in 2001 and is updated to reflect recent changes included in UL 1449, 3^rd edition.

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