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Short Circuit Withstand Tests - UL vs IEC

FROM: Ferraz Shawmut SAS - 15, rue Jacques de Vaucanson - F69720 SAINT BONNET DE MURE
CONTACT: Hervé Le Penven - Communications Manager
AGENCY: Infocom Industrie - Amel Karim +33 472336598

Are we testing the same thing?

Short circuit tests on the same model of our Surge Trap® surge suppressor devices give significantly different results when the product is tested as per IEC standard 61643-1 than when UL 1449, 3rd edition, is followed.
For instance, our STP230TN1M model for AC application has 25 kA short circuit current withstand according to IEC 61643-1 whereas its short circuit current rating is 200 kA under the UL 1449 standard!

This is easily explained once you realize the two standards are seeking quite different things.
IEC 61643-1's test (§ 7.7.3. Short circuit withstand) checks the withstand of the SPD's casing, and not that of its active element. In fact, it is clearly specified that the active element is replaced with a copper block during the test. But in UL's Short Circuit Current Rating (SCCR) test, the SPD is tested as a unit. The purpose here is to check whether the product is capable of protecting itself, either internally or via an external disconnector, from high short circuit currents.

As far as our Surge Trap® is concerned, the TPMOV® internal active part has an SCCR of 200 kA under UL 1449. As soon as the current rises, the internal disconnecting shield moves to isolate the metal-oxide varistor from the test circuit.

That is why the stated values in our Helio Protection Program and Surge Trap® literature are so widely different.