Understanding Joule Ratings in Surge Protective Devices (SPDs)

Issue

Clarification on the relevance and accuracy of Joule ratings in evaluating SPD performance.

Applies To

• Product Lines: EMA SPD, EBA SPD, HWA, TVSS, Surgelogic
• Environment: All installations and applications utilizing the above SPD models

Resolution

Joule ratings are not a recognized or reliable metric for determining the effectiveness or performance of a Surge Protective Device (SPD). While often referenced in marketing materials, the Joule rating does not provide an accurate representation of an SPD’s protective capabilities.

In the surge protection industry, the Peak Surge Current Rating—also known as the kA Rating or Maximum Current Rating—is the industry-accepted standard for evaluating SPD performance. This rating indicates the maximum surge current the internal Metal Oxide Varistor (MOV) can safely withstand without sustaining irreversible damage.

For accurate performance assessment and product comparison, always refer to the SPD’s kA rating as defined by UL 1449 and the manufacturer’s specifications.

Additional Notes

• The kA rating reflects the robustness and durability of the SPD under high-energy surge conditions.
• Relying on Joule ratings can lead to misinterpretation of a device’s actual protective performance.

Released for: Schneider Electric Canada