UL 1449 is the North American safety standard for surge protective devices, and it plays a role in the United States and Canada that is different from that of the corresponding international standard: rather than defining a performance characteristic for a designer to select against, it is a safety standard applied by a certification body, and a device that does not carry the mark cannot normally be installed in a listed assembly. Its best known contribution is the voltage protection rating, a value established under a specified test current that appears on the label and allows devices to be compared directly, and it also defines the tests that establish that a device will fail safely, which means that a device which reaches the end of its life must not overheat, rupture or create a shock hazard. The standard covers cord connected, permanently connected and receptacle type devices and draws a distinction between them in the requirements it applies.