NEBS certification is not a single "pass/fail" test, but a series of evaluations based on GR-63-CORE and other standards like GR-1089-CORE.
Because GR-63-CORE is a proprietary, copyrighted technical standard managed by Ericsson (formerly Telcordia Technologies), gr63core issue 5 pdf link
GR-63-CORE is a copyrighted document and is not legally available for free download. To obtain the official PDF, you must purchase it from authorized standards distributors. The document is available for purchase from several official sources: NEBS certification is not a single "pass/fail" test,
The main objective is to protect equipment and ensure reliable network operation under extreme and demanding conditions. forming a comprehensive NEBS compliance suite.
GR-63-CORE works with a companion standard, GR-1089-CORE, forming a comprehensive NEBS compliance suite.