GR-63-CORE is a standard developed by Telcordia (now part of Ericsson) that focuses on the protection circuits used in network and element level equipment. It provides detailed requirements for the design, testing, and qualification of protection circuits to ensure reliable operation in various environmental conditions.
GR-63-CORE Issue 5 (December 2017) defines essential NEBS™ standards for telecommunications equipment, covering physical, environmental, and seismic criteria . This update by Telcordia Technologies (Ericsson) gr63core issue 5 pdf link
Are you also looking for the companion electrical standard, ? GR-63-CORE is a standard developed by Telcordia (now