From the documentation:
General grounding requirements
Two safety grounds are required to ensure safe operation of the G450 Media Gateway: the ground conductor that is part of the AC power cord and the field-installed green/yellow conductor referred to as the Supplementary Ground Conductor. Both safety grounds must be
connected to an approved ground. If a power cord accompanies the G450, use that cord whenever possible.
Installation location The customer must select a location for the G450 Media Gateway installation that is no more than 25 ft (7.6 m) from an approved ground. If this location requirement is not met, the customer
must contact a licensed electrician to install a Supplementary Ground Conductor per Article 250 of the National Electrical Code (NEC).
Partnumber 700236680 1 Grounding Kit for multiple G450s in a 19 inch rack