Lack of grounding as per the Hardware guide, you may run the risk of encountering one or more of the following issues:
If the AC powered EX Series switches are already installed in your facility without the ground lug connected, the 2-hole protective earthing terminal of Juniper EX- series switches can still be connected to the facility’s earth ground with the EX-Series switches running.
NEBS-compliant system installed in NEBS environments, and DC powered systems must be connected to ground though the 2-hole protective lug (earthing terminal).
All Juniper systems have been tested for EMI/EMC compliance using the 2-hole protective earthing terminal to connect the system to ground. To prevent non-compliance and potential EMI/EMC issues, it is essential to use the 2-hole protective earthing terminal to connect the system to ground, in addition to the power cord ground. The best grounding practices should be followed as far as possible. Electromagnetic noise problems are not anticipated, but installing a best-practice grounding system is always recommended.