There is no ground wire connecting the outlets on single phase Symmetra backplate PDUs, i.e. SYAPD1, SYPD3, etc, to earth ground.
All serial ranges
These PDUs ground themselves (and the equipment that a customer attaches to them) without the use of a ground wire running between the receptacles and the PDU housing or UPS chassis.
This is not a problem. The PDUs are grounded using another reliable method.
The UPS chassis is connected to earth ground by the installing electrician when the UPS is being installed and started up. This grounds the UPS chassis. Now that the chassis is grounded, anything directly connected is also grounded. This includes any backplate PDUs connected to the system since there is direct metal-to-metal contact between the PDU and the UPS chassis. The individual receptacles on the PDUs themselves are grounded by their metal to metal contact with the metal PDU housing when they are installed and screwed down. As a result, the PDU, all of its receptacles, and anything plugged into the receptacles are connected to the same earth ground provided to the UPS by the installing electrician.