To clarify a little:
The system to be implemented is a set of PoE cameras feeding video to an outdoor telecom cabinet which will have the PoE and data equipment necessary to power the cameras on and transmit video feed to a remote site.
As per TIA-607, I understand I should supply grounding for the telecom equipment separately from that of the mains line, however this isn't mandatory.
One of the options is to insert a ground rod to ground the cabinet and the chassis of the equipment to be installed, however, IEEE Std 142-2007 specifies 5 ohms ground impedance for sensitive equipment. Since I can't just drill the current foundation to just test the soil BEFORE placing a bid, I want to know if it's safe to assume the soil behind a foundation would be wet and with low impedance (the soil seems to be clay), or if the safest route is to assume I will need to make room to put grounding back fill.
The other option is to ground the cabinet and the chassis of the equipment using the grounding wire of the mains line. However, I don't know if there's any other restrictions (my knowledge of the IEEE recommended grounding practices is, to be honest, far from perfect).