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Table 3 of ANSI/ESD S20.20-2007 has the required limit for Mobile Equipment (working surfaces), such as on carts, to be RTG (resistance to ground) less than 1 x 10E9 ohms. So cart should be grounded while being moved via a drag chain or conductive casters to an ESD Floor.
Compliance Verification ESD TR53 for carts should be measured for RTG using one 5# electrode. The objective of this periodic test procedure is to verify the resistance of the Cart grounding system (cart through grounded floor). A well-designed Cart compliance verification program not only tests the Cart, but also indicates the quality of the conductive path through the cart and floor grounding system.
Regarding your conveyor / flow rack system, the roller / rack system should be grounded. Per ANSI/ESD S20.20-1999 section 126.96.36.199. Automated Handlers “All conductive or static dissipative components of automated handling equipment should provide a continuous conductive path to ground, whether stationary or in motion. The equipment should minimize charge generation of the ESDS [ESD sensitive] items that are handled. Where insulative materials are necessary in the device path, they should be designed to minimize electric fields and the charge imparted to devices being handled.”